Topband: Problem with compression F connectors on Quad RG-6

[Carl]

----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "topband" <topband at contesting.com>
Sent: Tuesday, May 07, 2013 9:48 AM
Subject: Re: Topband: Problem with compression F connectors on Quad RG-6


>> CATV installers use almost 100% quad shield in order to keep the signals 
>> inside and not cause interfering leakage (egress); FCC specs are adamant 
>> about that. These specs go back to the 70's. In more recent years the 
>> cable also must keep local RFI (ingress) out.
>
> While they do use tape foil shield cables, CATV systems rarely use quad 
> shield cables. As a matter of fact I just bought a bunch of drop cable 
> from a CATV system, and it is all single foil single braid. This is true 
> for the drop, which has a messenger strand, and the house wiring, which is 
> identical without a messenger strand.
>
> In the late 70's and early 80's, I was system's engineer at a company that 
> had dozens of small cable systems. We inherited some systems near an FM/AM 
> station that had a second harmonic on a local TV channel video frequency. 
> The former cable system operator had given up, after installing quad 
> shield and all sorts of special cables. 100% of their problems were 
> isolated power and CATV grounds, letting the AM signal loop through the 
> system, and the quad shield developing poor connections letting the FM 
> harmonic in. We ripped all that stuff out, and went with normal hardline 
> and good quality drop cable, bonded the cable grounds to the entrance and 
> breaker panels, and nearly 100% cured the system. We had dumpster load of 
> special cable that was nothing but connector headaches.
>
> The standard drop cable is a bonded foil with single braid, it has been 
> that way since the late 1970's. The current best grade is "Brightwire" by 
> CommScope. Any good cable will far exceed FCC specs without a quad shield. 
> Single-foil single-shield "Brightwire" has over 120 dB of external shield 
> current to center conductor current isolation on 160 meters, and it gets 
> better as you go up in frequency. I can't imagine anyone needing more than 
> 80 dB isolation outside the house, and maybe 100 dB if it is in a noisy 
> house.

Around here Comcast installers use TFC T-10 quad shield. Ive also seen PPC 
trishield used for satellite.

As you can easily see they list their cables by RF noise enviroment from low 
for standard dual shield, medium-moderate for premium dual shield, plus high 
for trishield  and quad for severe with these last 2 also rated for 2 way 
use.
http://www.timesfiber.com/TFC_Cable_Book_III.pdf
Go to Page 36

Dont let ANYONE tell you that the shielding type isnt important.

In the 80's I was an engineering manager for Wang Labs broadband networking 
R&D department and one of my responsibilities was qualifying all cable 
related components for outdoor and indoor use for moderate to severe RF 
enviroments which included nuclear carriers and plants, plus oil refineries.

There was a measurable difference between dual and quad shield as well as 
percent of braid coverage. These cables plus connectors were tested in the 
screen room in the Tempest group.
Tempest was a DOD/CIA Top Secret program tasked to minimize electronic 
signal ingress and egress from spies and saboteurs. Since I had maintained 
my TS Crypto clearance as a USN Reservist and as an engineering tech and an 
engineer for Sanders Associates who was a leader in Tempest technology, I 
had full access to the testing.

I have also applied that knowledge at home for ham and consumer products 
ever since. It was Tempest starting in the mid 70's that gave me an 
understanding of ferrites for RFI, etc and that was applied to Wangs network 
as well as at home where I continue to do mortal battle with noise 
generators and common mode.

Carl
KM1H