[RFI] Keyboard

[Gary Smith]

Tongue in cheek here, how bout out to the antenna?

Gary...wa6fgi


On 3/3/2018 4:16 PM, Joe wrote:
> 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
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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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