[CQ-Contest] Station Re-Build - Coax

[Keith Dutson]

Thanks for the info.  Looks like RG400 is an excellent choice.

73, Keith NM5G

-----Original Message-----
From: CQ-Contest <cq-contest-bounces at contesting.com> On Behalf Of Jim Brown
Sent: Tuesday, March 12, 2019 10:48 PM
To: cq-contest at contesting.com
Subject: Re: [CQ-Contest] Station Re-Build - Coax

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





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