Tom,
you say:
>That's why I am not enamored with tunable PA's that have RF
>feedback from the output to the input in an attempt to decrease
>distortion. For every tuning condition where distortion is reduced,
>there is one where distortion is enhanced.
Interesting comment. I'm not totally sure that companies like Marconi,
Collins, Racal etc would agree. On the other hand, I may be trying to
apply your comment to auto tuned professional amplifiers running into
<2:1 SWR all the time, when you intend the comment to apply to ham radio
linears, which are a totally different situation. I did a 400 watt
marine linear a few ( er......... about 25) years ago where feedback
around the PA was very successful in pulling the IMD down: the
application is akin to amateur radio, since it used an end fed wire
antenna looking like about 10 ohms in series with between 150 to 300pF,
tune up on installation with a trimmer capacitor for the operator to
tune for maximum current. Even with the trimmer fully detuned, the IMD
was still better with the feedback. Now, it's true that such experience
with one particular type of equipment doesn't give a general caveat in
favour of feedback in tuneable PA's - additionally, it needs very
careful design. Refer again to my old friend 'Single Sideband
Fundamentals and Circuits.'
Thanks for the comments on the transformers, all.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|