Try asking over in the HeathKit_HFAmps group:
HeathKit_HFAmps-Subscribe@yahoogroups.com
Joe - W7RKN
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Jim Brown
Subject: Re: [RFI] Keyboard
On 3/3/2018 12:09 PM, Joe wrote:
> BUT I may have fixed it by accident. I have been in the process or
> bringing an old dead SB-220 back to life, and have put it inplace this
> morning, so cabling has changed greatly in the shack. And the problem
> may be gone now by just changing out all the cables?
Lots of problems like this are caused by a bad piece of coax, or coax with a
poor shield connection (or no shield connection). Under normal operation,
current on the center conductor returns on the shield, so the field stays
within the coax. When there's no shield connection, current returns on
whatever path Mother Nature finds, and there's a strong field OUTSIDE the
coax. That field radiates, and also magnetically
(inductively) couples to anything around it.
What is the RF path for antenna switching in the SB220? Many unwashed
engineers used the chassis as return rather than running coax. This creates
the same sort of problem inside the amp -- current returns on the chassis
rather than the coax shield, so it produces EM and magnetic fields. GOOD amp
designers use coax for everything in the RF path.
73, Jim K9YC
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