About CB Antennas
CB Antennas Info Page:
The purpose of this page, is too provide general info about CB Antennas and their operations. Big Hair Antennas are built for higher efficiency and gain than typical CB Antennas made
today.. Big Hair Antennas range from 5' to 50' feet in length, and are made to handle very serious power with the highest efficiency and gain. By special request, we also can offer "silver-
plated" copper coils and Antennas for the highest performance. Click Here to see a Big Hair and IMAX 2000 Antenna Comparision.
Manufactures, Builders, and Examples of High Performance CB Antennas include but are not limited to::
Big Hair CB Antennas
Wilson 2000 Trucker
What is an Antenna?
An antenna is a transducer designed to transmit or receive electromagnetic waves. In other words, Antennas convert electromagnetic waves into electrical currents and vice versa.
Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, radar, and space exploration. Antennas usually work in air or
outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.
Physically, an antenna is an arrangement of conductors that generate a radiating electromagnetic field in response to an applied alternating voltage and the associated alternating
electric current, or can be placed in an electromagnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. Some antenna devices
(parabolic antenna, Horn Antenna) just adapt the free space to another type of antenna.
How CB Antennas Work:
When your transmitter puts a current (Radio Frequency (RF) energy) into an antenna, your antenna responds by producing a magnetic field surrounding the antenna (this is the signal).
When this magnetic wave strikes another antenna (the receiving station antenna), it induces a current on the receiving antenna surface (that current is then converted by the receiving
stations receiver to sound).
The length of the antenna structure plays an important role.
The magnetic field that your antenna puts out will produce an electric current on any metal surface that it strikes, however if the metal that the signal strikes has a length relation to itself
the induced current will be much stronger on the object. We stated before that as a CB signal travels through the air, it completes a cycle in approximately 36 feet. For instance, if the
object that the magnetic wave strikes is 18 feet long (1/2 wave length), 9 feet long (1/4 wavelength) or 36 feet long (1 full wavelength), then the induced current will be much higher than if
the signal struck a metal object that was not some appreciable fraction of the wavelength of the signal. If you have ever heard people say they want to "tune" their antenna, they usually
mean make it have a length relation to frequency they are trying to receive.
This has a special name, it as known as antenna resonance. Every antenna has at least one exact resonance point.
Antenna resonance is the frequency (in MHz) where the antenna is in a state of electrical balance, which is determined by the length of the antenna (every antenna has an exact frequency
it is resonant on). To use some numbers to demonstrate what we are explaining here, let us look at a very simple formula. You can calculate the distance of a wavelength in free space for
any frequency using this formula:
One Wavelength, in feet = 984 / Frequency in Megahertz (MHz)
Lets look at an example:
CB Channel 40 uses the frequency 27.405MHz.
One Wavelength for 27.405, 35.906 Feet = 984 / 27.405
So we want to make a antenna that is resonant on channel 40 and not too large in size. Lets cut a straight piece of aluminum rod to be 1/2 a wavelength long. One Wavelength for 27.405
is 35.906 feet (from the formula above), and we want 1/2 of that, or 17.593. So, we cut our piece of aluminum rod to 17.593 and we have made an antenna that resonates on 27.405 (or
close to that). This piece of rod should pick up (receive) on channel 40 (27.405MHz) well.
OK, now lets look the most basic antenna most CBers are familiar with, the 102" whip, also known as the 1/4 wave whip. Why is it known as the 1/4 wave whip? As we can see if we get
out our calculator, 102 inches is approximately 1/4 of 35.906 feet (1 wavelength). This antenna should also perform well on the CB band because its length relates to that 36 foot
wavelength signal we are trying to receive!
To further simplify things, we have been speaking strictly about receiving - but these same principles apply to transmitting. Our antenna also transmits a strong signal if the antenna we
are transmitting through is resonant on the frequency on which we are transmitting.
