[RFI] just what everyone needs!

[Dale Svetanoff]

Christopher, Dave, and All,

First, my thanks to David, K1TTT, for posting the "docassist"  URL.  That
is very interesting, and I have downloaded not only the spec under
discussion, but several others in which I have an interest.  That web site
did not exist pre-2000 (I don't think), when we had to get mil docs from a
web site based in Philadelphia.  It was not all that well organized.

The most important data from the document is the table (and accompanying
plot) of attenuation per foot versus frequency.  Absorption losses are, in
fact, very low below 500 MHz, and rising to about 30 dB/foot at 1 GHz and
then to 18 GHz.  When combined with a shielded over braid, this would make
for a cable with very low radiated emissions in the UHF and microwave
region.  It should also be noted that this spec was cancelled in 2008.

The summary of all this is that even if you find a supplier for this wire,
without being made into a shielded cable, it will not do you a lot of good
unless UHF and microwave emissions are a problem for you.  (Yes, the
military has some tough radiated emissions specs for equipment, that
includes systems, so having a wire/cable that suppresses these emissions
had to be a help in meeting these specs.)  It won't help you on HF and VHF.


On a related note, back in the 1990s, I was Chair of an IEEE standards
writing working group making major revisions to IEEE Std-299, which deals
with measuring the RF shielding effectiveness of shielded enclosures.  Some
of the working group members noted that coax cable with ferrite-loaded
jacket was a (then) new item available from at least one manufacturer, in
Europe, I believe.  We ran some actual tests using ferrite loaded coax (in
the outer jacket) to see if the ferrites affected readings being taken when
making measurements (the coax was being used to carry signal from a sense
antenna to a spectrum analyzer or EMI receiver).  Yes, it did, so we had to
specify use of cable that had continuous (or multiple load areas) on the
coax, as opposed to single point loading, because the ferrites caused
either suck-outs or reflections (depending upon frequency) when used within
an enclosure being measured.  Continuous jacket loading minimized these
effects.  Note that loaded jacket coax does not affect the signal within
the cable itself. 

73, Dale
WA9ENA


 


> [Original Message]
> From: Christopher Brown <cbrown at woods.net>
> To: <rfi at contesting.com>
> Date: 9/10/2012 2:25:53
> Subject: Re: [RFI] just what everyone needs!
>
> It is similar, though I have never seen specifics on what they use
> material wise.
>
>
> First time I saw it, it was refered to as "percap" or something similar.
>
>
> It is just normal wire/cable with RF lossy insulation.
>
>
> Not really that useful HAM wise as
>
> It is $$$, speciality item and making RF lossy insulation that still
> meets all the requires specs is not easy).
>
>
> The loss per foot is pretty low until you get above VHF.
>
>
> I have seen it used as power and low rate/analog signal hookup wire in
> some cellular and microwave gear, as well as general purpose hookup wire
> in large (build in place multi-rack) systems in high RF environments.
>
>
> As I recall, loss was < 1db per 100ft above normal wire around HF, ~
> 10db per 100ft by 2m, and getting into the 5 - 10db per foot range by
2GHz.
>
> I priced some 10ga once, ~ $10/ft in lots of 1000ft or less.
>
>
> On 9/9/12 9:09 AM, qrv at kd4e.com wrote:
> > Could the "resistive material" be powdered toroidal material?
> > 
> > Might one then twist it around a cable, or wrap it like a coil
> > at a specific point, and at certain frequencies might it absorb
> > RF?
> > 
> > Might the "22 gauge stranded (19/34), tinned conductor" be grounded
> > at one end and serve as a drain?
> > 
> > Could the combo, wrapped around a coax line, be effective in blocking
> > and draining ground-induced energy from lightning, snow-static, sand-
> > static, and other low-level EMP?
> > 
> > Would a twisted pair of these be useful to carry a control voltage
> > to or from a tower - impervious to ingress from near-field high-power
> > RF?
> > 
> > Just speculating ... the physics is way beyond me.
> > 
> >> Believe it or not... its actually a mil spec item.  I did some
searching and
> >> it is mil-c-85485/5 which you can see at:
> >>
http://assistdocs.com/search/document_details.cfm?ident_number=34825&StartRo
> >> w=54901&PaginatorPageNumber=1099&status_all=ON&search_method=BASIC
> >>
> >> It has a 3 layer insulation with some kind of absorber in the middle
layer,
> >> they don't say in the spec but I would assume its probably some kind of
> >> resistive material.  They also say something about it only being
effective
> >> when used as a component in a shielded cable, so its probably not what
you
> >> want to run out and buy a bunch of to play around with.
> >>
> >>
> >> David Robbins K1TTT
> >> e-mail: mailto:k1ttt at arrl.net
> >> web: http://wiki.k1ttt.net
> >> AR-Cluster node: 145.69MHz or telnet://k1ttt.net
> >>
> >>
> >> -----Original Message-----
> >> From: Dave Cole [mailto:dave at nk7z.net]
> >> Sent: Sunday, September 09, 2012 12:51
> >> To: K1TTT
> >> Cc: rfi at contesting.com
> >> Subject: Re: [RFI] just what everyone needs!
> >>
> >> Oh Dear God!
> >>
> > 
> > 
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