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Table of Contents
Does a radio need an antenna?
Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. Radio waves are electromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss.
Can I hook up my car stereo directly to battery?
Yes, you can connect a car stereo directly to a battery. However, you will have to make sure that the battery that you are connecting it to is a 12-volt battery. Preferably, it should also be a car battery.
Can I take the antenna off my car?
Luckily, you can remove and repair the antenna yourself for under $20 and a quick trip to the auto parts store. The most common type of antenna is pillar-mounted, which slides easily in and out of the holder. You can unscrew and pull out the old unit.
How to Wire a Car Stereo to a 12v Battery
The most common type of antenna is a column antenna that slides easily in and out of the mount. You can unscrew and pull out the old unit. Replacement antennas are easy to find at an auto parts store or online retailers like Amazon. Once you have a new antenna, plug the wires for the new antenna into the existing wires in the mount.
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MORE: 9 Best Road Trip Destinations for Music Lovers in the US
What happens when your car antenna breaks?
As car antenna protrudes and stands on the surface of a car’s exterior, it tends to break or suffer damage often and easily. … Your radio may be turned off if you don’t have an antenna. You will have trouble with your reception with a damaged radio antenna.
How to Wire a Car Stereo to a 12v Battery
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What can I use for an FM antenna?
A dipole antenna is often an ideal solution for an antenna for receiving VHF FM broadcasts.
How to Wire a Car Stereo to a 12v Battery
Dipole antennas include:
Dipole Antenna Basics Current & Voltage Half Wave Dipole Folded Dipole Short Dipole Doublet Dipole Length Dipole Feeds Radiation Patterns Construction RF Ham Dipole Inverted V Dipole RF Multiband Fan Dipole RF Multiband Trap Dipole G5RV Antenna FM dipole design
One area where dipole antennas are commonly used is in receiving VHF VHF radio broadcasts. Many hi-fi tuners and other radios have input jacks that accept input from a coaxial feed and where an external antenna is not used a dipole antenna can be an excellent solution.
The FM dipole antenna will most likely offer greatly improved reception over many other improvised solutions that can be used.
It’s pretty easy to make a simple DIY FM dipole antenna. They can be made in a variety of ways and at minimal cost. They can prove to be an ideal solution for an internal VHF antenna, possibly in the attic or roof space, or they can be used where a temporary antenna is needed.
If they are to be used indoors, there is no need to use expensive materials to protect them from the elements. Instead, the DIY VHF FM dipole for internal use can be made from commonly available materials, and so the cost is likely to be minimal. It may even be possible to build a simple FM dipole from items that may already be in a dustbin or in a workshop or garage.
Basics of the dipole antenna
The dipole antenna consists of two poles or parts. In a half-wave dipole, each leg of the dipole is one quarter electrical wavelength long.
The length of the dipole is determined by the operating frequency. The FM broadcast band extends from 87.5 MHz to 108 MHz. This is quite a wide range that can be covered by a resonant antenna like the dipole antenna, but since it’s only used for receive, the power at the band edges isn’t as important as it would be if it were used for transmit.
The basic design for the VHF dipole antenna is shown below.
Simple half-wave dipole antenna
In the figure, each leg of the dipole antenna is connected to the feeder. This can either be open wire/dual feed or coax can be used. Strictly speaking, when using coax or coaxial cable, a balun should be used. Because coax is a so-called unbalanced feeder, i.e. the outer shield is grounded and the antenna is balanced. However, for this application no noticeable degradation should be seen and the VHF FM dipole antenna should perform fairly satisfactorily without one. In this case the inner conductor of the coaxial cable is connected to one leg of the dipole and the outer conductor (braid) of the coaxial cable is connected to the other leg of the dipole antenna.
How to make the simple do-it-yourself FM dipole antenna design
Few parts are needed to make the simple DIY VHF dipole antenna. Typically these are:
Twin-Flex – Twin power cord is an idea, but we used old speaker wire.
Cable ties – to secure the center of the dipole and prevent the flex from opening beyond what is needed.
String or twine to attach the ends of the dipole to the appropriate attachment points (if needed).
Male – if it is to be connected to a coaxial cable.
Components required to make a VHF dipole antenna
One benefit of using power flex cable is that when used as a feed for high frequency signals, this type of cable is a fairly close approximation of a 75 ohm twin or open wire feed. This comes in handy when a reasonable length is needed. We used cheap speaker wire to make our FM dipole antenna.
Twinflex FM dipole
To make the VHF FM dipole antenna, the two insulated wires of the cable should be separated and opened first. The center should then be secured to prevent the cable from opening further. One method of doing this is to use a zip tie, which is available from most electronic component retailers. The length of wire that has not been split can then be used as a feed line for the antenna.
A cable tie can be used to secure the center point of the VHF dipole antenna
The total length of the antenna should be about 150 cm, i.e. each leg should be 75 cm long. This length should cause the resonant frequency to fall slightly in the lower half of the FM broadcast band, but often the more popular stations are found in this region. If the resonant frequency is to be higher, the antenna can be shortened slightly.
It’s fairly easy to calculate length from one of the following equations:
Length (meters) = 150 A f
Length (inches) = 5905 A f
Sometimes the equations will vary a bit in the constants used, as this depends on a variety of factors including the cable used, the environment, the frequency, and the like. However, it’s a very good starting point and certainly good enough to make the VHF dipole antenna.
The ends of the wire can be knotted as shown so it can be attached to string or twine for display in an attic etc. When this is done, the length should be taken to the end of the wire and, if necessary, wire that is part of the knot or double back should not be included in the length. Knotting the cord adds some inductance to the end of the cord, which might make it a bit long, but it should be fine for reception.
The wire end of the FM dipole is knotted
As we already had some coax installed around the house, our antenna was connected to a coax connector and a matching version attached to the coax. It should be noted that twin feeders, like the one formed by the flex, do not perform well when passed through a house for long distances, and signal losses increase – it is better to use coax, as this does not affect the same way is affected.
When installing the antenna as far as possible on a roof, the antenna should be away from metal objects as this will reduce signal levels. The ends of the antenna in particular are more sensitive to nearby metal objects.
We hung our antenna in the attic or attic. Since many FM VHF stations use vertical polarization these days, we mounted the dipole vertically: one end attached to a handy nail in the wooden constriction of the roof, and the other end held down by a weight. The coax was led away at right angles – as far as it is possible under these circumstances!
How to make a VHF FM folded dipole antenna?
Many VHF FM HiFi tuners have a 300 ohm input in addition to the standard 75 ohm input. This input usually has screw terminals, although sometimes they have a dedicated 300 ohm connector. This input is ideal for use with a VHF FM folded dipole antenna which is very easy to set up. It only requires the use of a 300 ohm ribbon cable (not the multi-wire computer ribbon cable) available at most electronic component retailers.
The first stage is to cut a slightly longer length than required for the dipole element. At both ends, the middle plastic should be cut back and the remaining wire stripped and joined on both sides. It is important to ensure that the total length of the element is correct.
The next step is to cut the bottom wire down the middle. The wires should be stripped to allow a second length of tape to be attached. This can be of any suitable length, bearing in mind that it is likely to result in a reasonable loss if operated close to other objects indoors. This allows the 300 color ribbon to be connected as a feeder. This can be any suitable length.
This inexpensive and simple FM VHF dipole antenna is suitable for areas with high signal strengths or can be used as a temporary measure. The 300 ribbon cable is generally transparent and can be hidden quite well. Often this type of antenna can be mounted behind a curtain rod or a large piece of furniture.
A dipole antenna is often an ideal solution for an antenna for receiving VHF FM broadcasts. The VHF dipole antenna can be a cheap and effective solution, and it can be made in a variety of forms – only two ideas were given above, but it is possible to make a VHF VHF dipole antenna in many more ways depending on the needs at hand are and what the requirements are.
Other antenna and propagation topics:
EM waves Radio propagation Ionospheric propagation Surface wave Meteorite scattering Tropospheric propagation Cubic Quad Dipole Discone Ferrite Rod Logarithmic Periodic Antenna Parabolic Mirror Antenna Phased Array Antennas Vertical Antennas Yagi Antenna Grounding TV Antennas Coaxial Cable Waveguides VSWR Antenna Baluns MIMO
Return to the Antennas & Propagation menu. . .
How do you make a homemade FM antenna?
- Cut a length of speaker wire.
- Split the two wires into single length pieces.
- Strip insulation from one end of each length of single cable exposing about one inch.
- Strip about one inch of insulation from the end of the antennae leads.
- Twist the exposed wire of one extension to one antennae lead.
How to Wire a Car Stereo to a 12v Battery
Techwalla may receive compensation through affiliate links in this story.
Does FM radio need an antenna?
Statement from Radio Bob: You MUST have an antenna (of some kind) to receive any signals on a radio! Another statement from Radio Bob: FM Radio Waves travel more-or-less in straight lines. They are weakened by objects that get between the transmitter and receiver.
How to Wire a Car Stereo to a 12v Battery
A good radio A good antenna A good location
If you have all three, you can potentially pick up an FM station up to 100 miles away! However, most of us only have one of these items at best
RADIOS: For good reception, a radio must have good selectivity (selectivity is a radio’s ability to separate weak, nearby, on the FM dial, strong stations) and good sensitivity (the ability to pick out weak, distant stations at all). to recieve!)
Car radios: You probably already have a radio with these functions. This radio is in your car. Car radios must be built to high standards to ensure decent reception in a moving vehicle over variable terrain and with a serious source of interference nearby (your engine!). Surely you’ve noticed that FM radio reception in your car is usually better than at home. This is partly because your car radio is probably better than your home radio.
Home/Office Radios: Most home radios have poor selectivity and sensitivity (we like to call them “junk” in the radio business). Typical $19.95 radios with analog tuning (as opposed to digital tuning, which shows the radio station’s frequency in illuminated numbers) will work, but only near a radio station’s transmitter. Most clock radios, under cupboard radios, “boom boxes”, crank radios, etc. just don’t work very well, especially when compared to a car stereo!
Boston Acoustics Horizon Solo
Boston Acoustics Horizon Duo
Tivoli Model One
Sangean WR-2
SONY XDR-F1HD
RadioBob recommends:
Ripping a car stereo out of a car, building a 12 volt DC power supply, building a really cool Honduran mahogany or purpleheart case, and finding some nice external speakers.
OK, seriously, there are some great radios out there, yes they cost more than a $19.95 disposable plastic radio, but they are MUCH better. They sound great and are a quality product. Today (early 2009) I would recommend the Boston Acoustics Horizon Solo clock/table radio for around $100. Or the stereo version (the Boston Acoustics Horizon Duo) for $150. Then there’s the Tivoli “Model One” if you don’t need a watch, and like a “retro” analog tuning wheel (around $140) or even the button-filled Sangean WR-2 (also around $140).
