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From: bill@crystal.UUCP
Newsgroups: net.video
Subject: Re: Video connecting Cables
Message-ID: <391@crystal.UUCP>
Date: Thu, 10-Jan-85 16:49:14 EST
Article-I.D.: crystal.391
Posted: Thu Jan 10 16:49:14 1985
Date-Received: Sun, 13-Jan-85 06:47:06 EST
References: <117@lcuxc.UUCP> <1466@ritcv.UUCP> <897@amdahl.UUCP>
Organization: U of Wisconsin CS Dept
Lines: 47

> > I then replaced my rather nice-looking 75ohm cable (I got it with my VCR; it
> > has quick-disconnect F-connectors) with another shoddy-looking one that my
> > cable company had given me, and voila', the problem disappeared!!
> 
> Definately, beware of any of the "flexible" 75 ohm cables that you
> get with your vcr/disk. The shielding and the dielectric thickness are
> marginal at best.

Hear, Hear!  The patch cables my cable company provided were all 100% shield
(braid and foil shield), which I've found difficult to locate locally
in short lengths -- 500 feet is a little much.
The Radio Shlock ones don't have a shield spec, but they look to be lower
density than the 95% ones I've seen, maybe 80% or so.

Belden#  type    center  velocity  shield  cap./foot
9100     59/U    20gage    78%      100%     17.3pF  (1)
8241     59/U    22gage    66%       95%     21.0pF  (2)
RShack   59/U    22gage    75%       ???     15.5pF  (3)

	(1) is what my cable company uses;
	(2) is the only belden RG59/U coax available in < 500 foot spools;
	(3) is Radio Shack's coax.
The Belden 9100 has about the same loss as RS at 50MHz, improving to 2.2dB
better than RS at 900MHz.

Anyway, many of my reception problems were eliminated by throwing away the
cheap premade cables and replacing with 100% shielded ones. The quality of
the screw-type F connectors was probably also a factor.

>			I think every cable company that I have ever dealt
> with has re-broadcast local channels on the same cable channel.

You mean my cable system is doing something right!?  The only conflicting
local station is ch3, and they run a 24hour weather service on cable 3.

> Shoddy cables will pick up both the cable-tv signal and the regular
> broadcast signal, producing the above mentioned ghosts.
> 
Even an inch or so of twin-lead (300 ohm) cable can act as an antenna for
pickup of unwanted interference.  check leads on any adapters you might have.

-- 
	William Cox
	Computer Sciences Department
	University of Wisconsin, Madison WI
	bill@uwisc
	...{ihnp4,seismo,allegra}!uwvax!bill