On Fri,12/26/2014 7:34 AM, Rich Hallman - N7TR wrote:
Looking to see if good quality RG213 / RG8 (95-98% shield) is ok past the amps
to the high power 4O3A filters or should I use something like LMR400 / BuryFlex
for those connections to keep down the potential inter-station interference?
EMC authority Henry Ott teaches that shielding provided by coax depends
on the resistance of the shield and its uniformity. W2VJN, author the
the excellent guide to Managing Interstation Interference, noted in the
second edition that stubs cut from coax with shield construction like
LMR400 deteriorated over time sitting in his garage.
My advice would be to use RG8/213-size coax with from a factory that you
trust for excellent construction quality and having a dense copper braid
and low shield resistance. Shield resistance is, of course, a function
of skin effect, which in turn is a function of DC resistance and the
o.d. of the conductor. The measured parameter for shielding
effectiveness is the Transfer Impedance, which is the ratio of the
differential voltage inside the coax to the common mode shield current.
The lower limit on Zt is the shield resistance.
73, Jim K9YC
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