If you happen to have a component stereo system (typically separate amplifier/tuner with separate speakers), your tuner may already have decent sensitivity and selectivity. Try connecting a better antenna (see below) and see how your reception improves! If you’re looking to buy a state-of-the-art FM tuner (at a very reasonable price), get the SONY XDR-F1HD (under $100). Reviews have ranked this as one of the best tuners ever built! Remember that you must have an external amplifier and speakers for this!
ANTENNA/LOCATION LOCATION/ANTENNA ANTENNA/LOCATION LOCATION/ANTENNA
These two points are actually more important than the type of radio you are using and they are strongly related. You can get the same reception in a bad place (with a good antenna) as in a good place (with a bad antenna)! But let’s work on improving both!
Statement from Radio Bob: You MUST have an antenna (of some kind) to receive any signals on a radio!
Another statement from Radio Bob: VHF radio waves travel more or less in straight lines. They are weakened by objects that get between the transmitter and receiver.
POSITION:
The closer you are to an NCPR transmitter (check out this map), the greater your chance of receiving a clear signal from NCPR.
The higher your antenna is located, the greater your chance of receiving a clear signal from NCPR. In other words, if your radio has a built-in antenna, it will work better in your attic than in your basement! Or if you have an outside antenna, it works better on the roof than on your kid’s old swing.
If your house is on a hill, you will have better reception than in a valley.
If there is a large object (e.g. a mountain) between your house and the NCPR transmitter, you are probably getting a bad signal!
If your antenna is outdoors, it will work better than indoors.
ANTENNA:
Someone once said that you MUST have an antenna to get any radio reception at all, and he/she was right! The cheapest radios ONLY have built-in antennas, with no provision for connecting an external antenna. With better radios, you have a choice.
A radio with a built-in antenna Built-in antennas: Even the lowest-end radio typically has a built-in antenna with typically poor performance. Most clock/table radios use the power cord as an antenna. A “Walkman” or iPod with FM radio uses the headphone cable as an antenna! Except in strong signal areas (near a transmitter), none of these work very well. Signals they receive are usually variable; For example, as you walk across the room, the signal strength will change (usually for the worse!). Here is a photo of a radio with an antenna built in:
Radio Bob recommends: If your radio has a built-in antenna and you’re almost happy with its performance, try moving the power cord around, it may work slightly better draped over the dresser rather than on the floor.
Wire Dipole (usually supplied with better radios): This is a flexible wire antenna that comes with some radios, including the few I’ve recommended before. Using this antenna will improve reception somewhat, but as with ALL antennas, this is not the perfect solution. It attaches to the back of the radio and then “hangs” somewhere in space as a “T” with the two ends as far apart as possible. (That’s the tricky part, because who wants unsightly wire pinned to the walls of their living room, not even me!) It’s also somewhat directional; It will (theoretically) pick up radio stations better perpendicular to the horizontal part of the “T”. So if you’re listening to multiple stations broadcasting from different directions, this might not be ideal. (You could try snaking the antenna out of a window and somehow tacking the “T” part outside to improve reception.)
Three antenna types: rabbit ears (top left); outward direction (top right); Outdoor Omnidirectional (bottom right) Telescoping Antenna(s)/”Bunny Ears”: Some “boomboxes” and portable radios have one or two telescoping antenna rods. These work a little better than the wire “dipoles” as you can move the one (or two) rods around for optimal performance. You can buy a pair of “bunny ears” from Radio Shack for about $10.
Radio Bob Tip: Don’t bother with other indoor antennas that DO NOT come with unsightly long poles. Round, ashtray-sized, and other types of indoor antennas are intended for UHF television and do not work very well with an FM radio.
Boosted Indoor Antennas: People ask me about these things every day (maybe every few months). and I guess my answer is something along the lines of “it all depends”. There are several available, made by Terk, Audiovox and others. They are dipole or similar antennas in an “attractive” case with a small preamp designed to boost the signal before it reaches your radio. Technically, there are several things wrong with this approach. Usually your radio already has a very good preamp built into its circuitry. A ‘dipole’ antenna connected to your radio should work just as well as a boosted antenna (unless your radio is somehow ‘received’!). there are strong FM stations in the neighborhood and you are trying to pick up a weak one!
On the other hand, if you can’t have an outdoor antenna and an indoor dipole or a pair of “bunny ears” is too unsightly, then a snazzy looking indoor antenna might be best for you. However, I don’t think it will “work wonders” with your FM reception. Let me know how they work for you. Email [email protected]
Outdoor Antennas: If you can somehow manage an outdoor antenna, this is the way to go! Apartment dwellers, renters, cave dwellers, submarine operators. I’m sorry as I know you probably can’t install an outside antenna.
The best thing for the rest of us is to use (or repurpose) a TV antenna that’s already on your roof. If you still use it to receive off-air TV, then get a cheap TV FM splitter. Or if you’ve switched to cable TV or satellite TV, simply connect your old TV connection to your FM radio. You will be surprised how well this works!
If you are looking to install a new outdoor FM antenna, there are two types to choose from, “Omnidirectional” and “Directional”. An Omni, like the Winegard HD-6010 ($20), receives FM signals from all directions. This is a decent choice if you like hopping from station to station.
If you only listen to one station most of the time (maybe NCPR?) or most of the stations you listen to are in (more or less) the same direction, or you could use an antenna “rotator” then you need a directional antenna. NCPR typically buys $800 for high-performance log periods like this pup, but you can almost as easily do it yourself with a Winegard HD-6000FM ($25).
Installing an outdoor antenna can be fun, challenging, or both! Here’s how:
The easiest way to do this is to hire someone to install it. Check the Yellow Pages or ask around.
To do it yourself, “somehow” mount your new VHF antenna to a metal tube. (You can get antenna towers in 5 and 10 foot lengths). Somehow attach the pipe to the roof or side of your house (remember, the higher the better!). Radio Shack has tripod roof mounts and wall mounts, as well as antenna masts. (Attention by the way!)
If the antenna is directional, point it towards the station of your choice (actually, it’s better to wait until the antenna connects to the radio, then manually rotate and lock the antenna for best reception). Or buy an antenna rotator with enough wire to connect it to the rotator controller that will be somewhere in your home.
Then you need to get the signal from your antenna to your radio somehow. In the “old” days, a flat cable about ½ inch wide called a “twin-lead” was all that was available. Now everyone uses a round coaxial cable. Your new antenna will likely have two screw terminals, so you will need a coaxial “balun” or matching transformer to connect to this type of antenna. The matching transformer has an “F” connector on the end away from the antenna. You can purchase coax cable with mating “F” connectors already installed, or use a special crimping tool and install your own “F” connectors on coax cables that you purchase separately.
Run the coaxial cable through the basement etc. to the radio. Newer radios also have an “F” connector and a switch labeled something like “internal” and “external”, connect the new wire from your new antenna to your radio, switch to “external” and listen More FM Stations Than You’ve Ever Heard!
INTERFERENCE: Wait! I didn’t mention any disorder! (Though as adults we should at least discuss it)
The atmosphere is FULL of high frequency signals, some of which conflict with each other. Here are a few examples of types of interference with NCPR that we’ve heard about.
Do cars need antennas?
Answer provided by. “That’s a great question, and not niche at all, since all cars do have them! The purpose of car antennas is to pick up radio signals, allowing you to listen to the radio. In newer vehicles, they can also pick up satellite radio stations or services, like Sirius XM.
How to Wire a Car Stereo to a 12v Battery
Car antennas work by picking up magnetic radio waves. When your antenna picks up the radio waves, your car’s radio receiver amplifies them so you can hear the station you want.
As with a regular radio or television antenna, if you move too far from the radio waves or broadcasts, you will hear noise.
If you have an antenna capable of receiving satellite radio, you won’t hear noise since it uses digital frequencies. In addition, you can listen to a variety of channels that are not normally available with traditional radio waves.”
MORE: Common auto insurance myths debunked
Does FM radio need an antenna?
Statement from Radio Bob: You MUST have an antenna (of some kind) to receive any signals on a radio! Another statement from Radio Bob: FM Radio Waves travel more-or-less in straight lines. They are weakened by objects that get between the transmitter and receiver.
How to Wire a Car Stereo to a 12v Battery
A good radio A good antenna A good location
If you have all three, you can potentially pick up an FM station up to 100 miles away! However, most of us only have one of these items at best
RADIOS: For good reception, a radio must have good selectivity (selectivity is a radio’s ability to separate weak, nearby, on the FM dial, strong stations) and good sensitivity (the ability to pick out weak, distant stations at all). to recieve!)
Car radios: You probably already have a radio with these functions. This radio is in your car. Car radios must be built to high standards to ensure decent reception in a moving vehicle over variable terrain and with a serious source of interference nearby (your engine!). Surely you’ve noticed that FM radio reception in your car is usually better than at home. This is partly because your car radio is probably better than your home radio.
Home/Office Radios: Most home radios have poor selectivity and sensitivity (we like to call them “junk” in the radio business). Typical $19.95 radios with analog tuning (as opposed to digital tuning, which shows the radio station’s frequency in illuminated numbers) will work, but only near a radio station’s transmitter. Most clock radios, under cupboard radios, “boom boxes”, crank radios, etc. just don’t work very well, especially when compared to a car stereo!
Boston Acoustics Horizon Solo
Boston Acoustics Horizon Duo
Tivoli Model One
Sangean WR-2
SONY XDR-F1HD
RadioBob recommends:
Ripping a car stereo out of a car, building a 12 volt DC power supply, building a really cool Honduran mahogany or purpleheart case, and finding some nice external speakers.
OK, seriously, there are some great radios out there, yes they cost more than a $19.95 disposable plastic radio, but they are MUCH better. They sound great and are a quality product. Today (early 2009) I would recommend the Boston Acoustics Horizon Solo clock/table radio for around $100. Or the stereo version (the Boston Acoustics Horizon Duo) for $150. Then there’s the Tivoli “Model One” if you don’t need a watch, and like a “retro” analog tuning wheel (around $140) or even the button-filled Sangean WR-2 (also around $140).
If you happen to have a component stereo system (typically separate amplifier/tuner with separate speakers), your tuner may already have decent sensitivity and selectivity. Try connecting a better antenna (see below) and see how your reception improves! If you’re looking to buy a state-of-the-art FM tuner (at a very reasonable price), get the SONY XDR-F1HD (under $100). Reviews have ranked this as one of the best tuners ever built! Remember that you must have an external amplifier and speakers for this!
