Hi folks,
I have a sample of just such a flexible ferrite loaded cable here in my
hand. I have had it for many years the intent being to use it for a
test site antenna feed. All I remember about it (and my memory is not
that good!) is that I believe it is of German manufacture. Any details
I had on this cable have been lost in antiquity. It is heavy, and
looking at it I think it is not meant for low loss applications.
Brief description based on my guestimate of dimensions.:
Center conductor 7 strands of about 22 AWG plain copper (large
diameter - nearly 2mm?)
Dielectric solid polyethylene
Single woven braid not wrapped very tightly also plain copper
Thin (0.5 mm ?) layer of ferrite material under outer jacket .
Overall diameter is just over 1 cm maybe 1.2 cm.
Given the weight of this two meter section I would not want it used for
the full length of the feed cable. There are no ID marking on this so
it might be a prototype, the outer jacket is grey with a blue stripe
running along it FWIW.
Now the capon type ferrites do not provide much attenuation over the
lower frequencies so this cable might not be effective where most needed
30 - 200 MHz.
So I would think that such cables are available but I have not
seen any other reference to them at least for commercial applications.
So someone should be able to find it.
Regards,
Colin..
Compaq
Maynard, MA
-----Original Message-----
From: ed.pr...@cubic.com [mailto:ed.pr...@cubic.com]
Sent: Monday, November 16, 1998 11:32 AM
To: emc-p...@majordomo.ieee.org;
randall.flind...@emulex.com; 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 <rbon...@orionscientific.com>
Subject: RE: ANSI C63.4 -- ferrites
Date: Fri, 13 Nov 1998 17:02:52 -0600
To: randall.flind...@emulex.com,
emc-p...@majordomo.ieee.org
>
> 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: rbon...@orionscientific.com
> URL: http://www.orionscientific.com
> phone: (512) 347 7393; FAX: (512) 328 9240
>
>
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---------------End of Original Message-----------------
--------------------------
Ed Price
ed.pr...@cubic.com
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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