Re: "Tek scope Jan1971 issue


Microphone cables and other pro audio cables still use the neoprene jacket
with fiber filler (Belden #8412). It's been said to absorb a fork lift
running over it. I believe that the string filler was to strengthen the
cable for pull and crush resistance. It would be undesirable for the
conductors to rotate or slide over one another within the sheath. In low
impedence (microphone)instrument cable, there are 2 conductors in a twisted
pair and that relationship has to be maintained. What determines the
stiffness in addition to the jacket and center insulator material is the
percentage of shielding and what style, (wound (most flexible) vs braided
for instance). I have seen HP instrument grade coax that has 3 braided
shields, one on top of another, for 100% shield coverage - but it is very

Mogami is a modern cable manufacturer with very nice stuff. Their audio
coax can be used in applications where a bandwidth of up to 10 MHz is
required (perfect for HDTV applications). The modern cable, I have noticed,
use much more and finer strands for the center conductor which contributes
to better bandwidth, flexibility and reliability.

-----Original Message-----
From: Craig Sawyers []
Sent: Tuesday, December 30, 2003 3:38 PM
Subject: RE: [TekScopes] "Tek scope Jan1971 issue

It is
possible that same requirement led to use of this stiff material for cable
coating that you are talking about.
What you need is cable specified as "TRS" grade, standing for "Tough Rubber
Sheathed". It is great stuff, black and really flexible - coils nicely for
storage. Much better for older gear than PVC sheathing which is really

Other possibilities are heat resisting cable, used for things like domestic
irons which also need high flexibility; this is silicone rubber sheathed,
and again a whole lot nicer than PVC.

All of this is more expensive (2 or 3 times) than PVC of course - but the
difference doesn't break the bank in the sort of quantities that we all use.

The older cables seemed to use quite a lot of string filler between the
cores, which allowed the individual cores to slide over one another inside
and relative to the outer sheath. Modern cables don't seem to do this any
more - probably a cost thing, like using PVC insulation - but increasing the
cable stiffness.


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