How To Check Your SWR

You're probably reading this page because someone recommended that you check the SWR of your CB antenna and/or adjust your antenna. This page will show you what you need to do, and show you what equipment you will need.

SWR stands for "standing wave ratio". I won't go into technical details, but the SWR is a measure of how well your antenna is matched to the radio. In general, a low SWR means that the antenna is matched well to the radio, and that everything is working properly. In general, a low SWR means that you will be putting out a stronger signal. In general, a high SWR can damage your radio. I say "in general", because there will be a few situations where these statements are not true. But for a typical CB radio setup, you want your SWR to be as low as possible. The lowest possible figure is "1:1". When you read that out loud, it is "one to one." 1:1 is perfect. A higher number, such as 2:1 or 3:1, is not perfect. In general, if your SWR is below about 2:1, you probably won't be able to detect any practical difference by getting it lower. If it is below about 3:1, you probably don't risk doing any damage to the radio. But if it gets much higher than about 3:1, then there is probably a problem that should be fixed. This page will explain how to fix it.

To measure your SWR, you will need an SWR meter. Some CB radios have one built in. They are not particularly accurate, but they are generally good enough. Again, it doesn't really matter whether you have a perfect 1:1. So you don't need an expensive meter capable of making exact measurements.

If you don't have a meter, either built in to the radio or a separate unit, then you'll need to buy one. Even the cheapest models will be more than adequate for the task. Here are some options at Amazon:

If you buy one of these meters, you'll also need a short piece of coaxial cable to run from the radio to the meter. If you don't have one, you'll probably want to buy a meter that includes the cable, as some of the meters shown above do. You can also buy the cable separately:

The length of this cable is not important.

The SWR will vary depending on the frequency (channel) on which you are transmitting. Therefore, it will vary slightly depending on which channel you are using.

To begin, you need to hook up the SWR meter as follows:

Disconnect the antenna connection from the back of the radio.
The cable going to the antenna (that you just unplugged) goes to the output of the SWR meter. On most SWR meters, this is the connector on the right side. I will probably be marked "output" or "antenna".
Run the coaxial jumper cable from the antenna jack on the radio to the other connector on the SWR meter. This connector will usually be marked "input" or "transmitter".

After you have it hooked up, the radio will function as it did before. You can leave the SWR meter hooked up permanently if you want. Or, you can remove it when you're done adjusting your antenna.

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As mentioned above, the SWR varies depending on frequency. Since you want to cover all CB channels, it is best to set it for the best reading in the middle of the band (channel 20). So tune your CB to channel 20 or a nearby unused channel.

To check your SWR on this channel, follow the following steps:

Set the switch on the SWR meter to "Forward". This is often abbreviated FWD.
Press the mike button to key the transmitter. The meter should move.
Adjust the knob on the SWR meter so that the meter reads at the very top of the scale. This spot on the meter is usually marked "SET" or "CAL".
Flip the switch on the meter to the other position: "Reflected" or "Reverse" (REF or REV).
Look at the reading on the meter. The number is your SWR. If it says 1.5, this means that your SWR is 1.5:1. Note that if the meter doesn't move at all, this means that the SWR is 1:1, and everything is perfect.
Release the mike button

If your SWR was below 2:1, you can consider yourself done if you want. In most cases, that's good enough. But since you've gone to all of this trouble, you may as well continue and make things as close to perfect as possible.

If your SWR is above 1:1 (in other words, if the meter moved), then you will need to adjust the length of the antenna. But you need to know if you need to make the antenna longer or shorter. To determine this, you should check the SWR on channel 1, and then again on channel 40.

If the SWR gets better on channel 40, this means that the antenna is too short, and you will need to make it longer. If the SWR gets better on channel 1, this means that the antenna is too long, and you will need to make it shorter.

For example, let's assume that the SWR on channel 20 was 1.9:1. On channel 1, it was 1.2:1. On channel 40, it was 2.5:1. In other words, it got better as you went to a lower channel, and got worse when you went to a higher channel. This means that the antenna is too long, and you will need to make it shorter. Simply find the adjustment on the antenna and shorten it. This is usually a set screw holding in the top element of the antenna. You would loosen the set screw, and move the top section in a small amount. Depending on the antenna, this could be a very small adjustment, such as a quarter inch.

For another example, let's assume that the SWR on channel 20 was 1.5:1. On channel 1, it was 2.0:1. On channel 40, it was 1.2:1. In other words, it got better as you went to a higher channel, but got worse when you went to a lower channel. This means that the antenna was too short, and you will need to make it longer. Again, you loosen the set screw and pull the top section out slightly.

You'll probably need to repeat the whole process a few times. Eventually, you will get the antenna set so that the meter doesn't move on channel 20 (SWR = 1:1), and only a slight movement on the outer channels (perhaps 1.5:1 or so). Again, as long as you can get everything under 3:1, there's little chance of damaging the radio. And you would probably not be able to tell the difference between 2:1 and 1:1.