Standard Wave Ratio

Please note: These tuning instructions are specific ONLY to 26/27MHz CB Radio and also 10m (28 - 29MHz) amateur band & possibly 2m (144 - 148MHz) band. Do NOT apply this method on UHF or VHF aerials. Most VHF / UHF bands use DIFFERENT SWR meters than 27MHz CB.

These instructions are designed only for 27MHz CB Radio.

When you operate a CB radio, you are of course emitting radio waves which are electromagnetic signals coming from the radio and then aerial. However, the aerial has to match the radio to make a complete communications line, you can't just slap a wire on the end of the radio and expect to get around the world!

Due to this fact, there is a term denoted SWR, which stands for Standing Wave Ratio. That's all I'll say about that, because I'm here to tell you how to use it, not what it is. An SWR meter connects into the co-axial cable in series with the radio. It would usually consist of a knob to turn and needle driven meter to read.

SWR meter connection SWR meter

The SWR is considered a ratio, and the closer 1:1 it is, the better! Firstly, the meter will have a calibration setting (probably controlled by a switch) denoted SWR or REF or something similar on the scale and you have to adjust the needle on the meter while transmitting. TO do this you depress the transmit button, and adjust the knob until the needle on the meter reaches the designated point which should be indicated. If this doesn't work properly, then you have a problem!

Once you have calibrated the needle stop transmitting, then you have to switch the SWR meter to the other mode which may be called reflection (REF) or SWR or something similar. Then you may re-commence transmission and you will be indicated the SWR. It should be no greater than about 1.5:1 or so.

If the ratio is greater than 1.5:1 across most of the band you will have to adjust the aerial. Some aerials come with screw adjustable tips for easy tuning, just loosen the screw and lower the tip a little. Some aerials are wire-wound, and you have to take the cap off the top and snip a bit of aerial wire off. Only cut 1mm or so at a time. Once you have adjusted the aerial length you have to check the SWR again from scratch. That is, re-calibrate the meter and check the SWR.

'Station Master' Base Station aerials with the coil at the bottom may require tuning. To tune them, adjust the position of the wire that is screwed onto the coil, and that will alter the tuning, follow the same procedure with operating the SWR meter.

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This Web page was last updated on Friday September 21, 2001

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