[TowerTalk] NON-INSULLATION STRIKES AGAIN! RG174 ANOMALLY

[K1TTT]

This sounded odd so I pulled out my belden catalog... and sure enough, right
at the beginning of the coaxial cable section are these 3 'low noise'
cables.

174/u type  8239  description: bare copper covered steel conductor,
polyethylene insulation, conductive layer, tinned copper braid shield, black
pvc jacket.

58/u type  9223  description: tinned copper conductor, conductive layer,
polyethylene insulation, duobond II tinned copper braid shield, black pvc
jacket.

59/u type  9224  description: bare copper covered steel conductor,
polyethylene insulation, conductive layer, tinned copper braid shield, black
pvc jacket.

Note that these are separate from the 'normal' 174/u mil-c-17d  8216 cable,
and the common 58/u and 59/u entries.  Unfortunately this is common with the
'rg' numbering system, there are often many manufacture variations on those.
with belden you must check the 4 digit cable type to know exactly what you
have.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: D.W. Fearn [mailto:dwfearn at dwfearn.com]
> Sent: Saturday, September 05, 2009 00:40
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] NON-INSULLATION STRIKES AGAIN! RG174 ANOMALLY
> 
> I was using RG-174 as a shielded lead in a product we build and
> experienced exactly the same problem as Larry describes. This was
> from a brand-new, very expensive roll of Belden RG-174. This was to
> the grid of a tube, so even a very high resistance had an effect. We
> have changed to a Teflon-insulated coax and that solved the problem.
> 
> Doug K3KW
> 
> 
> 
> 
> 
> >Date: Fri, 4 Sep 2009 06:55:15 -0400
> >From: "Larry - K7SV" <k7sv at comcast.net>
> >Subject: [TowerTalk] NON-INSULLATION STRIKES AGAIN! RG174 ANOMALLY
> >To: <towertalk at contesting.com>
> >
> >Some of you may remember my posting about our experience with beverages
> >using plastic boxes to house matching transformers. The black plastic
> boxes
> >turned out to be conductive which obviously led to a lot of head
> scratching.
> >
> >Well, I've been working a small project using RG-174. I kept finding
> shorts
> >after putting connectors on the ends. Nothing was making sense so it got
> to
> >the point that I cut a foot long piece of the stuff, stripped back about
> an
> >inch of the outer insulated jacket at both ends and pushed the shield
> away
> >from the ends. I then took resistance measurements between the shield and
> >the ends (didn't strip back the inner insulation, just stuck the meter
> probe
> >in the end). So I'm still seeing resistance between the shield and the
> >center conductor.
> >
> >On a whim I connected a meter probe to the inner "insulation" at both
> ends
> >of the piece. Sure enough it was a conductive material. I picked up a
> couple
> >hundred feet of this stuff from Mendelson's at Dayton a few years ago. As
> it
> >turns out construction consists of an insulated black outer jacket,
> stranded
> >copper shield, a black conductive material, a light opaque insulation and
> >then the stranded copper inner conductor.
> >
> >My problem obviously existed anywhere that the inner black "insulated"
> >material was touching the shield.
> >
> >This is the first time I've experienced something like this with RG-174.
> >Actually as I think about it, the stuff must have really great isolation
> >between the center conductor and the braid! I don't think this is typical
> >RG-174!
> >
> >73 de Lar K7SV
> 
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> 
> 
> 
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