From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <1608d073056.marcocadeddu@tin.it> <d877cf2d-4e75-b372-9bd2-302791f416b0@n1bug.com> <4556666E6F7849679451F95BD8C43FAA@Clemens0811> <e0a831c8-5a4b-1734-335e-58d995fa004a@n1bug.com> <9dbb1de2-0d17-b64f-3051-fd63f1f29cc4@n1bug.com> <51D7E4AF62D34F388A618D1DEA4942D2@Clemens0811> <5ea52d97-4678-1781-e3b5-6f0d12c6a5fb@n1bug.com>
In-Reply-To: <5ea52d97-4678-1781-e3b5-6f0d12c6a5fb@n1bug.com>
Date: Fri, 29 Dec 2017 13:08:27 +0100
Message-ID: <CD9537379F1A4225B3D969AF85B7C1FF@Clemens0811>
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Subject: RE: R: Re: LF: TXing 2200m WSPR
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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: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of N1BUG
>Sent: Friday, December 29, 2017 11:40 AM
>To: rsgb_lf_group@blacksheep.org
>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
>
>
>---
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