Re: [IRCA] AC twin lead or speaker wire for lead in.

[Rick Kunath <k9ao@xxxxxxxxxxx>]

Patrick Martin wrote:
> Rick,
> 
> In my case the braid is not 100% coverage of the inter foil. The
> connectors are all well crimped on and very tight. But I don't have 100%
> shield from the braid at least. The foil may be 100%, but I have no idea
> how well it is on there. It is not glued anywhere, just wrapped around.

I am not surprised at your results then.

I had the chance to do a lot of cable testing when I was chief engineer 
of a cable television system and had to reduce egress. I tested a lot of 
cable.

Some of the stuff sold as CATV cable is such a poor performer that I am 
surprised it isn't illegal to sell it. It'd be OK for over the air, at 
least it wouldn't allow for egress and break any FCC regulations.

Based on your description of the cable, I am certain it is your problem 
with ingress. That folded seam-type shield is really ineffective at 
doing it's job.

The good news is that you can spot junk cable with ease if you just peel 
back the jacket and take a look at the shield, foil, dielectric and the 
center conductor.

You should be able to disconnect your antenna, connect a shielded dummy 
load, and see almost no ingress to the receiver with good non-hard 
shield (hardline) cable.

Based on your tests of the receiver, it is well shielded. How well you 
could test, if needed. If the ultimate rejection ability of the receiver 
shielding cannot cope with common-mode signals on the coax outer shield 
surface, as was mentioned, some grounding and/or choking at the receiver 
end will bring the levels to down to something the receiver can handle. 
The same may be needed at the antenna end if you see ingress there with 
the dummy load disconnected and the antenna hooked up. (Common-mode 
signal ingress control at the antenna end is critical too, otherwise you 
just have leakage there.

Hope this makes sense.

Rick Kunath


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