ANTENNA/LOCATION LOCATION/ANTENNA ANTENNA/LOCATION LOCATION/ANTENNA
These two points are actually more important than the type of radio you are using and they are strongly related. You can get the same reception in a bad place (with a good antenna) as in a good place (with a bad antenna)! But let’s work on improving both!
Statement from Radio Bob: You MUST have an antenna (of some kind) to receive any signals on a radio!
Another statement from Radio Bob: VHF radio waves travel more or less in straight lines. They are weakened by objects that get between the transmitter and receiver.
POSITION:
The closer you are to an NCPR transmitter (check out this map), the greater your chance of receiving a clear signal from NCPR.
The higher your antenna is located, the greater your chance of receiving a clear signal from NCPR. In other words, if your radio has a built-in antenna, it will work better in your attic than in your basement! Or if you have an outside antenna, it works better on the roof than on your kid’s old swing.
If your house is on a hill, you will have better reception than in a valley.
If there is a large object (e.g. a mountain) between your house and the NCPR transmitter, you are probably getting a bad signal!
If your antenna is outdoors, it will work better than indoors.
ANTENNA:
Someone once said that you MUST have an antenna to get any radio reception at all, and he/she was right! The cheapest radios ONLY have built-in antennas, with no provision for connecting an external antenna. With better radios, you have a choice.
A radio with a built-in antenna Built-in antennas: Even the lowest-end radio typically has a built-in antenna with typically poor performance. Most clock/table radios use the power cord as an antenna. A “Walkman” or iPod with FM radio uses the headphone cable as an antenna! Except in strong signal areas (near a transmitter), none of these work very well. Signals they receive are usually variable; For example, as you walk across the room, the signal strength will change (usually for the worse!). Here is a photo of a radio with an antenna built in:
Radio Bob recommends: If your radio has a built-in antenna and you’re almost happy with its performance, try moving the power cord around, it may work slightly better draped over the dresser rather than on the floor.
Wire Dipole (usually supplied with better radios): This is a flexible wire antenna that comes with some radios, including the few I’ve recommended before. Using this antenna will improve reception somewhat, but as with ALL antennas, this is not the perfect solution. It attaches to the back of the radio and then “hangs” somewhere in space as a “T” with the two ends as far apart as possible. (That’s the tricky part, because who wants unsightly wire pinned to the walls of their living room, not even me!) It’s also somewhat directional; It will (theoretically) pick up radio stations better perpendicular to the horizontal part of the “T”. So if you’re listening to multiple stations broadcasting from different directions, this might not be ideal. (You could try snaking the antenna out of a window and somehow tacking the “T” part outside to improve reception.)
Three antenna types: rabbit ears (top left); outward direction (top right); Outdoor Omnidirectional (bottom right) Telescoping Antenna(s)/”Bunny Ears”: Some “boomboxes” and portable radios have one or two telescoping antenna rods. These work a little better than the wire “dipoles” as you can move the one (or two) rods around for optimal performance. You can buy a pair of “bunny ears” from Radio Shack for about $10.
Radio Bob Tip: Don’t bother with other indoor antennas that DO NOT come with unsightly long poles. Round, ashtray-sized, and other types of indoor antennas are intended for UHF television and do not work very well with an FM radio.
Boosted Indoor Antennas: People ask me about these things every day (maybe every few months). and I guess my answer is something along the lines of “it all depends”. There are several available, made by Terk, Audiovox and others. They are dipole or similar antennas in an “attractive” case with a small preamp designed to boost the signal before it reaches your radio. Technically, there are several things wrong with this approach. Usually your radio already has a very good preamp built into its circuitry. A ‘dipole’ antenna connected to your radio should work just as well as a boosted antenna (unless your radio is somehow ‘received’!). there are strong FM stations in the neighborhood and you are trying to pick up a weak one!
On the other hand, if you can’t have an outdoor antenna and an indoor dipole or a pair of “bunny ears” is too unsightly, then a snazzy looking indoor antenna might be best for you. However, I don’t think it will “work wonders” with your FM reception. Let me know how they work for you. Email [email protected]
Outdoor Antennas: If you can somehow manage an outdoor antenna, this is the way to go! Apartment dwellers, renters, cave dwellers, submarine operators. I’m sorry as I know you probably can’t install an outside antenna.
The best thing for the rest of us is to use (or repurpose) a TV antenna that’s already on your roof. If you still use it to receive off-air TV, then get a cheap TV FM splitter. Or if you’ve switched to cable TV or satellite TV, simply connect your old TV connection to your FM radio. You will be surprised how well this works!
If you are looking to install a new outdoor FM antenna, there are two types to choose from, “Omnidirectional” and “Directional”. An Omni, like the Winegard HD-6010 ($20), receives FM signals from all directions. This is a decent choice if you like hopping from station to station.
If you only listen to one station most of the time (maybe NCPR?) or most of the stations you listen to are in (more or less) the same direction, or you could use an antenna “rotator” then you need a directional antenna. NCPR typically buys $800 for high-performance log periods like this pup, but you can almost as easily do it yourself with a Winegard HD-6000FM ($25).
Installing an outdoor antenna can be fun, challenging, or both! Here’s how:
The easiest way to do this is to hire someone to install it. Check the Yellow Pages or ask around.
To do it yourself, “somehow” mount your new VHF antenna to a metal tube. (You can get antenna towers in 5 and 10 foot lengths). Somehow attach the pipe to the roof or side of your house (remember, the higher the better!). Radio Shack has tripod roof mounts and wall mounts, as well as antenna masts. (Attention by the way!)
If the antenna is directional, point it towards the station of your choice (actually, it’s better to wait until the antenna connects to the radio, then manually rotate and lock the antenna for best reception). Or buy an antenna rotator with enough wire to connect it to the rotator controller that will be somewhere in your home.
Then you need to get the signal from your antenna to your radio somehow. In the “old” days, a flat cable about ½ inch wide called a “twin-lead” was all that was available. Now everyone uses a round coaxial cable. Your new antenna will likely have two screw terminals, so you will need a coaxial “balun” or matching transformer to connect to this type of antenna. The matching transformer has an “F” connector on the end away from the antenna. You can purchase coax cable with mating “F” connectors already installed, or use a special crimping tool and install your own “F” connectors on coax cables that you purchase separately.
Run the coaxial cable through the basement etc. to the radio. Newer radios also have an “F” connector and a switch labeled something like “internal” and “external”, connect the new wire from your new antenna to your radio, switch to “external” and listen More FM Stations Than You’ve Ever Heard!
INTERFERENCE: Wait! I didn’t mention any disorder! (Though as adults we should at least discuss it)
The atmosphere is FULL of high frequency signals, some of which conflict with each other. Here are a few examples of types of interference with NCPR that we’ve heard about.
Do cars need antennas?
Answer provided by. “That’s a great question, and not niche at all, since all cars do have them! The purpose of car antennas is to pick up radio signals, allowing you to listen to the radio. In newer vehicles, they can also pick up satellite radio stations or services, like Sirius XM.
How to Wire a Car Stereo to a 12v Battery
Car antennas work by picking up magnetic radio waves. When your antenna picks up the radio waves, your car’s radio receiver amplifies them so you can hear the station you want.
As with a regular radio or television antenna, if you move too far from the radio waves or broadcasts, you will hear noise.
If you have an antenna capable of receiving satellite radio, you won’t hear noise since it uses digital frequencies. In addition, you can listen to a variety of channels that are not normally available with traditional radio waves.”
MORE: Common auto insurance myths debunked
What are antennas used for?
Antennas are used for both sending and receiving radio transmissions. Technologies such as radio and TV, mobile phones and Wi-Fi, connected cars, global positioning systems (GPS), space communications, radars etc. would not have been possible without antennas.
How to Wire a Car Stereo to a 12v Battery
What is an antenna?
Before we get anything technical, it’s always handy to define the topic.
An antenna is a device that converts alternating current (AC) to electromagnetic waves and vice versa.
The current and thus also the electromagnetic waves must change over time in order to be able to transport information.
Antennas were discovered by Heinrich Hertz in 1888.
For the first time he used an antenna to prove the existence of electromagnetic waves.
They are used in almost all electronic devices for civil, military and medical applications. Antennas are used for both sending and receiving radio transmissions.
Technologies such as radio and television, cell phones and Wi-Fi, connected cars, global positioning systems (GPS), space communications, radar, etc. would not have been possible without antennas.
How do antennas work?
The simplest and most common antenna is a dipole antenna.
A dipole is simply two wires of equal length connected to a receiver or transmitter at one end.
When an AC voltage is applied to the antenna, the electrical charges oscillate along the wire, alternating between positive and negative over time.
The electrical charges and the electrons that carry the charges (electric current) create magnetic and electrical waves that carry signals and information through air at the speed of light.
Vibration of charges on a dipole wire and generated electric fields.
The frequency with which the charged electrons change polarity along the antenna wire (the number of charge oscillations) per second defines the frequency of the dipole antenna. Frequency is measured in Hertz.
One hertz (Hz) equals one oscillation in one second.
To give you an idea, a Wi-Fi antenna changes polarity 2.4 billion times per second, hence its frequency is 2.4 GigaHertz (GHz).
Antenna size and length is a function of its operating frequency and wavelength. The lower the frequency, the longer the wavelength and the bigger the antenna.
4 dipoles at a radio station for transmission of radio/TV Semi-rigid wire dipole antenna
Antenna radiation pattern
The energy radiated from an antenna is represented by the radiation pattern of the antenna.
Radiation patterns are schematic representations of the distribution of radiated energy in space as a function of direction.
For example, the radiation pattern of the dipole antenna is said to be omnidirectional because the antenna radiates evenly in all directions around the wire.
The directions in which an antenna does not radiate are called nulls.
In other words, the antenna cannot receive a signal coming from the null directions.
Depending on the application, antennas have different radiation patterns.
A monopole antenna (similar to a dipole antenna, except that it has only one wire) mounted on a car to receive FM radio has an omnidirectional radiation pattern because the radio waves are expected to arrive from all directions.
Omnidirectional wire monopole antenna on a car for receiving FM radio
On the other hand, a dish antenna, e.g. A satellite dish used in satellite communications, has a directional radiation pattern. This means that the antenna only radiates in one direction and must be pointed in a certain direction in order to receive signals.
The radiation pattern of a parabolic satellite
antenna gain
The other important antenna property is antenna gain.
It describes how much power is radiated in a certain direction and is related to the radiation pattern of the antenna.
