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

To: "topband" <topband@contesting.com>
Subject: Re: Topband: Problem with compression F connectors on Quad RG-6
From: "Paul Christensen" <w9ac@arrl.net>
Date: Tue, 7 May 2013 10:33:00 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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.

It remained that way with Comcast & AT&T Broadband at least until 2002 when I left AT&T corporate engineering, shortly after the merger. I doubt much has changed since then.

Concerns are a bit different in the broadband world where downstream leakage must be minimized between 50 MHz - 1 GHz. The upstream path is in HF region, but no sane cable operator uses spectrum below about 10 MHz. The only services anywhere near that area of spectrum are used for data transponders and IPPV from the set-top box where modulation is almost always QPSK. Telephony and DOCSIS cable modem service is all relegated to an area above 20 MHz. In the Jacksonville Comcast system, it's now all above 30 MHz which was made possible through the use of tighter diplexer specs in the system amps and fiber-optic nodes. if you could see a spectrum analyzer display of the return path back at the headend, you would be amazed that the return path works at all. Any point of ingress results high levels of interference, most notably SWBC.

I recall writing up a paper in the mid-'90s that predicted a need for better return path certification and an upward move of the lowest usable frequency to well above 20 MHz. I pointed to the 11-year sunspot cycle as an important driver. The non-ham engineers in our group didn't get it. But the CTO of MediaOne was a ham, and he did get it. The public did not know it, but there was a real fear between 1995 and 2000 that return path broadband technology would never work. When you consider all the points of potential failure, especially on a power-passing system, it truly is a miracle that it works at all. Consider this: The typical fiber-optic node services between 200-500 home passings. From the comfort of your living room, and with an RF signal generator, one can wipe out an entire service area when the return path frequencies of the system are known. This isn't theoretical, I demonstrated the impact to a sober group of engineers with an Eico generator. That potential still exists today.

Concerning SANS connectors and wiring, I would take the lead from the cable operators. They cannot afford to have unreliable cables anywhere between the customer equipment and the headend or hub facilities. When you've got thousands of miles of cable plant and interfacing hardware, that becomes the most important piece in the network. If a router, modulator or fiber amp fails in the system, the fix is easy with money. But if you deploy bad cable and hardware into a system, you'll feel the pain a long time as it affects long-term service call volume, unhappy customers, and angry government leaders who generally hate the cable operators.

Paul, W9AC
All good topband ops know fine whiskey is a daylight beverage.
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