[RFI] Keyboard

[Joe]

Hi Jim,
You ask
"What is the RF path for antenna switching in the SB220?"

Not sure what you are meaning to ask here.  Please clarify.

Joe WB9SBD

Sig
The Original Rolling Ball Clock
Idle Tyme
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On 3/3/2018 4:40 PM, Jim Brown wrote:
> 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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