I have, a few years ago, seen ferrite material that was extruded into
flexible hoses. Darned if I can remember what for. Came from one of the
shielding outfits like Chromerics or somebody. Potentially, that could be
treaded over an antenna cable - but it was somewhat brittle if you whacked
it a good one. (Much like my dog)
Gary
-----Original Message-----
From: [email protected] [SMTP:[email protected]]
Sent: Monday, November 16, 1998 8:32 AM
To: [email protected]; [email protected];
Robert Bonsen
Subject: RE: ANSI C63.4 -- ferrites
Bob:
You stress the importance of discrete ferrite absorbers placed
closely along the antenna cable. The obvious extension of this thought is to
have a special antenna coaxial cable which has ferrite material continuously
distributed along its external surface.
Is this a reasonable extrapolation of the discrete ferrites
technique? Or does there have to be at least some spacing between discrete
absorptive elements?
If a continuous absorptive layer on a coax cable is a good idea,
then has anyone ever encountered such a cable?
Might there be some practical way to fabricate a flexible "add-on"
absorptive sleeve, possibly like the urethane foam thermal barriers placed
on water and refrigerant pipes?
Regards,
Ed
------------------------
From: Robert Bonsen <[email protected]>
Subject: RE: ANSI C63.4 -- ferrites
Date: Fri, 13 Nov 1998 17:02:52 -0600
To: [email protected], [email protected]
>
> In my experience when doing testing of semi-anechoic chambers for
NSA
> performance using ferrites is a must to avoid measurements being
influenced
> by the vertical drop portion on both the transmit and receive end.
Using a
> spacing of about half a foot inbetween individual ferrite beads
has worked
> best for me. Especially in the lower frequencies, up to about
150MHz, the
> effect of the cable drop on vertical pol measurements is
considerable
> (sometimes more than 1.5 dB). Thus, in all the NSA test
specifications I
> write, I insist on the use of ferrites.
>
> Of course, not using ferrites on the vertical cable drop allows a
chamber
> tester to tweak the cables such that at a specific problem
frequency the
> vertical cable drop portion acts as a reflector to reduce or
increase the
> transmitted/received signal levels somewhat. This may bring a
chamber/OATS
> in spec which really isn't. Or bring it out if the tester is not
aware of
> the problem.
>
> For better repeatability and better NSA measurements, ferrites are
> required. They do not make the cable totally RF-invisible but do
> considerably reduce the influence of the cable on the
measurements.
>
> Regards,
> -Robert
>
> Robert Bonsen
> Principal Consultant
> Orion Scientific
> email: [email protected]
> URL: http://www.orionscientific.com
> phone: (512) 347 7393; FAX: (512) 328 9240
>
>
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---------------End of Original Message-----------------
--------------------------
Ed Price
[email protected]
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA. USA
619-505-2780
Date: 11/16/1998
Time: 08:32:01
--------------------------
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