CB Antenna Basics » W0IS.com

A good antenna for CB communications need not be elaborate or expensive. In general, there are two important considerations to keep in mind.

First of all, antenna height is the most important factor! A poor antenna at a high location will almost always outperform a good antenna at a low location. This is because communications at CB frequencies is generally "line of sight". Radio waves have some ability to penetrate objects, but this is limited. In general, they behave the same as light. Two radios will be able to communicate if you would be able to see one antenna if your eyes were at the same location as the other antenna. Because radio waves have some ability to penetrate objects, the actual range is somewhat longer. (10% is a good rule of thumb.) But in general, if an antenna is located in a spot where it can't "see" the antenna at the other end, then the two radios won't be able to communicate. And in general, if they are located where they can "see" each other, then they probably will be able to communicate.

Since you can see further when you are at a high location, it stands to reason that an antenna will "get out" further if it is at a high location.

This factor cannot be over-emphasized. A poor antenna at a high location will outperform a good antenna at a low location.

Of course, it is best to have an antenna that is both high and good. But if you have to chose, take the poor antenna at a high location.

In the United States, FCC rules govern the height of CB antennas. The antenna is legal if it complies with EITHER of the following rules:

1. It is no more than 60 feet above the ground, OR
2. It is no more than 20 feet above the top of the tree or building to which it is mounted.

The other factor to keep in mind is that, in general, a larger antenna will work better than a smaller antenna. This rule does have a limit: In general, a CB antenna should be "full sized". This means that it should be 8-1/2 feet long, which is a quarter of the radio wave's wavelength. Some specialized antennas might be longer than this, but in general, nothing is gained by simply making the antenna bigger past this point. In fact, simply making an antenna larger will probably inhibit its performance. For a home base station antenna, it is usually easiest just to make the antenna full sized.

For a vehicle, however, an 8-1/2 foot antenna, while possible, might not be convenient. Therefore, most mobile antennas are shorter than this, and the manufacturer uses various "tricks" (ordinarilly, adding a coil of wire at some point) to shorten the antenna. These tricks always come at a price, however, and that price is that the antenna won't work as well as if it were full size. Therefore, as a general rule, a longer antenna will work better than a shorter antenna. For example, all other things being equal, a four-foot antenna will work better than an 18 inch antenna.

In general, when installing a CB antenna, you have to think about the following factors, and we'll discuss:

1. You will need the antenna itself.
2. You will need some way to mount the antenna.
3. You will need to connect the antenna to your radio, usually with a coaxial cable.
4. You will need to decide on the orientation (vertical or horizontal).
5. You might need to adjust the antenna so that it is properly tuned.

Since these factors present different problems depending on whether you will have a fixed station ("base station") or one in a vehicle ("mobile"), we'll discuss those separately.

Base Station Antennas

An antenna for a CB base station can be remarkably simple, especially if you remember that the height of the antenna is a much more important factor than the antenna itself. The most simple type of antenna is the dipole, which is very easy to construct yourself.

A dipole is nothing more than two pieces of wire, each of which is 8 feet 6 inches (102") long. Virtually any type of wire will work. The size of the wire makes very little difference. The wire can be either insulated or uninsulated. (Of course, you will need to remove the insulation at the point where you make the electrical connections.) Copper or copper-clad wire is best, but as a practical matter, the composition of the wire makes very little difference, as long as it conducts electricity. So, for example, steel wire will generally work just fine. The main consideration in deciding on what wire to use is mechanical--you generally want to use something that won't fall down. Another consideration might be stealth--you might want an antenna that is not visible. In that case, you can use extremely thin wire. For an emergency antenna, you can use any available wire. The possibilities are limitless, and the differences in performance will be so small as to be unnoticeable.

Here is a diagram of how to construct a dipole antenna. The mechanical details are not critical. The easiest method is to use ropes at either end, and tie them to convenient (and high) supports, such as trees or buildings. It is best to install the antenna as much in the clear as possible. It is not always possible to have it completely in theclear, but keep it as far away as possible from other objects, particularly anything metallic. Sometimes, it might even happen that the antenna is touching other objects. As long as those other objects are non-conductive (non-metallic) and generally dry, this is not always a major problem. Again, height is almost always the most important factor. So if you have a choice of putting an antenna high in a tree where it touches a couple of branches, that's probably a better choice than lower in the tree where it is completely in the clear. (If the antenna is touching branches, you might notice that it doesn't perform as well when the tree is wet, but this effect is generally very minor.)

