Re: OK to use TV coax for microphone?

Jeff Liebermann wrote:
> 
> On Sun, 04 May 2008 11:11:40 -0400, "Michael A. Terrell"
> <mike.terrell@[EMAIL PROTECTED]
> wrote:
> 
> >Chris S wrote:
> >> If copper is soft then wouldn't that make it good for repeated
> >> flexing in the sense that copper isn't so stiff that it wouldn't
> >> split or crack?
> 
> >   Copper 'work hardens' when flexed. Over time it develops cracks,
then
> >breaks. Stranded wire uses smaller conductors and has less problems per
> >conductor, due to a larger bending radius VS the diameter of the
> >conductor.  The steel center conductor is meant for permanent
> >installation, but it holds up better on the bench that solid copper
> >coax.
> 
> Yep.  Way back in the 1960's, I was installing 2way radios in various
> vehicles.  Someone found some RG-58/u, with a solid center conductor.
> I was told to use it.  About 100 vehicles later, someone declared that
> solid coax was a bad idea.  Management decided that it would replace
> all the coax, but only after evidence of the first failure.  So, we
> waited, and waited, and waited.  I was long gone when one of the coax
> cables finally failed, about 5 years or 150,000 miles later.
> 
> Fast forward to the early 1990's and cellular telephone installs.  At
> the time, the average cell phone was big, boxy, heavy, and ugly.  The
> connector of fa****on was the TNC.  Once again, some dealers were
> installing solid center conductor coax in the vehicles.  They would
> last about a month and then break.  Huh?  Solid center conductor
> RG-58/u works in 100 buses for 5 years, but not in a passenger car for
> a month?  Something is obviously different.
> 
> It's the connector.  In the 1960's we soldered everything.  The common
> PL-259 and UG-175 adapter was as sloppy a connection that could have
> been mis-designed.  30 years later, everyone was crimping the
> connectors.  The breakage was always at the connector.  The crimper
> was dinging the center conductor.  The sharp edge on the rear of the
> center pin did the rest.  Soldering the center pin and the longer
> distance between the crimp and the point at which the cable will begin
> to flex (UHF versus TNC) did much to prevent breakage.
> 
> All RG-6/u "type" cables are not all solid center conductor.  Belden
> Brilliance 1694F is flexible.
> <http://www.belden.com/pdfs/Prodbull/NP233.pdf>
> at about $0.70/ft.  However, it cannot be used with Type-F connectors.
> The data sheet mumbles:
>    "1694F is intended for use with connectors designed for 1694A"
> which is not very helpful.
> 
> The foil outer ****eld usually tears in a flex test long before work
> hardening does anything to the center conductor.


   The early Raychem connectors didn't seem to have that problem, but we
used the 'F' to'G' adapters on the bench.  I went through about a set of
cables a year while repairing CATV equipment, over 10,000 repaired items
and some were plugged in several times.

> 
> I've watched cable flex testers locally:
> <http://www.ideinc.com/plan_cycle.html>
> <http://www.ideinc.com/plan_tester.html>


   We tested BNC, IDE, SMA, SMB, SMC, and several other connector types
of custom cables at Microdyne, prior to installing them in our products.


> (Bring hearing protection).  These simulate normal cable bending on
> telephone headsets.  The flexing is far more radical than anything
> that would be encountered with RF coax cable.  I asked if they had
> ever tried flexing RF type coax cable.  As I vaguely recall, neither
> solid or stranded center conductor coax cables survived for very long,
> but I don't recall the numbers.  I'll ask.


   The life depends a lot on the minimum bending radius. The smaller the
bend, the more either conductor is stressed. I always used cables that
didn't need tight bends, and long enough to let me flip an item on the
bench while repairing it.

 
> Incidentally, there's also the tiny triboelectric noise created by the
> mylar coated insulated ****eld, rubbing against the dielectric:
> <http://en.wikipedia.org/wiki/Triboelectric_effect>
> Good microphone cable should be "bonded" (i.e. glued) to prevent this
> admittedly tiny noise problem.  You're not going to find that in
> commodity RF coax cable.


   I never used coax for microphone cables, but I have lost count of the
number of 1000 foot spools of Belden two conductor microphone cable,
I've bought.


-- 
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with **** and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm