Please note: These tuning instructions were specifically written up to detail ONLY tuning of 26/27MHz CB Radio and also 10m (28 - 29MHz) amateur band & possibly 2m (144 - 148MHz) band aerials. The tuning method is essentially the same procedure for vertical whips across the spectrum but the higher up the frequency the shorter the wavelength so the less an aerial may need to be trimmed

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 (or VSWR), 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.
 

The SWR is considred 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 similiar 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 similair. 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. You may find the SWR higher up the ends of the band for instance, don't be worried if it's "1.1:1" on channel 20 and then "1.7:1" on 40. If this is the case it just implies that the antenna is not very wide band.
 
 

'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.

'Itron' Base station aerials don't require tuning!

Pictured here is a specifications sheet that came with an aerial I recently purchased.  Power handling capability, frequency coverage, radiation type etc.  This aerial comes pre-tuned from factory, it may still required some tuning but I just screwed it onto the base and it was under 1.5:1 across the whole band. For more information on tuning aerials please visit http://www.mobileone.com.au/antennas/tune.htm