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

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Subject: Re: [Amps] Phase and amplitude of 2 tube amplifiers
From: Conrad PA5Y <>
Date: Thu, 13 Oct 2022 17:39:20 +0000
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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 <<>> On 
Behalf Of Conrad PA5Y

Sent: 13 October 2022 14:37


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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