This brings us to our next topic - Bandwidth. Most of us use multiple frequencies when we use out radios. So, does this mean our antenna only works good at one frequency, the
resonance frequency? No! Our Antennas actually perform well over a range of frequencies. Most commercial CB Antennas are designed to operate well over the 40 channels (that is a
frequency range from 26.965 - 27.405 MHz). So, if you use your radio on all those frequencies it would be best to make it resonant in the middle around channel 20 or so (27.205 MHz). If
you talk only on a certain channel then set it up for the frequency that you use most. The term that is important here is bandwidth or how much band your antenna works well over. For
example if your antenna works well over the 40 channels then your bandwidth is 27.405 - 26.965, or .44 One method of judging how well (efficiently) your antenna is working is by
To understand SWR or Standing Wave Ratio, we must first understand a few other properties all Antennas have. You may have heard the terms radiation resistance, impedance, input
impedance, feed point impedance. These terms are all referring to the same property of an antenna. When we think of the term resistance we usually think of some type of force that acts
(or impedes). Do not confuse DC resistance with radiation resistance. This is a totally different concept. You can not measure your antenna's impedance by using a Ohm meter on it!
Impedance in antenna terms refers to the ratio of the voltage to current (both are present on an antenna) at any particular place on an antenna. This ratio of voltage to current is different on
different parts of the antenna - which means that the Impedance is different on different spots on the antenna if you could pick any spot and measure it.
In formula terms:
Impedance of antenna = Voltage Field / Current field flowing within antenna.
This is great, but how does this relate to SWR? As you may or may not be aware of, most Antennas are usually designed (and intended) to have an impedance at their feed point of 50
ohms. CB radios that are sold have antenna jacks on them that require they be hooked up to a 50 Ohm load (load - usually your antenna). This is why we use a 50 Ohm line (usually coax
cable) to connect to the antenna. If we have an antenna not properly tuned close to 50 ohms or we used 75 ohm coax instead of 50 ohm coax a mismatch condition occurs. Basic laws of
electronics dictate that if these impedance's (antenna jack, coax and antenna impedance) do not match then maximum power is not transferred. There are all kinds of situations that
could cause a mismatch beside what I gave as an example. Smashed coax, bad connections, incorrect antenna assembly, mis tuned antenna (incorrect antenna length) and objects too
close to antenna are some other common causes.
What happens if there is a mismatch? At this point, lets just say that the antenna isn't tuned right, at the connection of the coax to the antenna, part (or all) of the wave is reflected back
down the line. The amount of the wave reflected back depends how bad the mismatch is. The combination of the original wave traveling down the coax (towards the antenna or opposite
during receive) and the reflecting wave is called a standing wave. The ratio of the two above describe waves is known as the Standing Wave Ratio (aka SWR). Generally you want a low
SWR, preferably less than 2:1. In some mobile installation note that it is not possible to get the ratio lower than this without using a special matching device. This is because the
impedance of most mobile Antennas are lower than 50 ohms. In general, an SWR of 1:5 is fine! This is an area of battle for most antenna experts. Some strive to achieve a 1:1 ratio that
indicates a maximum power transfer through their antenna system.
Physical Demands of CB Antennas
As 27 MHz is a relatively long wavelength for mobile communications, the choice of antenna has a considerable impact on the performance of a CB radio.
One common mobile antenna is a quarter-wave vertical whip. This is roughly nine feet (2.7 metres) tall and mounted low on the vehicle body, and often has a spring and ball mount. A
common misconception is that the '102 inch' whip is the correct length for US CB frequencies; in reality, it is designed to be paired with a six-inch spring, both to bring it to the proper
electrical length, and to enhance its resilience to scraping and striking overhead objects.
Where a nine-foot whip would be impractical, shorter Antennas include loading coils to make the antenna electrically longer than it actually is. The loading coil may be on the bottom,
middle, or top of the antenna, while some Antennas are wound in a continuously loaded helix.