Since the antenna only emits a fixed amount of power, the gain of a dipole antenna is lower than that of a parabolic antenna.
The dipole antenna spreads radiation evenly in all directions, while a satellite dish concentrates antenna power in one direction, resulting in higher power (gain) in that direction.
Conclusion
Antennas are constantly evolving. As electronic devices become smaller and smarter, the need for small but efficient and inexpensive antennas is growing. This article only scratches the surface of the important topic of antennas. It is an overview of antennas, with some of the most common and most viewed antennas selected as examples.
David de Brouwer
Founder / Managing Director Engibex
diy turn car radio into garage radio or house radio
See some more details on the topic how to make a car radio work without antenna here:
This Is How To Make A Car Radio Work Without Antenna
Locate the ground wire among the network of cables at the back of the stereo. The ground wire is usually black. This wire powers up the CD player of your car …
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How To Make A Car Radio Work Without Antenna?
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how to make a car radio work without antenna? – [Answer] 2022
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This Is How To Make A Car Radio Work Without Antenna
A car without a radio makes every journey boring. While driving you have nothing to occupy your ears and mind.
Some cars have car radios but no antenna. What does this mean for such cars? You can’t use the radio.
But there are ways you can get your car stereo to work even without an antenna. You don’t need a technician to do it for you. Just read this article and follow the steps to get it done.
Are you ready? Let’s dive right in!
What a car antenna
Let’s face it, a car antenna is important. The antenna captures magnetic energy in radio waves, converts the wave, and transmits it to the radio to produce sound. It is a link between the radio waves and the radio itself.
Radio waves are emitted from a broadcasting station or transmitter. The car antenna attracts these waves and converts them into electrical charges. Then these small electrical charges are sent to the radio via the transmission line.
In addition, the small electrical charges are converted into sound energy/waves. This noise is what you hear from your radio when you turn it on. The antenna is crucial for the function of your car radio.
But even if the antenna is defective, you can get your car radio working again. Here’s how to do it.
Using the car chassis, Bluetooth connectivity (if your car stereo has Bluetooth capability), analog cable, FM transmitter and an Android phone.
How to make a car radio work without antenna with chassis
Metal makes up most of a car’s body. And you can use the metal body part of the car as an antenna by connecting the car radio to the chassis. Here are the following steps:
In order to connect your car radio to your car’s chassis, you need some tools to help you in the job.
These include screwdrivers, tape, wire cutters/pliers, coaxial connectors/butt connectors, etc.
Step 1 :
Carefully remove the car radio from the dashboard. You can achieve this by loosening the screws/bolts on the instrument panel that attach the radio to the dashboard. You can use the appropriate screwdriver for this task.
Dashboard design is not the same for all cars. So carefully walk around your dashboard to locate the studs, screws and joints. You don’t want to damage your stereo.
Step 2:
Locate the ground wire between the wiring network on the back of the stereo. The ground wire is usually black. This cable supplies power to the CD player in your car radio. And it connects the car’s metal chassis to the CD player. Cut off part of the black wire with a cutter.
Step 3:
Identify the Boundary Wire and cut off a section with the wire cutters/pliers to connect it to the ground wire. If your stereo does not have an antenna cable, please obtain one of a reasonable length.
With the insulated butt connectors you can connect ground and antenna cables. It’s better to use an insulated butt connector than a plastic strap connecting the ground and antenna wires.
Step 4:
Finally, reconnect your car stereo to its original position. Please turn on and search for frequency channels. You get some frequencies on your stereo.
The above steps are possible because the antenna cable has been connected to ground. And the bottom is connected to the chassis. The chassis uses the metal body of the car as an antenna.
How to make a car radio work with an Android phone without an antenna
If you find using chassis too technical, you can try the Android phone method. All you need is a smartphone and a car radio.
Most Android phones have Bluetooth connectivity features, FM radio, USB ports, and auxiliary ports. You can connect your smartphone to your car radio with any of the above Android phone features without the help of an antenna.
Turn on the car radio Bluetooth if it has one. Turn on the Bluetooth phone and on the other end, search for a new nearby device. Connect the phone to the radio.
After that, start the FM radio on your phone and select a frequency station. The car radio plays the same frequency station as your phone.
Without Bluetooth connectivity, you can use the auxiliary cable and connect the Android phone to the stereo. But you must set your radio to Auxiliary mode.
You can also use the USB port and FM transmitter with the help of your smartphone to play your car radio without an antenna.
In addition, the smartphone offers the possibility to play your favorite music. You can enjoy the video, MP4 files and 3GP if your car stereo has a screen and the function.
How to make a call through the car radio
You can use the car radio to make and receive calls on your cell phone while driving. All you need is the Bluetooth feature in the phone and in the car radio.
You can get hands-free kit if your stereo doesn’t have bluetooth function. Please follow these simple steps below:
Step #1: Turn on the car radio and your smartphone as both have Bluetooth properties.
Step #2: Enter your phone settings, find Bluetooth option and tap on it to open it. Please turn it on and search for Bluetooth nearby.
Step 3: Select the Bluetooth name of your car stereo or the name of your car kit as it appears on your phone and pair it. If the connection is successful, your stereo will emit a soft beep. Congratulations, you can now make and receive calls through your car stereo.
Some high-tech car radios also have voice commands. The explanation above allows for easy interaction with your phone through the stereo using the voice command.
Using a mobile phone while driving can distract the driver, which in turn can lead to an accident. Therefore, using a hands-free kit or Bluetooth connectivity can allow the driver to focus more on driving while talking through the radio speakers.
In some states it is illegal to hold the phone while driving. But in other states, it’s not a serious offense. Using your phone while driving as described above can save you from some legal hassles or fines.
How to improve car radio reception
You may notice an interruption in your stereo. In other cases, it may just be a static sound emanating from the stereo or interference of some frequencies.
Frequency interference can be caused by so many factors. The best thing to do is to improve car radio reception if there are constant frequency interruptions.
The first thing you can do to improve your signal strength is to check the antenna. It can significantly improve car radio reception, as simple as that may sound. Some antennas are retractable. Make sure you drag them all up to get a better signal.
Second, you can check if your antenna has a problem after extending it and the radio reception is still poor. Make sure the wire connection to the antenna is intact.
And watch out for rust at the base of the antenna; If present, replace the antenna. The antenna is the signal receiver. It must be good for the car radio to work well.
Also, you can check your car radio and make sure it is working properly. If you find any error, please replace the car radio. It is more economical to change the car radio than to repair it.
In addition, you can consult an electrician to check for possible car radio frequency interference with any part of the car.
Finally, radio frequencies are always interfered with in mountain and skyscraper regions due to physical barriers. There is little you can do if you cannot get out of such an environment. You can also use the transmitter amplifier to improve car radio reception in these areas.
Conclusion
The secret of a working car radio is the antenna. If the antenna does not pick up radio waves and transmit them to the stereo, your radio will not work. In addition, without an antenna, the car radio cannot play FM or AM modules.
Nevertheless, now you have learned how to make car stereo working without antenna using chassis method, FM transmitter, Android phone method, etc.
It’s up to you to implement one of the methods detailed in this article so that your car radio works without an antenna. So you can also enjoy your favorite station on the go.
Antenna (radio)
Electric device
“Antennas” redirects here. For other uses of “antenna”, see Antenna (disambiguation)
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents traveling in metal conductors used with a transmitter or receiver.[1] In transmission, a radio transmitter supplies electrical current to the terminals of the antenna, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). When receiving, an antenna intercepts part of the power of a radio wave to generate an electric current at its terminals, which is applied to a receiver for amplification. Antennas are essential components of all radio devices.[2]
An antenna is an arrangement of conductors (elements) that are electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves equally in all horizontal directions (omnidirectional antennas) or preferentially in a specific direction (directional or high-gain or “beam” antennas). An antenna may contain components not connected to the transmitter, parabolic reflectors, horns, or parasitic elements that serve to direct the radio waves into a beam or other desired radiation pattern. High directivity and good transmission efficiency are difficult to achieve with antennas with dimensions much smaller than half a wavelength.
The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of waves predicted by James Clerk Maxwell’s electromagnetic theory. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmission and reception. From 1895 Guglielmo Marconi began developing practical antennas for long-distance wireless telegraphy, for which he received a Nobel Prize.[4]
Terminology[edit]
Electronic symbol for an antenna
The words antenna and aerial are used interchangeably. Occasionally the equivalent term “antenna” is used to specifically denote an elevated horizontal wire antenna. The origin of the word antenna in the context of wireless devices is credited to Italian radio pioneer Guglielmo Marconi. In the summer of 1895, Marconi began testing his wireless system outdoors at his father’s estate near Bologna, and soon began experimenting with long wire “antennas” suspended from a pole.[4] In Italian, a tent pole is known as l’antenna centrale, and the pole with the wire was simply called l’antenna. Until then, wirelessly radiating transmitting and receiving elements were simply referred to as “terminals”. Because of his notoriety, Marconi’s use of the word antenna spread among wireless researchers and enthusiasts, and later the general public.
Antenna can broadly refer to an entire assembly that includes a support structure, housing (if any), etc., in addition to the actual functional components. A receiving antenna may contain not only the metal passive receiving elements, but also an integrated preamplifier or mixer, particularly at and above microwave frequencies.
Overview [ edit ]
Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field.[9] Radio waves are electromagnetic waves that carry signals through air (or space) at the speed of light with almost no transmission loss.
An automobile whip antenna, a common example of an omnidirectional antenna.
Antennas can be classified as omnidirectional, radiating energy approximately equally in all horizontal directions, or directional, concentrating radio waves in one or more directions. A so-called beam antenna is unidirectional and designed for maximum response in the direction of the other station, while many other antennas are designed to pick up stations in different directions but are not truly omnidirectional. Because antennas obey reciprocity, the same radiation pattern applies to both transmission and reception of radio waves. A hypothetical antenna that radiates equally at all vertical and horizontal angles is called an isotropic radiator, but these cannot exist in practice, nor would they be particularly desirable. Rather, for most terrestrial communications, there is an advantage in reducing radiation to the sky or to the ground in favor of the horizontal direction(s). A horizontally oriented dipole antenna does not transmit energy in the direction of the conductor – this is called the antenna null – but is usable in most other directions. A number of such dipole elements can be combined into an antenna array like the Yagi-Uda to favor a single horizontal direction, referred to as a beam antenna.
The dipole antenna, which forms the basis for most antenna designs, is a balanced component with equal but opposite voltages and currents applied to its two terminals. The vertical antenna is a monopole antenna that is not ground balanced. Ground (or any large conductive surface) plays the role of the second conductor of a dipole. Because monopole antennas rely on a conductive surface, they can be mounted with a ground plane to approximate the effect of mounting on the surface of the earth.
