Barry said his reply was rejected so forwarding this to the list for him. Mike W9MDB
----- Forwarded Message ----- From: Barry Jackson <zen25...@zen.co.uk>To: Black Michael <mdblac...@yahoo.com>Sent: Friday, November 13, 2020, 06:25:03 PM CSTSubject: Fwd: [wsjt-devel] FT-991A problem Hi Michael, This reply was rejected from the wsjtx-devel list. How I am supposed to remember which account I use for each ML I subscribe to is beyond me! -------- Forwarded Message -------- Subject: Re: [wsjt-devel] FT-991A problem Date: Mon, 9 Nov 2020 18:07:25 +0000 From: Barry Jackson <g4...@btinternet.com> To: Black Michael <mdblac...@yahoo.com>, WSJT software development <wsjt-devel@lists.sourceforge.net> CC: Barry Jackson <g4...@btinternet.com> On 05/11/2020 22:39, Black Michael wrote: > What happens if he turns the rig power and wsjt-x power all the way to > zero....no watts out. > > Sounds a lot like RFI. > > Also...try setting the audio out to the computer speakers and see if the > USB still drops out. > > Mike W9MDB > Hi Mike, Dropping the power to 'zero' in the program changed nothing, however I suspected that maybe a click or similar was still being emitted, at start of TX. Switching the audio to the computer card for TX in wsjtx did make a difference. Transmit cycles continued correctly with no loss of USB connection. The USB lead already had multi-turn ferrite chokes in each end, but I decided to look at the isolation provided by an opto isolator based device. It turned out that there was about 30pF between input and output grounds on the one I had, which series resonated with the in-line ferrite inductors and actually made matters worse. So, I put a parallel inductor across the isolator to form a tuned trap at 7 MHz. It was considerably better than just the isolator on most HF bands and it was 30dB down relative to 50 Ohms on 40m. Simple comparisons were made using a nanovna. This was duly dispatched and fixed the problem, confirming that the issue is most certainly RFI as you suspected. Thanks for your help. Barry, G4MKT
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