Many truckers use two co-phased Antennas mounted on their mirrors. This arrangement reduces the distortion of the wave propagation due to an unequally-shaped ground plane,
lessening the effect of the truck body on the radiation pattern. In addition, when such an array is properly constructed, it enhances performance to the front and back, while
reducing it to the sides, a desirable pattern for long-haul truckers. However, the efficiency of such an arrangement is only an improvement over a single antenna when the co-phased
Antennas are separated by approximately eight feet or more, restricting this design to use mainly on tractor trailers and some full-size pickups and SUVs. Some operators will only use
one of pair of Antennas; this removes both the complexity and benefit of a true co-phased array, but gives a symmetrical cosmetic appearance that some truck drivers prefer.
Another mobile antenna is the continuously-loaded half-wave antenna. These do not necessarily require a ground plane to present a near 50 Ohm load to the radio, and are often used
on fiberglass vehicles such as snowmobiles or boats. They are also ideal for base station usage where the circumstances preclude the use of an antenna that requires a ground plane
to function properly.
Handheld CBs often use either a telescoping center-loaded whip, or a continuously-loaded “rubber ducky” antenna.
Base CB Antennas may be vertical for omnidirectional coverage, or directional "beam" Antennas may be used to direct communications to a particular region. "Ground Plane" kits exist as
a mounting base for typical mobile whips, and have several wire terminals or hardwired ground radials attached. These kits are designed to have a mobile whip screwed on top (again,
the full-length steel whip is a preferred candidate) and mounted on top of a mast. The ground radials take the place of the vehicle body, which is used as a counterpoise for the mobile
whip in a typical vehicle installation.
Choosing a CB antenna is fairly easy once you have sorted through a few basic rules. This information should help.
- Top loaded (helical wire-wounds) perform better than center loaded Antennas, center loaded Antennas perform better than base loaded Antennas.
- Taller Antennas perform better than shorter ones.
- Antennas mounted higher perform better than if mounted lower.
- Single Antennas perform better when mounted as close to center as possible on metal vehicles.
- Base loaded Antennas cannot be co-phased with satisfactory results.
- Fiberglass and aluminum vehicles, or those with little available ground plane, need co-phased or "no ground plane" Antennas systems.
- The physical length of the antenna should be determined by the likelihood of repetitive hitting of overhead objects and/or the type and strength of the antenna mount itself.
- At least two-thirds of the antenna should be above a vehicles roof line for optimum performance.
- If the antenna/mount combination is available in a kit form, you will normally save money by purchasing it as a kit.
- The bandwidth of the antenna should always meet or exceed the needs of a 40 channel CB.
- If you put 4 watts into a four-foot antenna, you will get the same power out of that antenna as if you were putting 2 watts into a 102-inch whip.
- If you put 4 watts into a 3-foot antenna you will get the same power out as if you were putting about 1.5 watts into a 102-inch whip.
- If you put 4 watts into a 7.5 inch antenna on a hand held CB, it would put out as much power as a third of a watt into a 102-whip.
- If you put 4 watts into a 102-inch whip antenna, it is the same output as if you put 11 watts into a 3-foot whip.
- If you put 4 watts into a 102-inch whip antenna,, it is the same as if you put 14 watts into a 28-inch antenna.
- If you put 4 watts into a 102-inch whip antenna, it is the same as if you put 54 watts into a 7.5 antenna.
- If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be "LONG" and reduction of physical height and/or conductor length will correct this
Citizens Band Frequencies and CB Antenna Requirements
Citizens Band frequencies are at the top end of the high-frequency band, or stated another way, just below the bottom end of the VHF band. Here is where base-loaded CB Antennas
usually work well. A mobile antenna should be placed in the middle of the vehicle roof to make best use of the ground plane. The longer the CB whip, the better the performance. The
more you load an antenna, the shorter it gets, and the lower the radiation resistance. Lower radiation resistance means less signal output and input. Select the
Phased Two CB Antenna System
You might also consider a phased two CB antenna system to give an additional 3dB of gain. You can purchase "co-phase" coaxial cable assemblies, or make your own using a coaxial
cable T-connector and two equal lengths of RG8AU coax. Make sure that each side of your co-phased coaxial cable feed lines are identical in length, down to a fraction of an inch, but be
sure to avoid a precise half-wavelength on 11 meters for your phasing harness. Mount the Antennas on either side of your vehicle. The best performance will be to the front and rear of the
vehicle, with slight nulls to each side of the vehicle.
