From: N1BUG <paul@n1bug.com>
To: rsgb_lf_group@blacksheep.org
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Message-ID: <ca6ecd65-32d9-340c-032b-a4ba8f1e9ae6@n1bug.com>
Date: Fri, 29 Dec 2017 06:13:03 -0500
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Subject: Re: R: Re: LF: TXing 2200m WSPR
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One final thing.

Thought maybe something in the antenna was breaking down (arcing or 
corona), so made another check:

I now have the capability to run the PA on 13V or 19V. At 19V I can 
make more power into the antenna before the signal goes dirty, 
compared to 13V. RF power is RF power. If it was something failing 
in the antenna system I think it should happen at the same RF power, 
no matter what DC supply voltage I use on the PA...

Paul


On 12/29/2017 05:40 AM, N1BUG wrote:
> 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
> 
> 

-- 
Paul
N1BUG  160m-2m         DXCC Honor Roll
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