The antenna does not have to be perfectly in a straight line. It's common to have it in an "inverted vee" formation, with the center of the antenna higher than the two ends. There's really no reason why it couldn't be a "vee", with the ends higher than the middle. In fact, if necessary, it's possible to have the wires "zig-zag" a certain amount without much difference in performance.

If one end of the antenna is higher than the other end, then it's best to have the center of the coaxial cable connected to the higher side, and the outer braid of the coax connected to the lower side.

You will have to decide whether the antenna will be vertical or horizontal. The exact orientation is not critical. In fact, even if it runs at a 45 degree angle, the difference will be barely noticeable. (In fact, if it's at a 45 degree angle, it will function as both a vertical and horizontal antenna.) This is important because the two antennas involved in the communication (yours and that of the person you are talking to) should be oriented the same way--either both of them should be vertical, or both of them should be horizontal. If one of them is vertical and the other one is horizontal, there will be a fairly significant decline in performance.

Most CB antennas are vertical. This is because CB's are most commonly used to communicate with mobile units, and in a vehicle, it's much more convenient to use a vertical antenna. So if you want to communicate with existing CB's, or with CB's in a vehicle, then it's best to orient your antenna vertically--running up and down. However, if you want to set up communications between two locations, it doesn't matter whether the antennas are vertical or horizontal--as long as they both have the same orientation.

In fact, for communicating between two locations, there might be an advantage of using horizontal antennas. Because most other CB's use vertical antennas, using a horizontal antenna might reduce interference from other stations.

A dipole antenna is slightly directional. It transmits and receives better broadside to the antenna, and does not work as well off the ends. For example, if you have a dipole running north to south, it will get out slightly better to the east and west. This is not a major effect, but it is noticeable. Therefore, if you are setting up communications between two locations, it would be best to have the antennas parallel to one another. For example, if one location was due north of the other, then it would be best to have both antennas hanging east to west.

When constructing an antenna, it is important to have good electrical connections. On a dipole, this means that you will need a good connection between the two wires inside the coax and the antenna itself. For a temporary antenna, simply twisting the wires together will actually work quite well. However, for a permanent antenna, it is better to make a more permanent connection. The simplest way is to solder the connections, and this will ensure a long-lasting connection that is both electrically and mechanically solid. Soldering irons are very inexpensive (usually less than five dollars for a perfectly adequate model). They are available at Radio Shack, hardware stores, and home improvement stores. Often, they come with a small amount of solder, usually more than enough for many small jobs. Here is one inexpensive soldering iron available online for only a couple of dollars:

When buying solder for any kind of electrical work, you should always buy "rosin core" solder. It's available at Radio Shack or hardware stores:

If you don't want to solder, similarly good results can be obtained by some sort of compression fitting to splice the wires together. The simplest way to do this is to use a nut, bolt, and two washers. After twisting the wires together, place them between the two washers, and tighten with the nut and bolt. (Use stainless steel hardware to prevent corrosion which can be caused by dissimilar metals.)

Anther convenient option is the "split bolt" connector. As the name implies, this is a bolt, made of either copper or steel, which is split down the middle. You simply place the wires inside of the split, and then tighten the nut to compress the wires together. These connectors come in various sizes, and should be available at hardware stores:

(The split bolt shown above is for larger wires, and is much too large for use on antenna wires. It's included because it has the best photo. These will be available at hardware stores in various sizes, or can be ordered online by following the links to smaller connectors on that page.)

If you are using a cable with connectors already attached, it can be convenient to use a coaxial socket, and simply connect the existing cable to this socket. The cable connectors used on CB-type cable are called "PL-259" connectors, and the socket is called an "SO-239" connector. Here is an SO-239 connector, which could be used to form the center of the antenna. (The price shown on the picture below is for a 10-pack):

Since a diple antenna is so easy to make, I'm hesitant to recommend simply buying one. However, if you wish, you can simply buy one pre-made:

As noted above, the dipole antenna can be used in the vertical position, and will work quite well. If does have a couple of disadvantages, however, if used vertically. First of all, it might be inconvenient to have the coax cable coming out away from the antenna. It would make for a more convenient and neater installation to have the cable attached at the bottom of the antenna. Also, if the cable needs to run close to the antenna itself as it goes down to the ground, and not directly away from the antenna, this might adversely affect how well the antenna radiates. The effect is not large, but it might be noticeable.