The easiest way to get the strongest signal out on Citizens Band is to use an unloaded whip CB antenna. You may purchase these stainless steel or fiberglass whips at any CB Radio
store. Mount the whip as high on your vehicle as possible. Because it has no loading coils, it will offer unity gain without loss whereas you might expect a loss of 1 to 2dB from a loaded
How does a CB radio antenna work on 27MHZ?
A citizens band (CB) radio antenna is a device designed to do two things: It captures radio-frequency signals that are then converted to electrical signals by the receiver, and it takes
electrical signals from the transmitter and converts them into radio-frequency signals. This second function is where tuning comes into play, because an antenna has to radiate radio-
frequency signals, something that's done best when the length of the antenna precisely matches the wavelength of the transmitted radio frequency.
You can determine the proper length of an antenna by using a formula:
Wavelength (in feet) = 984 / frequency (in megahertz)
The CB portion of the spectrum begins at 25.01 megahertz, so a full wavelength antenna would be a bit more than 39.34 feet long. That's obviously a little long to attach to your bumper, so
people tend to use CB Antennas that are a fraction of the wavelength: 1/2, 5/8, 1/4 and 1/8 are all common wavelengths for Antennas. In the case of CB, the 1/4 antenna at just under 10
feet long is the common "whip" that you may see on cars and trucks.
The trouble is that there are 40 channels on modern CB transceivers, each corresponding to a different frequency. It's not practical to have a separate antenna for each frequency, so
antenna designers have to compromise, usually picking a frequency in the middle of the spread and choosing the antenna length to correspond.
When a compromise like this is made, you have to see whether it's a good compromise. This is done by measuring the Standing Wave Ratio (SWR) of the antenna and cable between
the antenna and tuning the antenna until the SWR is acceptable.
Every antenna and every antenna feed-line have a characteristic impedance, or opposition to electrical current. In an ideal situation, the impedances of line and antenna match perfectly,
and 100 percent of the electrical energy sent to the antenna is converted to radio energy and radiated into the atmosphere. In a less than ideal case, when the impedances aren't perfectly
matched, some of the electrical energy sent to the antenna won't be converted to radio energy, but will be reflected back down the feed-line. The energy reflecting back from the antenna
causes standing waves of electrical energy in the feed-line. (An example of standing waves outside the electronics world is found in river rapids. When water passes around and between
boulders it may form a wave that doesn't go up or down the river, it just stays in one place. That is a standing wave of water.) The ratio of highest voltage on the line to lowest is the
standing wave ratio. In the perfectly matched system, the SWR is 1:1.
To tune an antenna, use an SWR meter attached between the transmitter and antenna feed-line. Depending on the meter, you can either use a button on the meter to generate a signal
on the various channels, or key the microphone on the CB transceiver to generate a signal while you look at the SWR reading. In general, if the SWR never goes above 1.5:1, you're in
good shape. If the SWR does go above 1.5:1, then watch the meter on different frequencies to see the trend develop: The SWR will be greater either on the higher channels or the lower. If
the SWR is greater on the lower channels, then try gradually lengthening the antenna by moving it in the base. If the SWR is greater on the higher channels, try shortening the antenna.
Do be aware that the electrical ground of the antenna, the structure around the antenna and any other Antennas near the CB antenna can all affect the antenna's impedance and the SWR.
There are enough variables that tuning an antenna blends art and science, but your equipment and radio contacts will all be grateful if you take the time to tune up.
Click Here for an IMAX 2000 Antenna Comparison
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Other CB Radio Sites I Recommend You Should Check Out:
The CB Radio Club - Probably the best CB Radio Community site on the net, a whole host of features are there such
as a great forum, CB radio groups you can join or start, Reviews on equipment, Free Classifieds, shack slideshows,
watergates, and mods. My top pick!
Here is a direct link to their CB Radios For Sale and Classifieds section as well and their CB Radio Forum page is
also something you may want to check out.