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.
More information about SWR and how to reduce the effects of high SWR levels: www.electronics-notes.com/art...
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[@mikeymouse4629]

Thank you for this information - very well presented.
But my understanding or SWR ( the amount of power reflected back to the TX) suggests that the higher the SWR, the less of the original TX power is actually being radiated.
So, if you have a high SWR (say 6:1), and you use an ATU to bring it down to say 1.1:1, all you are doing is using the LC circuits in the ATU to absorb the reflected power before it can get to the TX and damage the finals.
The ATU may make the TX see an SWR of 1.1:1, but if you put an SWR meter between the ATU and the antenna, you will still see an SWR reading of 6:1 (in the case above).
So the ATU basically 'protects' the finals in the TX, but there is still significant loss of transmitted signal at the antenna - am I correct?

[@ElectronicsNotes]

This is a good point. However if the ATU provides a good match between the transmitter and the overall antenna system including the feeder then in turn it will cause the power to be reflected back towards the radiating element of the antenna where it can be radiated. HF antennas with open wire feeders can operate very efficiently with high levels of SWR. The issue is that each time the power is reflected there will be power loss. Coax cable gives good screening, etc but introduces a relatively high level of loss. Open wire feeders when used correctly have much lower levels of loss snd can operate effectively in this mode.
I hope this helps.

[@mikeymouse4629]

@@ElectronicsNotes I understand your point about 'high swr being reflected will be radiated'., but in the case where you use an ATU to reduce the swr that the TX sees, and thus protect the final amps on the TX from overheating, the 'absorbed' rf energy just goes into heating the LC circuits in the ATU, and does not make it back to the antenna to be radiated.
The scenario you describe is the case where there is no ATU to artificially 'resonate' the antenna-feedline by absorbing the reflected power in the LC circuits of the ATU.

[@agustiana1247]

Ok

[@johnishikawa2200]

So the idea then, is that standing waves are NOT desirable on the feeder - coax or other type - whereas on the other hand, we WANT standing waves on the ANTENNA, as this phenomenon facilitates the radio waves detaching from it and then moving out into space. Ball park?

[@ElectronicsNotes]

Standing waves in themselves are not a problem. The issues arise because they can cause high voltages and current levels - this can be bad for a transmitter if the mismatch and high voltages / currents are seen by the transmitter (the levels are unlikely to cause problems with a feeder, but this could be possible if it is running very close to its limits). Also the power that is reflected backwards and forwards when standing waves are present suffer losses. This means that the signal can be attenuated. However soem antennas use an open wire feeder where feeder losses are very low and the standing waves are perfectly acceptable.
I hope this helps.