[CQ-Contest] Station Re-Build - Coax

[Jim Brown]

On 3/12/2019 7:23 PM, charlie carroll wrote:
> A couple very similar candidate cables are RG-400 and RG-303. RG-400 is 
> double shielded while 303 is single.

The quality of a cable shield can have a strong effect on crosstalk, 
very important in a multi-transmitter environment. This characteristic 
of a cable shield is quantified as its Transfer Impedance -- defined as 
the ratio of the differential voltage inside the coax to the common mode 
current on the shield. Small values are good, and the lower limit is 
resistance of the shield at the frequency of interest. The density and 
uniformity of the shield is another factor in transfer impedance. And, 
of course, Transfer Impedance varies with frequency.

Thanks to skin effect, the reduced shield resistance of large diameter 
coax contributes both to lower attenuation and lower transfer impedance, 
provided, of course, that the shield is dense and has very good uniformity.

73, Jim K9YC