For these reasons, for a vertical antenna, it might be more convenient to use a "ground plane" antenna. This is a close relative of the dipole antenna. The center conductor of the coax is connected to a single piece of wire (or other metallic object, such as an aluminum tube) which is 8 1/2 feet long. This conductor goes straight up vertically from the coax. The outer braid of the coax, instead of being connected to a single wire, it is connected to multiple wires or conductors. Each of these conductors is also 8 1/2 feet long, and extends outward horizontally from the point where the coax attaches. They extend out radially, so they are sometimes called "radials".

It is most common to use three (or sometimes four) radials. In theory, the antenna is more efficient if more radials are used. But after three or four, the difference in performance is negligible, so there's really no need to add more radials.

The radials should be spaced more or less equally around the base, extending in all directions. The exact placement is not critical, however. So if one of the radials is a little bit off center, this won't affect the performance of the antenna.

Here is a diagram of a ground plane antenna:

This antenna can be constructed with wire, and supported by ropes. It could even be constructed of a non-metallic material, such as wood or PVC, with the wires attached to that support structure.

It's most common for this type of antenna to be made out of aluminum tubing. It would certainly be possible to make your own ground plane antenna using aluminum tubing, simply by following the instructions below, and if you have some tubing available and some rudimentary construction skills, it wouldn't be difficult to make your own.

However, if you don't already have the materials, this is one of those cases where buying the finished product probably costs less than buying the raw materials yourself. They are available at Radio Shack, and other places (such as truck stops) where CB products are sold.

Some base antennas will work slightly better than others. With a ground plane antenna like the one shown above, most of the signal radiates outward. However, a portion of the signal will go straight up, where it doesn't do any good. Some antennas provide "gain" by limiting the amount of energy going straight up, and maximizing the amount of signal going straight out.

Please support this page by supporting our advertisers by using the following links:

The difference between a ground plane and a "gain" antenna is not great, but it might be enough to make the difference in some cases. Therefore, if you are going to purchase an antenna, you might consider paying a bit more for a "gain" antenna.

In addition, some of these antennas do not require the radials, so they do make for a somewhat more compact intsallation. For example, the following antenna is 24 feet long, but does not require ground radials. It will get out somewhat better than a ground plane antenna or dipole:

If you go with a manufactured base antenna, you will need a method of mounting it. All of these antennas clamp on to a vertical mast. In general, these masts have a 1-14" outside diamter, although most antennas will fit on a mast of slightly different diameter. So a homemade mast made of other convenient materials, such as pipe, are possible.

Masts generally come in either five foot or ten foot sections, and the ends are tapered so that sections can be added (within reason, so that the structure still supports itself). Here is one example of what is available:

Because CB antennas use the same masts and mounting hardware as TV antennas, these items are readily available at Radio Shack, hardware stores, and home improvement stores. The question of the best way to mount an antenna is usually best solved simply by going to such a store and looking at the available hardware to see what best fits your application. The most common methods are the following:

For mounting on top of a roof, either a flat roof or with a peak, a tripod is often most convenient:

A bracket of this type can be used to mount the mast on the side of the house:

There are mounts available to mount the mast to an existing chimney or vent pipe. (Particularly in the case of vent pipes, you need to make sure that the pipe will support the added load.) Here is an example of a chimney mount held in place with steel straps:

Many other mounts are available, and these examples are given just to give some ideas.

When installing an antenna, some words should be said about safety. Every year, people are killed putting up antennas. This happens two ways. First of all, the fall off their roof or while climbing. So basic safety procedures should be followed. Go on the assumption that you will stumble, and make sure that if you fall, you will be stopped before you hit the ground.

The other class of deaths comes from electrocution. If the antenna touches a power line, either when you are putting it up, or when using it, then you will probably die! Sometimes, even with the best installations, antennas fall down. Therefore, make sure that when it falls down, it won't hit a power line. Don't go on the assumption that it won't fall down. Go on the assumption that it will fall down, either when you're installing it or when you're using it, and make sure that there's no possible way it can touch a power line when this happens.

