[Amps] Phase and amplitude of 2 tube amplifiers

[Conrad PA5Y]

I have had some very interesting replies.



However, I should clarify that I have been running CP on 144MHz EME since 2015 and with good success. I fully understand the implications of this and that there is a 3dB loss from CP to linear polarisation. However, on TX it means that you are always heard no matter what spatial offset is present but most importantly the effect of Faraday rotation is largely negated. There are ways of compensating for the 3dB loss, I expect that the readers of this group will understand how 😊



I have also looked at the effect of phase and amplitude errors in a simplistic way and I know that less than 15deg phase error is perfectly acceptable. My TX hardware from the shack to the antenna is proven. With a single amplifier and a 2 ways splitter I already produce excellent CP.  What I must do is match the phase and amplitudes of 2 amplifiers. That is what I am interested in and from the replies I have had so far it appears that this should be possible.



I would be most happy to hear from anybody who has experience of phase and amplitude stability of tetrode amplifiers at VHF or above. There are many experienced members of this group.



Many thanks

Conrad PA5Y







-----Original Message-----

From: Amps <amps-bounces at contesting.com<mailto:amps-bounces at contesting.com>> On Behalf Of Conrad PA5Y

Sent: 13 October 2022 14:37

To: amps at contesting.com<mailto:amps at contesting.com>

Subject: [Amps] Phase and amplitude of 2 tube amplifiers



I am going to attempt to use 2 identical monoband tube amplifiers to generate CP but before I start I have a question. The 90 deg delay for CP comes from the array orthogonal physical boom separation. So the amplifiers must be in phase at the outputs.



I presume that this has been done in broadcast applications and I would like to know, assuming everything is tuned correctly how close the phase likely to be?



I have line stretchers for the inputs, I have extremely good phase matching on the Wilkinson splitter and 2 identical directional couplers that I have tuned for good phase and amplitude matching. I can also measure the relative amplitude and phase of the 2 amplifiers accurately. Small phase and amplitude adjustments are ok but I have no idea what to expect with tube amplifiers.



This was not really planned but a 2nd amplifier became available, so I thought why not? The tubes are becoming scarce so this way I can be a lot more gentle on them.



Regards, Conrad PA5Y





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