[OKDXA] Coax Replacement

Mon, 16 Sep 2002 22:43:54 -0500

Nelson,

Very fine job.  I was going to do something similar and you saved me a whole
lot of time.  ;-)

And just for the record.   I have repaired ailing amateur radio stations
around the world as well as long haul HF stations for the government.  Only
on two occasions did I ever find the coax to be at fault and in one case it
was the wrong coax for the use and in the other it had been manufactured
wrong.  The first was easy to find.  Someone had installed RG-8 in a 300ft
run to feed a UHF antenna.  (not good)  On the second, it was a tough
problem to find and I wouldn't have if it hadn't been for a first class TDR
that I applied to the line.  I paced off the number of feet to the problem
area, cut through the 2 inch hard line to find that the center conductor was
against the shield.

All of that having been said.  I have found many, many more problems with
incorrectly installed or faulty connectors.  I would recommend spending much
more time on the connectors than on the type of coax.

My 2 cents worth.

Coy
----- Original Message -----
From: Nelson Derks <[email protected]>
To: <[email protected]>
Sent: Monday, September 16, 2002 9:48 PM
Subject: Re: [OKDXA] Coax Replacement

> Ok I have heard who like what type of coax but why did you select the coax
> that you are using. PLEASE edumacate me.....

Ohhhh... Like we've never heard THAT before from The 'DLL...

By commercial standards, the original RG-8 coax was designed as a low-cost
50 ohm feed line in non-critical applications at moderate power levels. It
uses a durable solid polyethylene dielectric with a service life in the five
year range (really, look it up!). RG-213 is the mil-spec version with a
non-contaminating PVC jacket that extends the service life closer to 10
years. Old coax tends to go 'gooey' inside and will develop cracks in the
sheath causing water migration problems and loss of efficiency. RG-213 is
preferred, but there are cables sold as 'RG-213 TYPE' which isn't much
better than RG-8 in terms of durability.

In most cases, the selection is based on cost and usage. RG-213 is good
through 10 Meters for moderate run lengths and shorter runs up to 50 MHz. At
2 Meters and up, the loss characteristics become a factor and a foam coax
like Belden 8214 becomes attractive... But, even a good foam coax like
Belden has shortcomings in durability, heat resistance and impedance
accuracy. 8214 doesn't like hot attics or sharp bends and isn't the first
choice for phasing harnesses or tuned stubs, but, in a careful installation
it works well. Some Hams will sacrifice a few dB for the greater service
life of RG-213 over 8214, but, for a little more money, you can have it
all...

Check out the specs at: http://www.timesmicrowave.com/products/commercial/
for the LMR series from Times Microwave. These cables use a high silicone
content outer sheath that's extremely abrasion resistant (compared to
RG-213) and a high-density foam that approaches the crush resistance and
impedance consistency of a solid dielectric cable, while maintaining
superior loss characteristics. It's damn good coax and something you can
install once and pretty much forget about for many years. Everything I do on
2 Meters and up is wired with an LMR cable and I've had very good luck with
my VHF efforts. Part of that is due to the clean horizon on the slight ridge
at my QTH, but I do believe some credit must be given to the coax. I have
two runs that have been up five years and the outer sheath still looks new.

As for the model numbers, they come from the outside diameter of the cable.
LMR-195 is .195" like RG-58, LMR-240 is a quarter inch cable like RG-8X, and
LMR-400 is the equivalent of .405" RG-8 style cables. LMR-600 and up require
custom connectors, but offer even lower loss characteristics approaching
rigid Heliax style cables at a fraction of the cost. Visit the web page,
it's worth the time...

Also, rumor has it Doug Xander uses nothing less than LMR-800 and enjoys
superior results... I suspect you would too, if your QRP rig was running 10
gallons and had a Continental Electronics logo on the front panel, but
that's another story.

- AC5UP

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