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?
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.
@@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.
@James-ci3lx Thank you so much. I will have to take some time to wrap my head around the math - I've got an old copy of the ARRL book from the 70's - I'm sure the physics are still the same today 🙂
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?
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.
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?
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.
@@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.
@@ElectronicsNotes LOL No.
@James-ci3lx Thank you James. One question though - why does the ATU get hotter the greater the mismatch if it is NOT absorbing reflected power?
@James-ci3lx Thank you so much. I will have to take some time to wrap my head around the math - I've got an old copy of the ARRL book from the 70's - I'm sure the physics are still the same today 🙂
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?
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.
Ok