Hi Rick,
K6, the relay that interrupts the keying loop (the exciter in / exciter
out path) in the 253 is located on the the same PCB as the KW (SWR)
Bridge. In my opinion the keying loop traces are way too close to the
high power RF paths on that board. When I had my keying loop running
through my 253 I had some difficulties too. Removing the 253 from the
loop made the keying problems go away, but then the 253 no longer has
the ability to prevent keying when it detects a high SWR or other fault
condition. I thought about trying to make some kind of a shield out of
copper sheet or PCB material, and installing it between K6, R7 and rest
of the components on that board. I have not tried it yet.
My guess that RF pick up by the keying loop as it passes through the
81486 board is causing the problem does not seem to be supported by the
fact that you could make the problem go way by wiggling the cables or
resoldering connections. Still I think it would be better if there were
some shielding between the RF and keying loop on that board.
N6KB
> I've been having an intermittent problem with my keying loop.
>
> After some frustrating sleuthing, I tracked the problem down to the 253. It
> seemed that if I lost the keying loop all I had to do was wiggle the Exciter
> IN/Out cables on the 253 and I was back in business.
>
>
> Since the problem occurred even while the 253 was in Bypass it suggested the
> Exciter In/Out jacks or, even more remote, relay K6 was the likely problem.
>
> It was a fairly painless job to partially extract the appropriate board
> (81486) and resolder the jacks and relay. In addition I built-up the centre
> conductor on the RCA jacks.
>
>
>
>
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