On Dec 16, 9:42*am, Bob wrote:
Hi,

Thanks for help; appreciate it.

I wasn't too clear.

By the "inner shield," I mean the signal carrying innermost (solid)
conductor of the coax.

Guess I am wondering how can emi noise get thru the outer shield and to
the signal carrying conductor. Unless, of course, it's a really poor
outer and leaky outer shield.

Regards, and thanks again,
Bob
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On 12/16/2010 7:49 AM, Cecil Moore wrote:



On Dec 16, 6:14 am, *wrote:
Can't picture how an emi source field would/could "get-thru" the coax
shield to the inner conductor.

It doesn't have to. The inner shield and outer shield are shorted
together at the chassis. If noise exists on the chassis, i.e. the
chassis is not really "ground", the result is differential noise on an
unbalanced input. Essentially the same thing happens when SWR meter
readings are affected by common-mode signals during transmit or when
an unbalanced antenna analyzer is connected to balanced feedline
without a choke. A good choke on the coax near the chassis often
reduces the magnitude of the problem in all of the above cases.
--
73, Cecil, w5dxp.com- Hide quoted text -

- Show quoted text -

Lets try the simplest expalnation first. If you are familar with RF
current flowing on the outdside of a coax cable during transmit(often
discussed here) it is the same thing but in reverse.

Jimmie