Tuning Your CB Radio Antenna

by Andrew Youderian

Photo by Andrew Youderian A basic SWR meter is required to tune a CB antenna. They are available for under $20 at most CB shops.

 

The most important and often overlooked step in installing a mobile CB is tuning the antenna. While a properly tuned antenna will result in strong radio performance, a badly tuned or untuned antenna can result in poor performance and can even damage your radio.

Before you start fiddling with the antenna, it's important to understand the basic theory behind tuning as well as the term "Standing Wave Ratio" (SWR).

What Is Antenna Tuning?

 

Tuning is the process of adjusting an antenna so that the radio's output power is turned into radio signals as efficiently as possible. In more tangible terms, it involves incrementally increasing or decreasing the length of the antenna. The goal of antenna tuning is to match the antenna's physical length with that of the radio frequency being used, so as to ensure optimal performance and transmission efficiency.

 

An antenna's efficiency is measured by the Standing Wave Ratio, or SWR, which represents how much of the radio's power is being turned into radio signals by the antenna. An SWR reading of 1.0 indicates that 100 percent of the radio's power is being transmitted, while a ratio of 3.0 means that only a third of the power is being transmitted by the antenna.

The goal of antenna tuning is to achieve as low an SWR reading as possible. While low SWR readings result in the best performance, high SWR readings have more worrying implications than poor transmission range. In fact, operating a radio at SWR levels above 3.0 can cause damage to the radio because all that excess output power is reflected back at the radio as heat, which can result in permanent damage to the unit.

 

CB Antenna Tuning Instructions

Enough theory - let's tune that antenna! To tune a CB antenna, you'll need to have correctly installed both your CB radio and your CB antenna. You'll also need an SWR meter and a coaxial jumper cable; both can be purchased for around $20 from most CB shops. Now for the step-by-step instructions.

 

1. Find an open area. Drive your vehicle to an open parking lot or field; make sure there are no trees, buildings or other obstructions within 15 meters. To ensure accurate SWR results, make sure everyone is in the vehicle and that the doors are closed when you take the readings.

 

2. Hook up the SWR meter. Disconnect the cable going to the antenna from your radio and attach it to the connection marked "ANT" or "Antenna" on the meter. Next take the jumper cable and attach one end to the radio and the other end to the connection marked "TX" or "Radio" on the meter. The SWR meter is now installed in-line between the radio and antenna.

 

3. Take SWR readings. You're now ready to take SWR readings. You'll be taking readings using both Channel 1 and Channel 40, with the goal of reaching the same SWR level - below 2.0 - on both.

Depending on your results, you'll have to do one of the following.

Photo by Andrew Youderian The back of an SWR meter has two connections to allow the meter to be installed inline between the radio and antenna.

 

Channel 1 SWR is greater than Channel 40 SWR. If the reading on Channel 1 is greater than the reading on Channel 40, your antenna is too short and you'll need to lengthen it. Most fiberglass antennas have a tuning screw at the tip of the antenna that you can loosen or tighten to adjust the length of your antenna. Nearly all other antennas allow you to slide a steel whip in and out of the base to adjust the antenna's length. In either case, make very small adjustments and then recheck the SWR readings on both channels. If your antenna has a weather cap that covers the tuning screw, make sure it's back in place before taking your SWR readings.

 

Channel 40 SWR is greater than Channel 1 SWR. If the reading on Channel 1 is less than the reading on Channel 40, your antenna is too long and needs to be shortened. Use the appropriate tuning feature, discussed above, to make the adjustment. (In the unlikely - and unfortunate - event that your antenna isn't easily tunable, you'll need to physically shorten the antenna by cutting it.) Make very small adjustments and then re-check readings on both channels. If your antenna has a weather cap that covers the tuning screw, make sure it's in back place before taking your SWR readings.

 

Tuning Goals

The goals of antenna tuning are (1) to achieve SWR readings of 2.0 or less on both Channel 1 and Channel 40 and (2) to match SWR levels on the two channels as closely as possible.

 

If you've properly tuned your antenna, congratulations! While other CB owners grow frustrated with poor radio performance, you'll be enjoying the superior operation and transmission range that only a properly tuned antenna can provide.