[TowerTalk] Multi-Op Station Interconnect coax type?

[Jim Brown]

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