Topband: RG-6 Coax again

[Guy Olinger K2AV]

Part of the discombobbled nature of this RG6 discourse might have to do with
a lack of detail on failure modes, dissipation, etc.

With a long run, say 200 feet, running 1.5 K, and let's say dissipating 400
watts, that would be dissipating two watts per foot, or 0.17 watts per inch.
 If you placed your thumb and forefinger around that one inch somewhere, in
an outdoor setting you could not detect 0.2 watts worth of additional
temperature. The energy dissipation level of .025 watts per square
centimeter is just too far down.

That amount of power is clearly not destructive, either.  BUT, do you want
to lose 400 watts?  So the question, as always, is "Would you tolerate that
inefficiency in your amplifier?"  If your Alpha 9500 would only put out 1100
watts, you would have a conniption fit with the folks in Colorado.  And then
run RG6 out to your antenna?  Does the word schizophrenia come to mind?

The only other similar subject where our power aims seem this schizophrenic
is our inattention to 160m ground current losses on vertical radiator
antennas.

Burning up the RG6 is not the issue if it's run to a decent match at the
antenna.  It's the LOSS.  Most of that stuff has a copperweld center
conductor for strength, and an aluminum foil primary shield and the copper
is economically very thin as all of it was designed for VHF/UHF/SAT use,
copper just barely thick enough for VHF. On 160, skin effect is in the
steel. Then there's the aluminum foil.

Hams are an invisible microscopic portion of their customer base, and we
don't count for dink in their business model.  RG6 is cheep because they
make thousands of miles of the stuff in bulk for VHF/UHF/SAT, very carefully
engineered specifically for VHF/UHF/SAT.

I'm sure that we could get all copper center conductor with copper foil and
copper woven shield.  But then it's not cheep any more.

I'm not surprised that F connectors can carry QRO, because BNC connectors
can. It only has to carry four and a half amps at 75 ohms QRO, even less for
split feeds to phased antennas.  After all basically an N connector is a BNC
with weather proofing.  The question here is what happens when the connector
goes bad.  Is there enough contact area that it takes its time, or does the
sudden resistance with a very small contact area go up in smoke.  That's why
I stick with teflon/silver UHF connectors on HF.  A lot more staying power.


And then there's the argument that since I run 100 watts or QRP, it doesn't
matter.  Except the loss has a far more harsh effect on QSO rate as the
power level goes down.  Truth be known, it's the QRP operator that needs the
hard line, that needs the commercial BC radial field, for whom it will make
the most difference. Got nothing at all to do with burning stuff up.

73, Guy.

On Tue, Oct 18, 2011 at 1:40 AM, Robert Smits <bob at rsmits.ca> wrote:

> On Saturday 15 October 2011 07:47:01 John K9UWA wrote:
> > That would have been me Dave. I have been using Garden Variety RG6
> > on my 160 array for well over 20 years. I tested a single run of it with
> a
> > pair of heathkit dummy loads. Test piece of cable was 10 feet long with F
> > connectors to F-UHF adapters. Brick on the KEY on the Amp until the Dummy
> > loads started to smoke. Amp off and grabbed the coax. No heating observed
> > in the coax or the F connectors.
> >
>
> And how do you get it back down to 50 ohms for the transmitter.
>
>
>
> --
> Robert Smits bob at rsmits.ca
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>