More complex antennas increase the directivity of the antenna. Additional elements in the antenna structure that do not have to be connected directly to the receiver or transmitter increase its directivity. The “gain” of the antenna describes the concentration of the radiated power in a specific solid angle. “Gain” is perhaps an unfortunate term compared to the amplifier’s “gain” which implies a net increase in performance. In contrast, with antenna “gain” the increased power in the desired direction comes at the expense of the decreased power in undesired directions. Unlike amplifiers, antennas are electrically “passive” devices that conserve total power, and there is no increase in total power beyond that supplied by the power source (the transmitter), only an improved distribution of that fixed total power.
A phased array consists of two or more simple antennas connected by an electrical network. These are often several parallel dipole antennas with a specific spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can be used as a “broadside array” (direction perpendicular to a line connecting the elements) or an “end-fire array” (direction along the line connecting the elements). ) work elements). Antenna arrays can use any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop, or slot antennas. These elements are often identical.
Logarithmic-periodic and frequency-independent antennas use self-similarity to be operable over a wide range of bandwidths. The best-known example is the log-periodic dipolar array, which can be thought of as a number (typically 10 to 20) connected dipole elements of progressive lengths in an endfire array, making it fairly directional; It is mainly used as a roof antenna for television reception. On the other hand, a Yagi-Uda (or simply “Yagi”) antenna with a somewhat similar appearance has only one dipole element with one electrical connection; the other parasitic elements interact with the electromagnetic field to realize a narrow bandwidth highly directional antenna.
An even greater directivity can be achieved with aperture antennas such as the parabolic reflector or the horn antenna. Since high directivity in an antenna depends on it being large compared to wavelength, highly directional (i.e., high gain) antennas become more practical at higher frequencies (UHF and higher).
At low frequencies (like AM broadcast), vertical tower arrays will be used to achieve directivity[10] and will occupy large land areas. A long Beverage antenna can have a significant directivity for reception. For omnidirectional portable use, a short vertical antenna or a small loop antenna works well, but the main design challenge is that of impedance matching. With a vertical antenna, a loading coil can be used at the base of the antenna to cancel the reactive component of the impedance; small loop antennas are tuned with parallel capacitors for this purpose.
An antenna feed is the transmission line or feeder line that connects the antenna to a transmitter or receiver. “Antenna feed” can refer to any component that connects the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In the case of a so-called “aperture antenna”, such as a horn or dish, “feed” can also refer to a basic radiating antenna embedded throughout the system of reflective elements (usually at the focus of the dish or at the neck of a horn) , which could be considered as the only active element in this antenna system. Instead of a (conductive) transmission line, a microwave antenna can also be fed directly from a waveguide.
An antenna counterpoise or ground plane is a structure of conductive material that enhances or replaces grounding. It can be connected to the natural soil or isolated from it. With a monopole antenna, this assists in the functioning of the natural soil, particularly where variations (or limitations) in the properties of the natural soil affect its proper functioning. Such a structure is usually connected to the return connection of an unbalanced transmission line, such as the shield of a coaxial cable.
An electromagnetic wave refractor in some plane antennas is a component that, by virtue of its shape and position, serves to selectively retard or advance portions of the electromagnetic wavefront passing through it. The refractor changes the spatial properties of the wave on one side relative to the other side. For example, it may focus the wave or otherwise alter the wavefront, generally to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.
An antenna coupling network is a passive network (generally a combination of inductive and capacitive circuit elements) used for impedance matching between the antenna and the transmitter or receiver. This can be used to minimize losses on the feeder line by reducing the VSWR of the transmission line and to provide the transmitter or receiver with a standard resistive impedance required for its optimal operation. The feed point location(s) is/are selected and antenna elements electrically similar to tuner components can be built into the antenna structure itself to improve matching.
reciprocity[edit]
It is a fundamental property of antennas that the electrical characteristics of an antenna, such as gain, radiation pattern, impedance, bandwidth, resonant frequency, and polarization described in the next section, are the same whether the antenna is transmitting or receiving.[11] [12] For example, the “reception pattern” (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is operating and acting as a radiator. This is a consequence of the reciprocity theorem in electromagnetics.[12] Therefore, when discussing antenna characteristics, no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.
A necessary condition for the above reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral) means that the material responds to an electric current or magnetic field in one direction in the same way as it does to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as insulators and circulators made of non-reciprocal materials such as ferrite. These can be used to give the antenna a different behavior when receiving than when transmitting,[11] which can be useful in applications such as radar.
Resonant antennas[ edit ]
Most antenna designs are based on the principle of resonance. This is due to the behavior of moving electrons reflected off surfaces where the dielectric constant changes, similar to how light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, usually a thin metal wire or rod, which in the simplest case has a feed point at one end where it is connected to a transmission line. The conductor or element is aligned with the electric field of the desired signal, which usually means perpendicular to the line from antenna to source (or receiver in the case of a broadcast antenna).[13]
The electrical component of the radio signal induces a voltage in the conductor. As a result, an electric current begins to flow in the direction of the instantaneous field of the signal. When the resulting current reaches the end of the conductor, it is reflected, which corresponds to a phase change of 180 degrees. If the conductor is 1⁄4 of a wavelength long, the current will experience a 90 degree phase change from the point of injection until it reaches the end of the conductor, will be reflected 180 degrees, and then another 90 degrees on the way back. That means it has undergone a total of 360 degrees of phase change, bringing it back to the original signal. The current in the element thus adds to the current that is being produced by the source at that moment. This process creates a standing wave in the conductor with the maximum current at the feed.
The common half-wave dipole is probably the most common antenna design. This consists of two 1⁄4 wavelength elements arranged end-to-end and lying essentially along the same axis (or collinear), each feeding one side of a two-wire transmission cable. The physical arrangement of the two elements puts them 180 degrees out of phase, meaning that at any instant one of the elements is driving current into the transmission line while the other is pulling it out. The monopole antenna is essentially one-half of the half-wave dipole, a single 1⁄4-wavelength element with the other side connected to ground or an equivalent ground plane (or counterpoise). Monopoles, half the size of a dipole, are common for longwave radio signals where a dipole would be impractically large. Another common design is the folded dipole, which consists of two (or more) half-wave dipoles placed side by side and connected at their ends, but only one of which is driven.
The standing waveforms with this desired pattern at the design operating frequency f o , and antennas are usually designed for this size. However, feeding this element with 3 f 0 (whose wavelength is 1⁄3 that of f o) also results in a standing wave pattern. Thus, an antenna element is also resonant if its length is 3⁄4 of a wavelength. This applies to all odd multiples of 1/4 wavelength. This allows for some design flexibility in terms of antenna lengths and feed points. It is known that antennas used in this way are operated harmonically. Resonant antennas typically use a linear conductor (or element) or pair of such elements, each about a quarter wavelength long (odd multiples of quarter wavelengths are also resonant). Antennas which must be small compared to wavelength sacrifice efficiency and cannot be very directional. Because the wavelengths at higher frequencies (UHF, microwaves) are so small, there is usually no need to constrain the power to get a smaller physical size.
red for voltage, V, and blue for current, I), whose width is proportional to the amplitude of the quantity at that point on the antenna. Standing waves on a half-wave dipole operated at its resonant frequency. The waves are represented graphically by color bars (and) whose width is proportional to the amplitude of the quantity at that point on the antenna.
Current and voltage distribution[ edit ]
The quarter-wave elements mimic a series resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and a voltage node (minimum) at the feed. In electrical terms, this means that the element has minimal reactance and produces the maximum current at the minimum voltage. This is the ideal situation, because it brings maximum output with minimum input and thus the highest possible efficiency. In contrast to an ideal (lossless) series resonant circuit, there remains a finite resistance (corresponding to the relatively small voltage at the feed point) due to the radiation resistance of the antenna and any actual electrical losses.
Remember that when the electrical properties of the material change, a current is reflected. In order to efficiently transmit the received signal into the transmission line, it is important that the transmission line has the same impedance as its connection point on the antenna, otherwise part of the signal will be reflected backwards into the antenna body; Also, some of the transmitter’s signal power is reflected back to the transmitter when the electrical impedance changes at the junction of the feeder line and the antenna. This leads to the concept of impedance matching, the design of the overall antenna and transmission line system to keep the impedance as close as possible, thereby reducing these losses. Impedance matching is achieved by a circuit called an antenna tuner or impedance matching network between the transmitter and the antenna. The impedance match between feedline and antenna is measured by a parameter called the standing wave ratio (SWR) on the feedline.
Consider a half-wave dipole designed for signals with a wavelength of 1m, which means the antenna would be about 50cm long from tip to tip. If the element has a length to diameter ratio of 1000, it has an inherent impedance of about 63 ohms ohmic. Using the appropriate transmission cable or balun, we match this resistance to ensure minimal signal reflection. Driving this antenna with a current of 1 ampere requires 63 volts and the antenna radiates 63 watts (discounting losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; In this case, the current induced by the signal would arrive at the feed point of the antenna out of phase with the signal, causing the net current to drop while the voltage remains the same. Electrically, this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance and the signal is reflected back into the antenna, reducing performance. This could be addressed by changing the matching system between the antenna and the transmission line, but this solution only works well at the new design frequency.
The result is that the resonant antenna will only efficiently inject a signal into the transmission line if the frequency of the source signal is near the antenna’s design frequency or one of the resonance multiples. This makes resonant antenna designs inherently narrow band: only useful for a small frequency range centered around the resonance(s).
Electrically short antennas
It is possible to use simple impedance matching techniques to allow the use of monopole or dipole antennas that are much shorter than the 1/4 or 1/2 wave, respectively, at which they are resonant. When these antennas are made shorter (for a given frequency), their impedance becomes dominated by capacitive (negative) series reactance; By adding an appropriately sized “loading coil” – a series inductor of equal and opposite (positive) reactance – the antenna’s capacitive reactance can be canceled, leaving only pure resistance.
Sometimes the resulting (lower) electrical resonant frequency of such a system (antenna plus matching network) is described using the concept of electrical length, so an antenna used at a lower frequency than its resonant frequency is called an electrically short antenna.
