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Re: Topband: Mother of all ferrite common-mode coaxial chokes

To: <topband@contesting.com>
Subject: Re: Topband: Mother of all ferrite common-mode coaxial chokes
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Fri, 13 Jul 2012 12:08:18 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
> If ferrite isolators or beads have been determined to improve the shield 
> performance of a coaxial cable in your hamshack, something is 
> fundamentally wrong either with the cable (but most likely the connectors 
> at either end) or the shielded enclosure(s) its connected to.
>
> I've seen literally hundreds of improperly installed PL-259, type N and 
> BNC connectors.  Years ago I stopped allowing anyone to bring coaxial 
> cables into my shack because so many are improperly installed.

It seems Frank, Jim, myself, and many others are in exact agreement. This is 
because underlying science is universally logical and valid, and proven both 
by measurements and by time in thousands of commercial systems.

Because I use phono plugs that really have improper shield grounding 
integrity, and sometimes the pressure connections add a tiny bit of unwanted 
shield impedance to the groundplane of "the box entrance", I use high 
impedance beads on these particular cables. I also, as a practice, keep an 
eye on those connectors. I use those connectors by necessity, because 
several of my radios use phono plugs for external antenna ports, and there 
is no easy way to change connectors.

In some places, how we attach cables doesn't matter much at all. In other 
places, in particular inside the hose, small errors can create large 
problems. The building entrance is also critical, if we want to keep bad 
things outside.

Save the isolators for outside, where they might do something meaningful.

73 Tom


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