Topband: Cable shields

[Tom W8JI]

>I suspect the corroded foil would have little measurable effect on the
> coax's shielding effectiveness for lower frequencies. The foil is
> primarily there for the higher frequencies, the braid for the lower
> frequencies (that's a generalization, but close).

I can put a number on that using two-year old indoor-use ComScope "Brite 
wire" ( I think that is what it said), which is a non-flooded dual shield 
(foil and braid).

160 -80 dB
80 -88 dB
40 -99 dB

I slit the jacket, removed the jacket to within about six inches of the 
connector, cut the braid, and bunched it near the ends so only foil was left 
over seven feet of cable.

160 meters went from -80 dB down to -78.25 dB, so removing almost the entire 
braid was worth about 1.75 dB out of 80 dB.

Keep in mind all the other cable I tested was old unknown condition cable, 
although the copper braid cable was still on the reel and stored inside, and 
was a nice shiny braid.

73 Tom