For example, at 30MHz (10m wavelength) a true resonant 1/4 wave monopole would be nearly 2.5 meters long and using an antenna only 1.5 meters high would require the addition of a charging coil. Then it can be said that the coil lengthened the antenna to reach an electrical length of 2.5 meters. However, the resulting resistive impedance is quite a bit lower than that of a true 1/4 wave (resonant) monopole, often requiring further impedance matching (a transformer) to the desired transmission line. For increasingly shorter antennas (requiring greater “electrical lengthening”), the radiation resistance (roughly equal to the square of the antenna length) decreases, so the mismatch deteriorates due to a net reactance away from electrical resonance. Or one could also say that the equivalent resonant circuit of the antenna system has a higher Q-factor and thus a reduced bandwidth[16] which can even become insufficient for the spectrum of the transmitted signal. Resistive losses due to the charging coil relative to reduced radiation resistance result in reduced electrical efficiency, which can be of great concern for a transmitting antenna, but bandwidth is the main factor that sets the size of antennas at 1MHz and lower frequencies.
Arrays and reflectors[ edit ]
Yagi-Uda and log-periodic (“fishbone”) array antennas like this stack are commonly used at VHF and UHF frequencies.
The radiation flux depending on the distance to the transmitting antenna changes according to the distance law, since this describes the geometric divergence of the transmitted wave. For a given incoming flux, the power detected by a receiving antenna is proportional to its effective area. This parameter compares the power captured by a receiving antenna to the flux of an incoming wave (measured as the power density of the signal in watts per square meter). A half-wave dipole has an effective area of about 0.13λ2 seen from the broadside direction. If higher gain is needed, one cannot simply make the antenna larger. Due to the limitation of the effective range of a receiving antenna described below, it can be seen that with an already efficient antenna design, the only way to increase the gain (effective range) is to reduce the gain of the antenna in another direction.
When a half-wave dipole is not connected to an external circuit, but is instead shorted at the feed point, it becomes a half-wave resonant element, efficiently generating a standing wave in response to an incident radio wave. Since there is no load to absorb that power, it transmits all of the power, possibly with a phase shift that depends critically on the exact length of the element. Thus, such a conductor can be arranged to carry a second copy of a transmitter signal to affect the radiation pattern (and feed point impedance) of the element electrically connected to the transmitter. Antenna elements used in this way are called passive radiators.
A Yagi-Uda array uses passive elements to greatly increase gain in one direction (at the expense of other directions). A number of parallel approximately half-wave elements (of definite lengths) are arranged parallel to each other at definite positions along a cantilever; the boom is for support only and is not involved electrically. Only one of the elements is electrically connected to the transmitter or receiver, while the remaining elements are passive. The Yagi produces a fairly large gain (depending on the number of passive elements) and is often used as a directional antenna with an antenna rotor to control the direction of its beam. It suffers from a fairly limited bandwidth, limiting its use to specific applications.
Instead of using a driven antenna element along with passive radiators, one can build an array antenna where multiple elements are all driven in relative phases by the transmitter through a system of power dividers and transmission lines to concentrate the RF power in a single direction . In addition, a phased array can be made “steerable”, that is, by changing the phases applied to each element, the radiation pattern can be shifted without physically moving the antenna elements. Another common array antenna is the log-periodic dipole array, which is similar in appearance to the Yagi (having a number of parallel elements along a cantilever) but is entirely different in operation, with all elements having a phase inversion electrically connected to the adjacent element are connected ; Using the logarithmic-periodic principle, it acquires the unique property of maintaining its performance characteristics (gain and impedance) over a very wide bandwidth.
When a radio wave hits a large conductive plate, it is reflected (with the phase of the electric field reversed) just like a mirror reflects light. Placing such a reflector behind an otherwise omnidirectional antenna ensures that power that would have gone in its direction is redirected in the desired direction, increasing antenna gain by at least a factor of 2. Likewise, a corner reflector can ensure that all the power of the antenna is concentrated in just one quadrant of space (or less), resulting in an increase in gain. In practice, the reflector does not have to be solid sheet metal, but can consist of a curtain of rods aligned with the polarization of the antenna; This significantly reduces the weight and wind load of the reflector. The specular reflection of radio waves is also used in a parabolic reflector antenna, in which a curved reflecting surface causes an incoming wave to be focused to a so-called feed antenna; this results in an antenna system with an effective area comparable to the size of the reflector itself. Other concepts from geometric optics are also used in antenna technology, for example in the lens antenna.
Properties[ edit ]
The power gain (or simply “gain”) of the antenna also takes into account the efficiency of the antenna and is often the primary figure of merit. Antennas are characterized by a set of performance measurements that a user would be concerned with when selecting or designing an antenna for a particular application. A diagram of the directional characteristics in the space surrounding the antenna is its radiation pattern.
bandwidth [edit]
The frequency range or bandwidth over which an antenna works well can be very wide (like a log-periodic antenna) or narrow (like a small loop antenna); Outside this range, the antenna impedance becomes a poor match to the transmission line and the transmitter (or receiver). Using the antenna far from its design frequency will affect its radiation pattern and reduce its directivity gain.
In general, an antenna does not have a feedpoint impedance equal to that of a transmission line; A matching network between antenna ports and the transmission line improves power transfer to the antenna. Ein nicht einstellbares Anpassungsnetzwerk wird höchstwahrscheinlich die nutzbare Bandbreite des Antennensystems weiter einschränken. Es kann wünschenswert sein, röhrenförmige Elemente anstelle von dünnen Drähten zu verwenden, um eine Antenne herzustellen; diese ermöglichen eine größere Bandbreite. Oder mehrere dünne Drähte können in einem Käfig gruppiert werden, um ein dickeres Element zu simulieren. Dies erweitert die Bandbreite der Resonanz.
Amateurfunkantennen, die auf mehreren Frequenzbändern arbeiten, die weit voneinander entfernt sind, können Elemente, die auf diesen verschiedenen Frequenzen resonant sind, parallel verbinden. Die meiste Leistung des Senders fließt in das Resonanzelement, während die anderen eine hohe Impedanz aufweisen. Eine andere Lösung verwendet Fallen, parallele Resonanzkreise, die strategisch in Unterbrechungen platziert werden, die in langen Antennenelementen erzeugt werden. Wenn sie bei der speziellen Resonanzfrequenz der Falle verwendet wird, stellt die Falle eine sehr hohe Impedanz (Parallelresonanz) dar, wodurch das Element an der Stelle der Falle wirksam abgeschnitten wird; bei korrekter Positionierung bildet das abgeschnittene Element eine geeignete Resonanzantenne bei der Fallenfrequenz. Bei wesentlich höheren oder niedrigeren Frequenzen ermöglicht die Falle, dass die volle Länge des gebrochenen Elements verwendet wird, jedoch mit einer Resonanzfrequenz, die um die durch die Falle hinzugefügte Nettoreaktanz verschoben ist.
Die Bandbreiteneigenschaften eines resonanten Antennenelements können gemäß seinem Q charakterisiert werden, wobei der betroffene Widerstand der Strahlungswiderstand ist, der die Emission von Energie von der resonanten Antenne in den freien Raum darstellt.
Das Q einer Schmalbandantenne kann bis zu 15 betragen. Andererseits ist die Reaktanz bei der gleichen Off-Resonanzfrequenz einer Antenne mit dicken Elementen viel geringer, was folglich zu einem Q von nur 5 führt. Diese beiden Antennen kann bei der Resonanzfrequenz äquivalent funktionieren, aber die zweite Antenne wird über eine Bandbreite arbeiten, die dreimal so breit ist wie die Antenne, die aus einem dünnen Leiter besteht.
Antennen zur Verwendung über viel breitere Frequenzbereiche werden unter Verwendung weiterer Techniken erzielt. Durch die Anpassung eines Anpassungsnetzwerks kann im Prinzip jede Antenne auf jede Frequenz angepasst werden. Daher hat die in den meisten AM-Rundfunkempfängern (Mittelwelle) eingebaute kleine Schleifenantenne eine sehr schmale Bandbreite, wird jedoch unter Verwendung einer parallelen Kapazität abgestimmt, die entsprechend der Empfängerabstimmung eingestellt wird. Andererseits sind logarithmisch periodische Antennen nicht bei einer einzelnen Frequenz resonant, sondern können (im Prinzip) so gebaut werden, dass sie über jeden Frequenzbereich ähnliche Eigenschaften (einschließlich Speisepunktimpedanz) erreichen. Diese werden daher üblicherweise (in Form von gerichteten logarithmisch-periodischen Dipolarrays) als Fernsehantennen verwendet.
Gewinnen [ bearbeiten ]
Die Verstärkung ist ein Parameter, der den Grad der Richtwirkung des Strahlungsmusters der Antenne misst. Eine Antenne mit hoher Verstärkung strahlt den größten Teil ihrer Leistung in eine bestimmte Richtung ab, während eine Antenne mit niedriger Verstärkung über einen weiten Winkel strahlt. Der Antennengewinn oder Leistungsgewinn einer Antenne ist definiert als das Verhältnis der Intensität (Leistung pro Flächeneinheit), die von der Antenne in Richtung ihrer maximalen Leistung in einer beliebigen Entfernung abgestrahlt wird, geteilt durch die Intensität I iso {\displaystyle I_{\text{iso}}}, die in gleicher Entfernung von einer hypothetischen isotropen Antenne abgestrahlt wird, die in alle Richtungen die gleiche Leistung abstrahlt. Dieses dimensionslose Verhältnis wird normalerweise logarithmisch in Dezibel ausgedrückt, diese Einheiten werden als Dezibel-Isotrop (dBi) bezeichnet.
G dBi = 10 log ich ich iso {\displaystyle G_{\text{dBi}}=10\log {ich \over I_{\text{iso}}}\,}
Eine zweite Einheit zur Messung des Gewinns ist das Verhältnis der von der Antenne abgestrahlten Leistung zu der von einer Halbwellendipolantenne abgestrahlten Leistung. I dipole {\displaystyle I_{\text{dipole}}} ; diese Einheiten heißen Dezibel-Dipol (dBd)
G dBd = 10 log I I dipole {\displaystyle G_{\text{dBd}}=10\log {I \over I_{\text{dipole}}}\,}
Since the gain of a half-wave dipole is 2.15 dBi and the logarithm of a product is additive, the gain in dBi is just 2.15 decibels greater than the gain in dBd
G dBi ≈ G dBd + 2.15 {\displaystyle G_{\text{dBi}}\approx G_{\text{dBd}}+2.15\,}
High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at the other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones. Antenna gain should not be confused with amplifier gain, a separate parameter measuring the increase in signal power due to an amplifying device placed at the front-end of the system, such as a low-noise amplifier.
Effective area or aperture [ edit ]
The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which the antenna delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 Watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts RMS at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.
