On Dec 16, 6:14*am, Bob 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