How to Reduce the Effects of High SWR for Radio Transmitters

When using a radio transmitter for CB, amateur radio or for professional radio communications use people strive to get the best SWR in the antenna feeder. But it's not always possible to get the perfect 1:1 SWR reading. In this video we look at the effects of high levels of SWR - Standing Wave Ratio (or VSWR - it's almost the same thing as it looks at the voltages associated with SWR).

We also take a look at the methods of reducing SWR and how far to go as often the last 10% of improvement can take 90% of the time and is it worth it.

The video first takes a look at what SWR is and how it arises. In this way it is easier to understand how SWR can affect transmitters and the resulting effects on the transmitted signal.

There are some really useful tips that we provide to get the best performance from any radio communications transmitting system whether it is for two way radio communications, amateur radio communications, CB or any other form of radio communications transmission.

First try to get the best match between any coaxial feeder and the antenna system as this will ensure that the maximum amount of power is transferred and the minimum level is reflected back along the coax feeder with all the resultant losses that may entail.

Next, use an antenna tuner at the output of the transmitter - this though is more applicable for HF radio stations. The antenna tuner will ensure that the transmitter sees the best impedance match and the PA isn't subject to high levels of SWR. By doing this, it can prevent possible damage to the PA output devices or the reduction in power level when the protection circuitry starts to act.

The maximum level of SWR that many transmitters are specified to tolerate is 3:1, so keep well below this by using an ATU or improving the matching at the antenna itself . Keeping the SWR below a maximum of 2:1 or preferably lower is a much better aiming point. But once the transmitter is happy there is little benefit in getting the SWR down from, say 1.3 to 1 to 1.1 to 1, so don't worry too much about those last little improvements.

Don't totally rely on the PA protection as it is meant to be a last ditch circuit. Most of these circuits work very well, but very occasionally small time delays can mean that it doesn't kick in fast enough and damage may still result. It's not worth taking the risk and it is always best to sort any known problems first.

Finally, the use of high quality coaxial feeder is always a good idea as it will reduce the losses in the feeder and it will mean that more of the transmitter power reaches the antenna, although it will mean that the SWR level seen by the transmitter for any mismatch at the antenna will be high, but that will be the subject of another video.


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