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From: Dave Holford
X-Mailer: Mozilla 4.7 [en] (Win95; I)
Subject: Re: How to check for a 50 or 75 ohm connector
References: <firstname.lastname@example.org> <email@example.com>
Date: Mon, 23 Dec 2002 15:39:50 -0500
NNTP-Posting-Date: Mon, 23 Dec 2002 15:38:52 EST
Organization: Bell Sympatico
> F connectors leak RF in and out like a sieve. One of my old colleagues did
> extensive tests of 'transfer impedance' (this has nothing to do with
> characteristic impedance, but is a measure of screening) and could find
> nothing under the sun that had worse screening than an F connector.
While I am totally unimpressed by "F" connectors and would never use
them if almost anything else could be used, I have some difficulty with
the leakage stated above.
If that is true I find it unlikely that their widespread use would be
permitted in the vicinity of airports since cablevision systems commonly
utilize frequencies used for aviation communications and navigation
systems; and the prospect of all those connectors leaking RF at
frequencies used for Instrument Landing Systems would pose a very real
hazard to aviation safety. I can think of several locations where large
housing complexes and apartments lie within 1 mile of an ILS system and
no problems have ever been experienced with either localizer or glidpath
Also, I have at least 16 "F" connectors in my home and they are carrying
RF in the 144-148MHz band which is almost undetectable with several
sensitive receivers, unless the antennas are placed in close proximity
to one of the plastic cased devices attached to the system.
As to the continuing saga of the BNC. If the 50 and 75 Ohm connectors
were indeed incompatible I wonder why I have never encountered test
equipment with 50 or 75 Ohm restrictions? The organization for which I
worked for almost 30 years used vast quantities of test equipment in the
servicing and maintenance of 50 Ohm communications and 75 Ohm video
systems and I never recall ever seeing any piece of test equipment
restricted to communications or video systems - even in our research
labs. Just did a quick search of a couple of oscilloscope manuals and
can find NO warning about using the 'wrong' type of BNC plugs.
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