Whatever type of antenna you use, you will need coaxial cable to connect it to your radio. For a CB radio, you should use "50 ohm" cable. (This is not the resistance of the wire, so it cannot be measured with an ohmmeter.) The most convenient method is to buy the cable by the foot. It is most commonly sold as "RG-58" or "RG-8" cable, sometimes with another letter after the number. Cable of all different quality and price is available, but for reasonable lengths (such as 50 feet), there is really very little difference. If you buy the cable by the foot, you will need to buy the PL-259 connectors to attach to your radio (and the antenna, if it has this connector). Cable is available by the foot at Radio Shack, and at many truck stops. I prefer the connector which you solder directly to the cable:

For this type of connector, you will also need a reducer to fit the smaller RG-58 cable:

Directions for soldering a PL-259 connector can be found many places on the internet, including the following site:

How to solder a PL-259

Soldering a connector, while not particularly difficult, does take a little bit of time and practice. Soldered connectors are better, but if you are absolutely convinced that you can't solder, there are crimp-on connectors available:

You can buy coaxial cable in various lengths with the connectors already installed. This is convenient, in that you don't need to install the connectors. But you are also stuck with the length that the manufacturer supplies, which may or may not be the length that you need. Also, it makes it more difficult to route the cable. If you put on your own connectors, then you can route the cable through a small hole, and then add the connectors. If you go with the connectors pre-installed, then you can't go through holes that are smaller than the connector.

But cable with pre-installed connectors are easier to find, since most truck stops will have various lengths in stock, but they might not sell it by the foot. For example, here is a pre-made cable which is 18 feet long:

Other typical lengths are 25, 250, and 100 feet. If you need to add two cables together, you will need a "barrel" connector such as this:

As noted above, the type of coax used for CB radios is "50 ohm" coax. The type of coax used for TV antennas is "72 ohm" coax. If you are buying coax, then you may as well buy the right kind, if it's available. However, the TV coax is much easier to find. It's sold at almost every hardware store and home improvement store, often at a lower price than 50 ohm CB coax. In theory, TV coax should not be used for CB applications, because it is the wrong "impedance". However, as a practical matter, it makes very little difference. So if you need to install a CB antenna, and only TV coax is available, it will work, and you really won't notice the difference.

There is a practical problem, however, and that is that the TV coax is much harder to work with, because it typically has a solid aluminum outer shield, rather than braided copper wire. Aluminum is much harder to work with. In particular, it's practically impossible to solder to it. With a little bit of creativity, you can make a PL-259 connector to fit on this cable, but it probably won't be a very long-lasting connection. So for a short-term temporary solution, you can simply do your best to make the connection.

The connectors that come with TV cable are called "F connectors", and they are put on with a special crimping tool. If you have a piece of TV cable that you want to use, the easiest way is to use an adapter which converts the F connector to a PL-259. These adapters are available at Radio Shack, and online:

Using TV cable for a CB antenna isn't really an ideal thing to do, but it will actually work just fine in most cases, sodon't hesitate to use it if necessary.

Mobile Antennas

A mobile antenna on a car presents unique problems. In most cases, it is difficult to install a full-size 8-1/2 foot antenna, so a compromise is generally necessary. Also, the antenna needs to be mounted in such a way that it will not come off at high speeds, or during an accident. Finally, height is still important, so the higher on the vehicle you can mount the antenna, the better.

As with a base antenna, there are three major elements: You need an antenna, you need some way to mount it to the vehicle, and you need a cable to go to the radio. In many cases, you can buy all three parts in one package. In some cases, you will buy the three part separately. Most of the examples shown below include everything you need for one price.

The easiest method for a temporary installation is to use a magnetic antenna. The antenna has a strong magnet which holds the antenna to the vehicle. One advantage of a magnetic antenna is that you can move it easily. You might not want to have the antenna mounted on top of the roof all of the time, but that is the best spot for it, because of the additional height.

Therefore, a magnetic antenna could be installed on the trunk, but if you need extra range, you could move it to the top of the car. Here is one inexpensive magnetic antenna:

This type of antenna mount is designed for a mirror or luggage rack:

This type of antenna mounts to the lip of a car's trunk. This mount, or ones similar to it, might also fit the rear door of a van or hatchback:

(Note, the trunk-mount example shown above includes only the mount and coax, and not the antenna itself. If you buy separate parts, make sure that the antenna fits the mount, since there are at least three types of threads available.)

All of the links shown above are just examples of what is available. Unless you go with something simple like a magnetic mount, it's usually worth the time to go to a truck stop and simply browse what is avaialble that would be best for your particular circumstances.

Tuning your antenna

An antenna needs to be tuned to a particular frequency. For example, the antennas shown above are 8-1/2 feet long, because 8-1/2 feet is a quarter wavelength on CB frequencies. Generally, that length will be very accurate, and the antenna will work well with no further tuning. However, the physical location of the antenna can affect how well it is tuned, and it is often desirable to do some "fine tuning" to make sure the antenna is tuned to the right frequency.

