How to Tune A CB Radio

Have you ever struggled to get the best out of your CB radio? Are you frustrated because you bought a CB radio to stay in contact with your friends, but you can barely hear each other from one end of the street to the other? Are you worried you might damage your radio if you amp it up? 

If you set up your CB equipment correctly, you can get great quality sound, range and experience without damaging the gear, and it all starts with setting up your CB antenna system properly. 

Getting this right means optimum performance from your whole CB radio, and you reduce the risk of damaging your equipment. So, how do you tune a CB antenna to get the best out of your CB radio? 

First, you have to mount your CB antenna correctly. This usually means ensuring it is correctly grounded and you have a decent ground plane. Make sure your CB radio has been installed and connected according to the manufacturer’s instructions. 

Next, use a Standing Wave Ratio (SWR) meter to tune your CB radio antenna. By checking the SWR readings on channels 1 and 40, you will find out how well tuned your antenna is. 

Your aim is to have an SWR reading as close to 1:1 as possible and certainly no higher than 1:2. If the SWR reading is higher on channel 1 than channel 40, your antenna is too short. 

If the reading is higher on channel 40 than channel 1, the antenna is too long. Make tiny adjustments to the antenna length until the SWR reading is about the same on both channels.

When tuning a CB radio, it is important to understand that the antenna is being tuned, not the radio. Approved CB radios are subject to FCC regulations and cannot be modified. Correctly mounting and tuning your antenna will ensure you get the best out of your CB radio without damaging it or breaking the FCC regulations.

What Should You Expect from Your Cb Radio Equipment?

Source

CB radio gear normally comprises of:

  • Radio set (sometimes they come with an inbuilt SWR meter)
  • Microphone 
  • CB antenna 
  • CB antenna mount and washers (normally come together as a kit)
  • Coaxial cable 
  • Grounding cable
  • Bracket (you may have to source this separately) to attach the antenna system to your vehicle
  • Other nuts and bolts to connect it all together 

In addition, you’ll require the appropriate tool kit for making adjustments and an SWR meter for tuning your antenna. 

Out of all this equipment, the antenna will determine how well you can hear and more importantly, how well you transmit. 

If your CB radio and antenna system is not set up properly, you may get sub-optimal transmission and/or reception, damage your radio, or break the FCC regulations around use of your CB radio.

How Do I Know If My Cb Radio Is Working at Its Best? 

To start with, you can tell your CB radio is working well just by the quality of your communications. 

Receiving messages is possible with fairly basic antennas. You can normally get some radio reception with a wide variety of objects, including coat hangers! The real test is in the quality of your transmissions. 

If your friend can’t hear your messages, either you haven’t set up your equipment well, or they haven’t. If you can’t hear each other, it is best for both of you to check your equipment as just one of you with sub-optimal set up can impact the communications between both of you, regardless of how well the other person has set up their CB radio. 

Ideally your antenna is mounted centrally and high as is practical on your vehicle to give you the best ground plane and to minimize unnecessary interference. 

The antenna mount and coaxial cable should be grounded by connecting them to the vehicle’s metal chassis. You can test they are correctly grounded by checking they show resistance readings on an ohm meter below 2 ohms. 

Before tuning your antenna, the final step is to check the standing wave ratio is as close to 1:1 as possible. This step normally confirms your antenna system is correctly mounted and grounded. Make sure your SWR reading is lower than 1:2 before starting to tune your radio. 

A reading higher than 1:2 won’t be improved by this fine-tuning stage of the process. You need to rectify the bigger issues indicated by SWR readings first. 

Once you have an SWR reading of ideally 1:1.5 or lower, you can now tune your antenna for optimal transmission quality across the 40 CB channels. 

Some CB radios have inbuilt SWR meters, but when you’re first tuning your antenna, it might be better to get an external SWR meter for accurate results. Once tuned, you can compare with the inbuilt SWR and use those readings going forward to check and re-calibrate your antenna from time to time.

How to Tune Your Antenna Using an SWR Meter 

The following summarizes the 6 key steps to successfully tuning your CB antenna:

  1. Get into a clear open space and close the doors and windows of your vehicle 
  2. Connect the SWR meter and turn on the CB radio
  3. Measure the SWR for channel 1
  4. Measure the SWR for channel 40 
  5. Assess the results. Is one SWR reading higher than the other, which one and by a lot?
  6. Adjust the antenna length according to the SWR results

To get the best antenna calibration, get out into an open space without trees, buildings or other metal poles or antenna in the near vicinity, and ideally no closer than 150 feet around your vehicle. Get into your vehicle and make sure the doors and windows are closed and that no one else is standing close by outside.

Connect the SWR meter to your CB radio. Turn on your radio and select the SWR setting.

