Having once had two SB220 Heathkit amps (one, I devoted to 160-meters
only), coaxial cable is used for both the input and output. Further, the
braid is connected to chassis at BOTH ends of all coax runs. Heath did it
correctly.
Dave - WØLEV
On Sun, Mar 4, 2018 at 5:33 PM, Gary Smith <wa6fgi@steeltrails.net> wrote:
> 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
>> The Original Rolling Ball Clock
>> Idle Tyme
>> Idle-Tyme.com
>> http://www.idle-tyme.com
>> 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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>>>
>>>
>>>
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--
*Dave - WØLEV*
*Just Let Darwin Work*
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