Due to reciprocity (discussed above) the gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss, that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency is equal to 1. Therefore, the effective area A eff in terms of the gain G in a given direction is given by:
A e f f = λ 2 4 π G {\displaystyle A_{\mathrm {eff} }={\lambda ^{2} \over 4\pi }\,G}
For an antenna with an efficiency of less than 100%, both the effective area and gain are reduced by that same amount. Therefore, the above relationship between gain and effective area still holds. These are thus two different ways of expressing the same quantity. A eff is especially convenient when computing the power that would be received by an antenna of a specified gain, as illustrated by the above example.
Radiation pattern [ edit ]
Polar plots of the horizontal cross sections of a (virtual) Yagi-Uda-antenna. Outline connects points with 3 dB field power compared to an ISO emitter.
The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles in the far-field. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called an omnidirectional pattern and when plotted looks like a torus or donut.
The radiation of many antennas shows a pattern of maxima or “lobes” at various angles, separated by “nulls”, angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant points in phase, and zero radiation at other angles where the radio waves arrive out of phase. In a directional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the “main lobe”. The other lobes usually represent unwanted radiation and are called “sidelobes”. The axis through the main lobe is called the “principal axis” or “boresight axis”.
The polar diagrams (and therefore the efficiency and gain) of Yagi antennas are tighter if the antenna is tuned for a narrower frequency range, e.g. the grouped antenna compared to the wideband. Similarly, the polar plots of horizontally polarized yagis are tighter than for those vertically polarized.[17]
Field regions [ edit ]
The space surrounding an antenna can be divided into three concentric regions: The reactive near-field (also called the inductive near-field), the radiating near-field (Fresnel region) and the far-field (Fraunhofer) regions. These regions are useful to identify the field structure in each, although the transitions between them are gradual, and there are no precise boundaries.
The far-field region is far enough from the antenna to ignore its size and shape: It can be assumed that the electromagnetic wave is purely a radiating plane wave (electric and magnetic fields are in phase and perpendicular to each other and to the direction of propagation). This simplifies the mathematical analysis of the radiated field.
Efficiency [ edit ]
Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna’s conductors, or loss between the reflector and feed horn of a parabolic antenna.
Antenna efficiency is separate from impedance matching, which may also reduce the amount of power radiated using a given transmitter. If an SWR meter reads 150 W of incident power and 50 W of reflected power, that means 100 W have actually been absorbed by the antenna (ignoring transmission line losses). How much of that power has actually been radiated cannot be directly determined through electrical measurements at (or before) the antenna terminals, but would require (for instance) careful measurement of field strength. The loss resistance and efficiency of an antenna can be calculated once the field strength is known, by comparing it to the power supplied to the antenna.
The loss resistance will generally affect the feedpoint impedance, adding to its resistive component. That resistance will consist of the sum of the radiation resistance R rad and the loss resistance R loss . If a current I is delivered to the terminals of an antenna, then a power of I2 R rad will be radiated and a power of I2 R loss will be lost as heat. Therefore, the efficiency of an antenna is equal to R rad /(R rad + R loss ). Only the total resistance R rad + R loss can be directly measured.
According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to its efficiency as a transmitting antenna, described above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance. At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).
Antennas which are not a significant fraction of a wavelength in size are inevitably inefficient due to their small radiation resistance. AM broadcast radios include a small loop antenna for reception which has an extremely poor efficiency. This has little effect on the receiver’s performance, but simply requires greater amplification by the receiver’s electronics. Contrast this tiny component to the massive and very tall towers used at AM broadcast stations for transmitting at the very same frequency, where every percentage point of reduced antenna efficiency entails a substantial cost.
The definition of antenna gain or power gain already includes the effect of the antenna’s efficiency. Therefore, if one is trying to radiate a signal toward a receiver using a transmitter of a given power, one need only compare the gain of various antennas rather than considering the efficiency as well. This is likewise true for a receiving antenna at very high (especially microwave) frequencies, where the point is to receive a signal which is strong compared to the receiver’s noise temperature. However, in the case of a directional antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the antenna efficiency, as discussed above. In this case, rather than quoting the antenna gain, one would be more concerned with the directive gain, or simply directivity which does not include the effect of antenna (in)efficiency. The directive gain of an antenna can be computed from the published gain divided by the antenna’s efficiency. In equation form, gain = directivity × efficiency.
Polarization [ edit ]
The orientation and physical structure of an antenna determine the polarization of the electric field of the radio wave transmitted by it. For instance, an antenna composed of a linear conductor (such as a dipole or whip antenna) oriented vertically will result in vertical polarization; if turned on its side the same antenna’s polarization will be horizontal.
Reflections generally affect polarization. Radio waves reflected off the ionosphere can change the wave’s polarization. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Using a vertically polarized antenna to receive a horizontally polarized wave (or visa-versa) results in relatively poor reception.
An antenna’s polarization can sometimes be inferred directly from its geometry. When the antenna’s conductors viewed from a reference location appear along one line, then the antenna’s polarization will be linear in that very direction. In the more general case, the antenna’s polarization must be determined through analysis. For instance, a turnstile antenna mounted horizontally (as is usual), from a distant location on earth, appears as a horizontal line segment, so its radiation received there is horizontally polarized. But viewed at a downward angle from an airplane, the same antenna does not meet this requirement; in fact its radiation is elliptically polarized when viewed from that direction. In some antennas the state of polarization will change with the frequency of transmission. The polarization of a commercial antenna is an essential specification.
In the most general case, polarization is elliptical, meaning that over each cycle the electric field vector traces out an ellipse. Two special cases are linear polarization (the ellipse collapses into a line) as discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates along one direction. In circular polarization, the electric field of the radio wave rotates around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the “thumb in the direction of the propagation” rule. Note that for circular polarization, optical researchers use the opposite right hand rule[citation needed] from the one used by radio engineers.
It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Otherwise there will be a loss of signal strength: when a linearly polarized antenna receives linearly polarized radiation at a relative angle of θ, then there will be a power loss of cos2θ. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations, suffering a 3 dB signal reduction. However it will be blind to a circularly polarized signal of the opposite orientation.
Impedance matching [ edit ]
Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not exactly correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 Ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive, but a transmitter (and some receivers) may have limited additional adjustments to cancel a certain amount of reactance, in order to “tweak” the match.
When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and nearly the same as the characteristic impedance of that transmission line, in addition to matching the impedance that the transmitter (or receiver) expects. The match is sought to minimize the amplitude of standing waves (measured via the standing wave ratio; SWR) that a mismatch raises on the line, and the increase in transmission line losses it entails.
Antenna tuning at the antenna [ edit ]
Antenna tuning, in the strict sense of modifying the antenna itself, generally refers only to cancellation of any reactance seen at the antenna terminals, leaving only a resistive impedance which might or might not be exactly the desired impedance (that of the transmission line).
Although an antenna may be designed to have a purely resistive feedpoint impedance (such as a dipole 97% of a half wavelength long) this might not be exactly true at the frequency that it is eventually used at. In most cases, in principle the physical length of the antenna can be “trimmed” to obtain a pure resistance, although this is rarely convenient. On the other hand, the addition of a contrary inductance or capacitance can be used to cancel a residual capacitive or inductive reactance, respectively, and may be more convenient than lowering the antenna.
Antenna reactance may be removed using lumped elements, such as capacitors or inductors in the main path of current traversing the antenna, often near the feedpoint, or by incorporating capacitive or inductive structures into the conducting body of the antenna to cancel the feedpoint reactance – such as open-ended “spoke” radial wires, or looped parallel wires – hence genuinely tune the antenna to resonance. In addition to those reactance-neutralizing add-ons, antennas of any kind may include a balun at their feedpoint to transform the resistive part of the impedance to more nearly match the feedline’s characteristic impedance.
Line matching at the radio [ edit ]
Antenna tuning in the loose sense, performed by an impedance matching device (somewhat inappropriately named an “antenna tuner”, or the older, more appropriate term transmatch) goes beyond merely removing reactance and includes transforming the remaining resistance to match the feedline and radio.
An additional problem is matching the remaining resistive impedance to the characteristic impedance of the transmission line: A general impedance matching network (an “antenna tuner” or ATU) will have at least two adjustable elements to correct both components of impedance. Any matching network will have both power losses and power restrictions when used for transmitting.
Commercial antennas are generally designed to approximately match standard 50 Ohm coaxial cables, at standard frequencies; the design expectation is that a matching network will be merely used to ‘tweak’ any residual mismatch.
Extreme examples of loaded small antennas [ edit ]
In some cases matching is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation.
Small vertical “whip”
For instance, for practical reasons a “whip antenna” can be made significantly shorter than a quarter-wavelength and then resonated, using a so-called loading coil.
The physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that the short vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; although, without further measures, the resistance will be somewhat lower than would be desired to match commercial coax.[citation needed]
Small “magnetic” loop
Another extreme case of impedance matching occurs when using a small loop antenna (usually, but not always, for receiving) at a relatively low frequency, where it appears almost as a pure inductor. Resonating such an inductor with a capacitor at the frequency of operation not only cancels the reactance (but when resonated via a parallel capacitor) greatly magnifies the very small radiation resistance of a small loop to produce a better-matched feedpoint impedance.[citation needed]
This is implemented in most AM broadcast receivers, with a small loop antenna wound around a ferrite rod (a “loopstick” antenna), resonated by a capacitor which is varied simultaneously with tuning the receiver to a new frequency, in order to maintain antenna resonance over the AM broadcast band
Effect of ground [ edit ]
Ground reflections is one of the common types of multipath.[18][19][20]
The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna’s height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.
When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave’s power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave’s angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.
For very low frequencies to high frequencies (< 30 MHz), the ground behaves as a lossy dielectric,[21] thus the ground is characterized both by a conductivity[22] and permittivity (dielectric constant) which can be measured for a given soil (but is influenced by fluctuating moisture levels) or can be estimated from certain maps. At lower mediumwave frequencies the ground acts mainly as a good conductor, which AM broadcast (0.5–1.7 MHz) antennas depend on. At frequencies between 3–30 MHz, a large portion of the energy from a horizontally polarized antenna reflects off the ground, with almost total reflection at the grazing angles important for ground wave propagation. That reflected wave, with its phase reversed, can either cancel or reinforce the direct wave, depending on the antenna height in wavelengths and elevation angle (for a sky wave). On the other hand, vertically polarized radiation is not well reflected by the ground except at grazing incidence or over very highly conducting surfaces such as sea water.[23] However the grazing angle reflection important for ground wave propagation, using vertical polarization, is in phase with the direct wave, providing a boost of up to 6 dB, as is detailed below. The wave reflected by earth can be considered as emitted by the image antenna. At VHF and above (> 30 MHz) the ground becomes a poorer reflector. However, for shortwave frequencies, especially below ~15 MHz, it remains a good reflector especially for horizontal polarization and grazing angles of incidence. That is important as these higher frequencies usually depend on horizontal line-of-sight propagation (except for satellite communications), the ground then behaving almost as a mirror.