To measure the SWR on channel 1, select channel 1. Key the microphone and note the SWR meter reading, and in particular, make sure it is less than 1:1.5. If higher, you’ll need to go back and recheck your antenna mount and connections. 

To measure the SWR on channel 40, select channel 40. Key the microphone and note the reading, and in particular, make sure it is less than 1:1.5. If higher, you’ll need to go back and recheck your antenna mount and connections. 

Assess the SWR readings. Are both readings lower than 1:1.5. Is one reading much higher than the other?

If there is a big difference between SWR readings on channel 1 and channel 40, it is time to tune your antenna by adjusting its length. If the SWR reading on channel 1 is higher than on channel 40 you need to shorten your antenna. 

If the SWR reading on channel 40 is higher than on channel 1 you need to lengthen your antenna. You adjust your antenna until the SWR readings are reasonably equal for both channels. It will rarely be perfect. Normally one channel is slightly higher than the other, so make the best, most practical, adjustments based on the equipment and antenna you have.

How Do I Adjust My Cb Radio Antenna Length (And Other Tips for Tuning My Antenna)?

The adjustments required for your antenna are only small, no more than a few millimeters at a time. Try adjustments of 1mm at a time to avoid overshooting the ideal length for your CB antenna. 

Lengthen the antenna by adding antenna segments. These come in several forms, including inbuilt extendable antenna sections, or using grub screws.

Shorten the antenna by removing or reducing antenna segments according to the design of the antenna. 

If your SWR readings are high, such as above 1:1.5 make sure the coaxial cable connecting your antenna to the radio is not coiled around anything or twisted up in any way. Keep it as straight as possible and ideally, the shorter the better.

Some of you may have two antennas on your vehicle. If these are for two separate radios, test them individually. Make sure they are as far apart as possible, and if possible, at different heights.

If in doubt go to your local CB radio expert shop or outlet. This is especially important if you can’t get your SWR readings below 1:2.

And if your SWR readings are above 1:3, don’t transmit over your CB radio, otherwise you risk damaging the output stage of the power amplifier, also known as the finals, of your CB radio.

These happen to be the most expensive part of your CB radio too.

Common Problems That Cause a High SWR Reading 

When you get SWR readings higher than 1:2, whatever the issue is, resolve it. Certainly don’t transmit if your readings are higher than 1:3. Identify and resolve the issue otherwise you might damage your CB radio. You can still use your CB radio to receive messages when the SWR is higher than 3, just don’t transmit.

Options to solve SWR readings include: 

  • Is your SWR meter connected to your CB radio correctly?
  • Have you got a good ground plane?
  • Is your antenna mount properly grounded?
  • Is your antenna optimally located? The more central the vehicle the better.
  • Is it the right antenna for your vehicle? If you don’t have a metal chassis on your vehicle, you may need a No Ground Plane antenna.
  • Are there any issues with your coaxial or grounding cables? Look for twists, bends etc. otherwise test and or try replacing them
  • Try difference antenna or mounting locations

What Is SWR and Why Is It Important? 

Standing Wave Ratio is the ratio of output power transmitted versus how much is reflected back. When the output power can’t transmit efficiently, the radio waves don’t radiate out the way they are meant to. The lower the SWR, the better your radio is at transmitting radio frequencies and the less they are being sent back to your transmitter. 

When the power is reflected back it normally comes back as RF energy which causes the finals to heat up. As these are normally the most expensive components of the entire radio, damaging these can be disastrous for the use, and repair, of your radio.

CB radios can only transmit 4 watts in accordance with FCC regulations. If a lot of this is being reflected back, you might be cranked up to 4 watts but only transmitting 1 watt. Small adjustments can therefore make a big difference and really improve your transmission.

Each of the 40 CB channels works at an optimal antenna length for that frequency wavelength. The antenna length you tune to is designed to get the best outcome for all 40 CB channels. If you tuned to just one channel because that is the one you use the most, you can optimize performance for that one channel, but you may reduce performance on the rest of the channels. 

The key message here is that antenna length is rarely optimal and tuning your antenna is really about getting the most out of the available length options.

Key Takeaways

Before tuning your CB radio antenna, take an SWR reading and make sure it is as close to 1:1 as possible and ideally no higher than 1:1.5. Only tune your CB antenna once you have reviewed and resolved any issues arising from a high SWR reading. 

When tuning your CB antenna, you only require small adjustments to the length of your CB antenna to have an effect on the SWR. If the SWR reading on channel 1 is higher than the reading on channel 40, shorten your antenna. If the reading is lower, lengthen the CB antenna. This way you can achieve optimal tuning to pick up all 40 CB channels on your CB radio equipment.

Paul Dudley
 

Paul is the owner and founder of WhollyOutdoor.com . His passion for ham radios and fishing lead him to create this site. He loves playing with his radios and doing many other outdoor activities