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Jason Davidson - CB Radio Specialist

Jason Davidson

Over 18 years of hands-on experience with CB radios and installations.

SRF/SWR/CAL switch and SWR CAL Knob
What it does Changes what your meter is telling you.
Where to set it SR/F for normal operation, SWR/CAL for antenna testing

What is SWR and the SWR Cal for?

Many CB radios have a built-in meter for testing your antenna system. This testing process revolves around something called "S.W.R." or Standing Wave Ratio. Many Cobra CB's, like the Cobra 29 LTD Classic and the Cobra 29 LX, have both a switch, or a button, and an SWR CAL knob. Some radios do not have the SWR calibration knob and instead will automatically calibrate your meter (not the antenna!). We'll explain in easy to understand language what all of these functions are for, and how to correctly use them.

Testing your antenna system

Checking, and tuning your antennas SWR is important for two reasons. First, this is the easiest way for you to tell if your antenna system (coax + mount + antenna + etc) was properly installed. Second, if your SWR reading is too high (higher number = reflected, wasted power) then you can damage your radio. Considering how important both of these points are, you'll always want to check the SWR reading of your antenna system. Either by using the built-in meter that many radios have, or by buying an external SWR meter like our SWRKIT. What you are doing is making sure that when you transmit, your signal is passing through your antenna system like it should. If your SWR reading is too high then your transmit power isn't leaving through your antenna properly, and part of your radio's output power is feeding back to the radio. Remember, the closer your ratio is to 1:1 (standing wave ratio), the more optimised your CB system will be. Low SWR readings will provide a long lasting and better performing CB radio.

How do I check my SWR?

Checking SWR with radios that have an SWR CAL knob

  1. CAL Switch: Flip the SRF/SWR/CAL switch to CAL This changes what your radio's meter is going to tell you. Right now, we want it to tell us where the SWR meter is calibrated.
  2. SWR CAL Knob: Turn your radio to channel 20. Key your microphone and turn the SWR CAL knob until the needle on your radio's meter goes to the CAL mark on the top right of the meter. Unkey the mic when adjusted.
  3. SWR Switch: Now you've calibrated your meter. The next step is to get the reading. Flip your SRF/SWR/CAL switch to SWR.
  4. Get your reading: Key your microphone. Look at the bar or line marked SWR. On many radios, this is the top line. You should see the following numbers on the SWR line of your meter: 1, a space for 1.5, 2, and 3. If your SWR reading is below the 2 mark, your reading is within tolerance. If your SWR reading is below the 1.5 notch, your antenna system is working very well. If the reading is almost or exactly a 1, then your system is working as good as it can.

Checking SWR with radios that have built-in automatic SWR calibration (this is your radio if you have an SWR meter, but do not have an SWR CAL knob)

  1. SWR Switch: Your radio should have a button or a switch that says "SWR". Turn this on now.
  2. Get your reading: Key your microphone. Look at the bar or line marked SWR. On many radios, this is the top line. You should see the following numbers on the SWR line of your meter: 1, a space for 1.5, 2, and 3. If your SWR reading is below the 2 mark, your reading is within tolerance. If your SWR reading is below the 1.5 notch, your antenna system is working very well. If the reading is almost or exactly a 1, then your system is working as good as it can.

Now what do I do with this SWR number?

The answer depends on what your reading was, and what you are doing with your CB radio. If your reading was less than a 2, and you mainly use your CB for casual use, then you are done. Congrats! There is nothing else you need to do. However, if your SWR reading was above a 2, or if you want to talk on a different channel (or channels) or if you want to optimize your system for the best performance, keep reading.

How do I tune my antenna now that I have my SWR reading?

The process can be summed up like this. 1. Check your SWR reading. 2. Adjust something on your antenna. 3. Re-check your SWR to verify your adjustments. Here's a step by step process for setting or tuning the SWR on your CB antenna:

  1. Check your SWR: Write down the SWR reading on channels 1, 20, and 40 based on the instructions above.
  2. Adjust your antenna: If your SWR reading is higher on channel 40 than it is on channel 1, lower something on your antenna. If channel 1 is higher than 40, raise something on your antenna. If channels 1 and 40 are (about) the same, and your lowest reading is on channel 20, then you are done.
  3. Verify your SWR: In most cases you're looking for the same SWR reading on channels 1 and 40, with your lowest on 20. As long as your SWR is less than a 2 on all 40 channels, you're good.
  4. What about dual antennas?: The process is the same, just adjust both antennas at the same amount.

SWR Troubleshooting

I thought I tuned my CB to my antenna? This is a common misconception. To be very clear here: You are not tuning your CB to your antenna. Nor are you tuning your antenna to your CB. Instead, you are using your radio to CHECK your SWR reading, and then tuning your antenna(s) to your vehicle. This is an important distinction! Your antenna is tuned to the ground plane your vehicle provides, and once you've set the SWR (aka tuned your antenna), then it is ready for any radio you want to use. Let me make that abundantly clear. Once you have a low SWR reading, you can use any CB you want. Your antenna is NOT tuned to your radio!
My SWR Reading is Higher than a 2 Follow the steps listed above and check your reading on channels 1, 20, and 40. If you find an SWR reading at or above a 2 on all channels, that may indicate something is installed incorrectly, or broken. You may need to replace your coax cable, mounts, and antenna(s) to resolve.
What do I DO to my antennas to adjust them? First, check your antenna's package for the specific instructions for tuning. The Firestik FS series CB Antenna, and other similar fiberglass antennas, have a screw at the top of the antenna. Adjust this up or down based on your SWR readings. Some fiberglass antennas do not have a "tuneable tip", with these "cut to tune" antennas like the Firestik KW series CB antenna you need to remove the antenna's cap, then cut off the outer insulation until you can get to the copper wire. Cut this wire down to tune (if your reading on 40 is higher than 1) * it's not uncommon to have to remove A LOT of copper wire to get these antennas tuned. For steel whip antennas, like the Wilson 2000 Trucker Antenna, you may need to use bolt cutters to trim the "whip" portion of the antenna. Remove the whip from the holder (held in with set screws) and either move up or down according to the readings. If your readings tell you to go down more, you will need to cut the whip with bolt cutters. (this is pretty common).
My radio's SWR light or "ANT" light is coming on? This means your SWR reading is too high and you can damage your radio by talking. Either attempt to tune your SWR using the steps above, or start replacing your antenna system parts until it's resolved. If you're near Iowa, come visit us and a technician can test your antenna system and find out what's actually going on.

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