The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, the dominant regime is that of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.
Whenever both the receiving or transmitting antenna are placed at significant heights above the ground (relative to the wavelength), waves reflected specularly by the ground will travel a longer distance than direct waves, inducing a phase shift which can sometimes be significant. When a sky wave is launched by such an antenna, that phase shift is always significant unless the antenna is very close to the ground (compared to the wavelength).
The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n ≈ 2) compared to air (n = 1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of π radians, or 180°). On the other hand, the vertical component of the wave’s electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modeled as a good electrical conductor.
The currents in an antenna appear as an image in opposite phase when reflected at grazing angles. This causes a phase reversal for waves emitted by a horizontally polarized antenna (center) but not for a vertically polarized antenna (left).
This means that a receiving antenna “sees” an image of the emitting antenna but with ‘reversed’ currents (opposite in direction and phase) if the emitting antenna is horizontally oriented (and thus horizontally polarized). However, the received current will be in the same absolute direction and phase if the emitting antenna is vertically polarized.
The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna’s impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna’s proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna’s impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna’s height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna’s impedance.
The ground reflection has an important effect on the net far field radiation pattern in the vertical plane, that is, as a function of elevation angle, which is thus different between a vertically and horizontally polarized antenna. Consider an antenna at a height h above the ground, transmitting a wave considered at the elevation angle θ. For a vertically polarized transmission the magnitude of the electric field of the electromagnetic wave produced by the direct ray plus the reflected ray is:
| E V | = 2 | E 0 | | cos ( 2 π h λ sin θ ) | {\displaystyle \textstyle {\left|E_{V}\right|=2\left|E_{0}\right|\,\left|\cos \left({2\pi h \over \lambda }\sin \theta \right)\right|}}
Thus the power received can be as high as 4 times that due to the direct wave alone (such as when θ = 0), following the square of the cosine. The sign inversion for the reflection of horizontally polarized emission instead results in:
| E H | = 2 | E 0 | | sin ( 2 π h λ sin θ ) | {\displaystyle \textstyle {\left|E_{H}\right|=2\left|E_{0}\right|\,\left|\sin \left({2\pi h \over \lambda }\sin \theta \right)\right|}}
where:
E 0 {\displaystyle \scriptstyle {E_{0}}}
θ is the elevation angle of the wave being considered.
is the elevation angle of the wave being considered. λ {\displaystyle \scriptstyle {\lambda }} wavelength.
wavelength. h {\displaystyle \scriptstyle {h}}
Radiation patterns of antennas and their images reflected by the ground. At left the polarization is vertical and there is always a maximum for θ = 0 . If the polarization is horizontal as at right, there is always a zero for θ = 0 .
For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by the direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ = 0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5 λ . As the antenna height is increased, the number of lobes increases as well.
The difference in the above factors for the case of θ = 0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.
On the other hand, analog television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection in the horizontal polarization off the side of a building is generally less than in the vertical direction. Vertically polarized analog television have been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.
Modeling antennas with line equations [ edit ]
In the first approximation, the current in a thin antenna is distributed
exactly as in a transmission line. — Schelkunoff & Friis (1952)[24] (p 217 (§8.4))
The flow of current in wire antennas is identical to the solution of counter-propagating waves in a transmission line, which can be solved using the telegrapher’s equations. Solutions of currents along antenna elements are more conveniently and accurately obtained by numerical methods, so transmission-line techniques have largely been abandoned for precision modelling, but they continue to be a widely used source of useful, simple approximations that describe well the impedance profiles of antennas.[25](pp 7–10)[24](p 232)
Unlike transmission lines, currents in antennas contribute power to the electromagnetic field, which can be modeled using radiation resistance.[a]
The end of an antenna element corresponds to an unterminated (open) end of a single-conductor transmission line, resulting in a reflected wave identical to the incident wave, with its voltage in phase with the incident wave (thus doubling the net voltage at the end) and its current in the opposite phase (thus net zero current, where there is, after all, no further conductor). The combination of the incident and reflected wave, just as in a transmission line, forms a standing wave with a current node at the conductor’s end, and a voltage node one-quarter wavelength from the end (if the element is at least that long).[25][24]
In a resonant antenna, the feedpoint of the antenna is at one of those voltage nodes. Due to discrepancies from the transmission line model, the voltage one quarter wavelength from the current node is not exactly zero, but it is near a minimum and small compared to the much larger voltage at the conductor’s end. Feeding the antenna at that point thus involves a relatively small voltage but large current (the currents from the two waves add in-phase there), thus a relatively low feedpoint impedance. Feeding the antenna at other points involves a large voltage, thus a large impedance, and usually one that is primarily reactive (low power factor), which is a terrible impedance match to available transmission lines. Therefore it is usually desired for an antenna to operate as a resonant element with each conductor having a length of one quarter wavelength (or other odd multiple of a quarter wavelength).
For instance, a half-wave dipole has two such elements (one connected to each conductor of a balanced transmission line) about one quarter wavelength long. Depending on the conductors’ diameters, a small deviation from this length is adopted in order to reach the point where the antenna current and the (small) feedpoint voltage are exactly in phase. Then the antenna presents a purely resistive impedance, and ideally one close to the characteristic impedance of an available transmission line. However resonant antennas have the disadvantage that they achieve resonance (purely resistive feedpoint impedance) only at a fundamental frequency, and perhaps some of its harmonics. Therefore resonant antennas can only achieve their good performance within a limited bandwidth, depending on the Q at the resonance.
Mutual impedance and interaction between antennas [ edit ]
The electric and magnetic fields emanating from a driven antenna element will generally affect the voltages and currents in nearby antennas, antenna elements, or other conductors. This is particularly true when the affected conductor is a resonant element (multiple of half-wavelengths in length) at about the same frequency, as is the case where the conductors are all part of the same active or passive antenna array. Because the affected conductors are in the near-field, one can not just treat two antennas as transmitting and receiving a signal according to the Friis transmission formula for instance, but must calculate the mutual impedance matrix which takes into account both voltages and currents (interactions through both the electric and magnetic fields). Thus using the mutual impedances calculated for a specific geometry, one can solve for the radiation pattern of a Yagi–Uda antenna or the currents and voltages for each element of a phased array. Such an analysis can also describe in detail reflection of radio waves by a ground plane or by a corner reflector and their effect on the impedance (and radiation pattern) of an antenna in its vicinity.
Often such near-field interactions are undesired and pernicious. Currents in random metal objects near a transmitting antenna will often be in poor conductors, causing loss of RF power in addition to unpredictably altering the characteristics of the antenna. By careful design, it is possible to reduce the electrical interaction between nearby conductors. For instance, the 90 degree angle in between the two dipoles composing the turnstile antenna insures no interaction between these, allowing these to be driven independently (but actually with the same signal in quadrature phases in the turnstile antenna design).
Antenna types [ edit ]
Antennas can be classified by operating principles or by their application. Different authorities placed antennas in narrower or broader categories. Generally these include
These antenna types and others are summarized in greater detail in the overview article, Antenna types, as well as in each of the linked articles in the list above, and in even more detail in articles which those link to.
See also[edit]
^ R′ = G′ = 0 .[25] R′ , at the expense of working with [24] Excepting full-wave loop antennas radiation resistance is typically small (tens of Ohms ) compared to the antenna element’s surge impedance (hundreds of Ohms), and since dry air is a very good insulator, the antenna is often modeled as lossless:The essential loss or gain of voltage due to transmission or reception is usually inserted post-hoc, after the transmission line solutions, although it can be approximately modeled as a small value added to the loss resistance, at the expense of working with complex numbers
References[ edit ]
The dictionary definition of antenna at Wiktionary
How to Wire a Car Stereo to a 12v Battery
Yes, you can connect a car radio directly to a battery. However, you must ensure that the battery you connect it to is a 12 volt battery. It should also preferably be a car battery.
Why can you connect the car radio directly to the battery?
You have to keep in mind that car stereos draw a lot of energy from the battery.
The reason car batteries don’t drain while driving is because the vehicle is constantly charging them.
So although it is possible to connect a car stereo directly to a battery, keep in mind that this will drain the battery very quickly and you will be charging it forever.
How to wire a car radio with a 12v battery
Connecting a 12V battery to a car radio requires some preparation.
In order to properly perform the work, you will need the following tools:
wire strippers
crimp tool
alligator clips
While you could just tie the wires directly to the battery posts, we wouldn’t really recommend that. It is dangerous.
instructions
Follow these steps to connect your car radio to the battery:
1. Strip the wires
You should have three wires coming from your car stereo; black, yellow and red.
Strip about an inch from the end of each of them.
2. Pair the red and yellow wires
These two wires will eventually be connected to the “positive” terminal of your battery.
Twist these wires together. At this point you can connect them directly to the battery connector if you wish. Although it’s really not recommended.
Your best option is to crimp the yellow and red wires onto an alligator clip.
3. Crimp the black wire
The black wire just needs to be crimped onto an alligator clip.
4. Connect to a battery
As previously mentioned, the red and yellow wire combination connects to the terminal marked ‘positive’ on the battery.
The black wires attach to the opposite terminal on the battery.
5. Connect the car radio to the speakers
If your car radio does not have speakers, you will need to connect it to some. Preferably, you should select speakers designed for use in a vehicle. These have low power consumption.
If you use other types of speakers, keep in mind that you may need to power them separately.
6. Turn on the radio
Once everything is connected you can turn on the radio.
Troubleshooting
If you did everything right, it should turn on. If it doesn’t, you probably have one of these issues:
The battery is not charging. To determine if the battery is charged you can use a multimeter, alternatively you can tell by the strength of the headlights. You connected the cables incorrectly – Check out how to properly connect your battery terminals. The radio is not working – This can be due to a variety of factors.
It’s likely that the wiring will be the problem. Even a small amount of charge left in a battery should be enough to power the radio. So check the wiring. If everything is ok, charge the battery. If it still doesn’t work, you have a faulty radio.
Final Thoughts
As long as you have wire strippers, a crimping tool, and alligator clips, you should be able to wire the car stereo directly to a battery with minimal fuss.
If for some reason the radio still shows no power, you should systematically cross out parts, checking that the battery is charged, then checking the connections and finally deciding that the radio is faulty.
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