CB Antenna Tuning

    1. Why tune your antenna?
    2. What is SWR?
    3. How to tune your antenna.
    4. Test the power output.

NOTE:  This section assumes you are using the same type meter and are adjusting  or testing with a normal low power CB radio system.  If you are testing a different type radio or are using a different type meter, this will only serve as a guide and you must adjust the steps according to the equipment you are using.

The Meat of it all!!

1. Tuning advantages:
It can give more range to the channel area you use. Most antennas are somewhat pre-tuned but since every radio is different the antenna should be tuned to the radio, the area it is mounted and the length of the cable also play a part in the tuning. In theory, if an antenna was far enough out of tune, it would burn up the radio but I have never seen one close to that bad except when a guy broke his firestick and he tried to keep using it!! Tuning will also give you a cleaner signal.

2. SWR In very basic terms.
Your radio puts a signal out in a wave pattern that travels down the cable and up the antenna to the load, if the antenna was PERFECTLY tuned (impossible), the entire signal would broadcast from the antenna due to the load on the antenna and many other factors that we won't go into.
Since the antenna can not be perfectly tuned across the radio band, when you transmit and the wave travels to the antenna load, most of it is broadcast but a portion is reflected back to the radio. The SWR (Standing Wave Ratio) is the ratio of the amount of signal transmitted vs. the amount NOT reflected. Anything reflected back will reduce the power where it interacts and causes the voltage of the signal to be lower than the output voltage of the radio, the meter reads the output voltage and the lower voltage on the line if any is caused by the reflection.
A 1:1 ratio would mean that there was no lower voltage and hence no reflection, a 3:1 (very bad) would mean that 25% of the signal was being reflected back and dropping the effective power of the radio to 75%. A 1.5:1 is generally about the highest ratio that you should see if all is working properly. The better the broadcast of the antenna, the cleaner your signal will be and the farther it is capable of traveling depending on weather conditions.
Normally you set your SWR at the channel that you use most commonly to get as close to a 1:1 as possible and then check it at other channels to make sure it is not too far off tune. If you can not get it to tune properly, you can check some of the following:
Loose connection
Dirty connection
Cut cable
Kinked cable (cable should go around bends smoothly and should never be folded back on itself to tightly to cause kinks)
Antenna Ground
Antenna loose
Antenna damaged
Ground plane of the vehicle (vehicles metal surface area the antenna uses for impedance matching, too much to explain here and Firesticks do not need it [as much], that is why most wheelers use them on Jeeps) (Note: on Firesticks, the smooth area toward the top where the spirals end must be above the roof line to work correctly)
Other things can cause trouble but these are the most common.

3. The how-to’s of tuning:

First you need a meter, some high end CB radios have one built in but for most applications, you will need to purchase or borrow one. I use one from Radio Shack that runs about $36,Model: 21-534.




Along with this unit, you also need an adapter cable to attach this unit to the CB. Again, I use a Radio Shack 2’ RG-58 Coax Cable that runs about $6.50, Model: 278-968.

A. To start, the CB must be fully installed and operational. Make sure the CB radio is turned off when hooking and unhooking connectors. Disconnect the antenna cable connector from the back of the CB radio and connect it to the back panel connector of the meter that is marked for the antenna. Next, connect one end connector of the 2’ RGB coax cable to the back panel connector of the meter that is marked for the CB radio or transmitter, connect the other end of this cable to the antenna connection on the rear of the CB radio.

B.  On the front panel of the meter, set the range switch to the mid setting (200W), set the Function switch to CAL.




C.  Turn the CB radio on and set to the desired channel. Hold down the Mic Button but do not speak or use with loud noises present, adjust the Calibration knob till the meter needle points to CAL.




D.  Release the Mic Button and set the Function switch to SWR.




Press the Mic Button again and read the SWR on the appropriate scale on the meter. For standard CB radios this will be the lower scale on the meter. Repeat this check using several channels on the radio. The actual adjustment of the antenna varies by antenna type. Firesticks have a rubber tip at the top and there is a knurled knob and lock knob adjustment under the tip that you have to adjust and lock. Base loaded, steel whip antennas, usually have a set screw in the base that holds the steel whip in place, normally you loosen this set screw and adjust the steep whip up or down and retighten the set screw. Check with the manufacturer of your antenna if you can not determine the adjustment location. SWR reading at 1.0 is the optimal but is usually not realistic, the radio will vary at different channels. Try to adjust the radio so it will work on all channels and be the closest to optimum at the channel you will use most. This chart gives you and idea of the SWR readings.




The percentage of signal loss is greatly affected as the ratio goes up. At an SWR of 1.0 there is no loss, at 1.1 there is only 0.22%, at 1.2 it is 0.8 and at 1.5 it climbs to 4%. That still means that at and SWR of 1.5, 96% of the signal is still going out, but and 2.0 the loss is 11.1%, at 2.5 it is 18.4% and when you hit 3.0 it climbs to 25%.

4. Testing power output:
A. To start, the CB must be fully installed and operational. Make sure the CB radio is turned off when hooking and unhooking connectors. Disconnect the antenna cable connector from the back of the CB radio and connect it to the back panel connector of the meter that is marked for the antenna. Next, connect one end connector of the 2’ RGB coax cable to the back panel connector of the meter that is marked for the CB radio or transmitter, connect the other end of this cable to the antenna connection on the rear of the CB radio.

B.  On the front panel of the meter, set the range switch to the low setting (20W) for a CB Radio as the average power is around 4 Watts, set the Function switch to POWER.  Set the mode switch to PEP.  If you are testing a higher power unit or different type radio, the setting may be different!




C.  Select the channel on the CB radio you wish to test.  Hold down the mic button but do not talk, read the power level on the low power scale (lower scale marked with an L on the right side).