Re: multishields in CATV was Re: [BULK] - [TowerTalk] RG-11 Source?

[Gary Schafer <garyschafer@comcast.net>]

Michael Tope wrote:


 Of course, unlike the pregnant CATV version, the Belden
> instrument was long and slender, properly terminated, and operated
> below waveguide mode cutoff :):) In either case, these shielding
> effectiveness numbers used to bother me because it was never clear
> how to relate them to absolute leakage levels. 
>
> 73 de Mike, W4EF...............................................

Look up "transfer impedance" on google. There are several articles 
describing testing cable leakage with a chamber.

It is also interesting to note that transfer impedance comes into play 
with solid shield cable too. This is also how lightning gets on the 
center conductor of a cable when using a shorted / grounded antenna 
element or a shorted stub at the top of the cable.

Current introduced on the shield of the cable has an IR loss in the 
shield material making one end of the cable shield at a different 
potential than the other end. This transfers to the inside of the shield.

73
Gary  K4FMX


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