To make sure that the antenna is properly tuned, you will need some kind of test equipment, and the most inexpensive piece of equipment is the "SWR meter". Some CB radios will have a built-in SWR meter. The built-in meters generally are not extremely accurate, but extreme accuracy is not necessary. Therefore, if you have a built-in meter, you can just us that, and nothing else is necessary.

If you do not have a built-in meter, you may want to acquire one. However, it is not absolutely necessary to have one. If you follow the directions to build an antenna, or follow the manufacturer's instructions for a suggested starting point, you will probably be close enough so that no further tuning is necessary. Therefore, I would consider the SWR meter to be a useful optional accessory, and not an absolute necessity. They are, however, very inexpensive, so purchasing one is a good idea.

A high-quality SWR meter is not necessary. The cheapest available ones will work just fine for everything you need it for. The cheapest one I have been able to find is this one, which is inexpensive, and is perfectly adequate:

To use the meter, you will need a short piece of coax with PL-259 connectors on each end. If you don't have one, then you might want to pay a few dollars extra and buy an SWR meter that comes with a short cable:

Using the SWR meter to test your antenna is quite simple. There are two connectors on the meter. One goes to your radio, and the other one goes to your antenna. Make sure you hook them up in the correct direction. (From the unhappy customer's review on the Amazon page above, it sounds like he had it hooked up backwards.)

You will want to check your SWR on three different channels--on channel 1, channel 20, and channel 40. So you repeat this procedure for each channel, and write down the results.

Put the switch on the meter on "Forward" ("FWD"). Then, key the microphone on your radio. While you hold down the microphone button, adjust the knob on the front of the meter, until the meter moves all the way to the end of the scale, to the spot where it is marked "SET" or "CAL" (for calibrate). Then, change the switch to "Reflected" ("REF") and hold down the mike button again. If your antenna is absolutely perfect, then the meter will not move at all, and it will be pointing to "1". (This is a ratio, so the "1" really means "1:1", which you would read as "one to one".)

In practice, the meter will probably move a little bit.

Repeat this whole procedure for those three channels, and then compare the results.

If all of the readings are below 3:1 (in other words, they're not in the red), then you really don't need to do anything else. However, if it's that close to the red, it's probably worth doing some tuning.

A perfect situation would be no needle movement (1:1 SWR) on channel 20, with slightly higher values (meter moves a little bit) on channels 1 and 40. If that's what happened, then you are done, and your antenna is perfect.

If the SWR is too high, then you will want to tune the antenna. You do this by making the antenna either longer or shorter. On a manufactured antenna, there will be a set screw which loosens part of the antenna so that you can move it in or out. For a wire antenna that you built yourself, then you will either remove wire or add more wire (an inch or so at a time).

You can tell whether you need to lengthen or shorten by comparing the SWR readings you obtained for channels 1 and 40:

If you have a lower SWR on channel 1, and a higher SWR on channel 40, this means that the antenna is a little bit too long, and you need to shorten it.

If you have a higher SWR on channel 1, and a lower SWR on channel 40, this means that the antenna is a little bit too short, and you need to make it longer.

You simply adjust the length, make the three SWR readings again, and then adjust again as necessary.

If you are working with a short mobile antenna, then you will need to make very small adjustments, such as a quarter inch or even an eighth of an inch at a time. If you have a full-size antenna, then you can make adjustments of about an inch at a time.

The SWR will change when you move the antenna, so when you do these adjustments, the antenna should be as close as possible to its final location. Also, when making these measurements, take care to keep metal objects away from the antenna, since they will affect the reading.

There is a certain amount of satisfaction that can be derived from having an antenna that is perfectly tuned. However, as a practical matter, as long as the SWR is less than 2:1, it won't get out any better from further adjustments. In fact, in most cases, an SWR of 3:1 or even a bit higher won't do any harm.

Conclusion

This discussion has covered the basics, and for the vast majority of installations, should allow you to install a very good antenna. If you want more information, a number of very good books were published in the 1970's. The physics hasn't changed over the years, but most of these books are no longer in print. Fortunately, most of them are still available used from Amazon, eBay, and other sources. Here is a selection of some of the available books:

Return to my main page
Return to the Emergency Communications page
Copyright and Privacy Notice