Hi Paul,
>I can try common mode chokes instead of isolation transformers, but
>will this really be better? Seems if the problem is common mode
>current the iso xfmrs should kill it...??
Basically yes.
But we don't know how much capacitively coupling there is between primary and
secondary
which might partially spoil the RF isolation.
I would just give it a try:
One chocke at the PA output is no big deal.
>I still have a couple of ideas to try: Replace 50uH choke in PA with
>different type core.
In Spice there's only a ca. +/- 0.5Vp voltage swing across the choke.
Hence the flux is less than 10% (3.7mT) of the max. flux for this core.
So no problem with that choke.
>Use completely separate bias supply.
In Spice it makes no difference.
73
Clemens
DL4RAJ
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of N1BUG
>Sent: Friday, December 29, 2017 11:40 AM
>To: [email protected]
>Subject: Re: R: Re: LF: TXing 2200m WSPR
>
>During the night I made a few more tests...
>
>Iso xfmr at PA output. 14T:14T on FT-114-JC core. Made the problem
>slightly WORSE.
>
>Iso xfmr at amp input. 4T:4T on 3 x BN73-202. Made the problem
>slightly WORSE.
>
>Removed iso xfmr from amp output, left iso on PA input. Slightly
>better than without iso anywhere, but still bad.
>
>Tried again all configurations of iso xfmrs (at antenna, at PA
>output, at PA input) using HP 3325B to drive the PA. No difference
>from using the Ultimate 3S.
>
>When I use an iso xfmr at the antenna the problem is WORSE than when
>I have the coax connected to the antenna ground. It's not a big
>change, but measurable and repeatable.
>
>Considered this might be an instrumentation problem with RF
>affecting the HP 1980B oscilloscope, but I can see the signal
>quality degrade in a receiver when the problem occurs so I don't
>think so.
>
>I can try common mode chokes instead of isolation transformers, but
>will this really be better? Seems if the problem is common mode
>current the iso xfmrs should kill it...??
>
>I still have a couple of ideas to try: Replace 50uH choke in PA with
>different type core. Use completely separate bias supply. However
>since the PA works perfect into a dummy load I am not sure the PA is
>the problem.
>
>I will try to make a shielded box for the PA. That will take some time.
>
>The Ultimate 3S is in the metal case sold for it. This is not great
>because of the paint (or powder coat) at mating surfaces. I will try
>to work on that but since using the HP 3325B as a PA driver does not
>make any change I have doubts this will help.
>
>Paul N1BUG
>
>
>---
>Diese E-Mail wurde von AVG auf Viren geprüft.
>http://www.avg.com
>
|
