Re: [IRCA] coax loss

["Chuck Hutton" <charlesh3@xxxxxxx>]

Garden variety RG6 runs 9 or 10 Ohms per 1000' of center conductor, so
Patrick's 75' length really ought to have about .75 Ohms of DC resistance.

I'd bet his meter is contributing to the "problem".

A "problem" it isn't - an Ohm or two in series with his 50 Ohm input won't
produce enough loss to be noticeable at all.


Chuck


-----Original Message-----
From: irca-bounces@xxxxxxxxxxxxxxxx [mailto:irca-bounces@xxxxxxxxxxxxxxxx]
On Behalf Of Craig Healy
Sent: Thursday, August 16, 2007 8:07 PM
To: Mailing list for the International Radio Club of America
Subject: Re: [IRCA] coax loss

> I have been checking out all of my RG6 this Summer with an ohm meter. I
> have found with 3 pieces of the coax (SW EWE,WNW EWE, and 1500'
> beverage) that the coax is a hair leaky. Maybe because of the age. 90%
> of it runs under the house for the SW EWE and beverage. Using an ohm
> meter in the RX1 scale instead of getting a full scale when shorting one
> end together (braid to center, I get anywhere from 2.5 to 5 ohms.testing
> on the far end,  so almost a full scale. Using the coax for MW use,
> would I notice any change if I replaced all of the coax?  The coax runs
> are about 75-80 feet each. I have an old 100 foot roll of RG59 I have
> never used. So rolled up I did the same check and got a full scale. Any
> thoughts?

2.5 Ohms doesn't seem out of line.  Just to recap, you shorted the far end
center conductor to the shield and then measured the near end, center to
shield?  For a run of 75 feet or so, I'd expect a few ohms.  Most RG6 has a
steel center conductor that's copper plated.  The resistance of steel at
lower frequencies is why it's not recommended for video use, for example.
At VHF, the skin effect keeps most of the signal on the copper plating.

I am surprised that the new RG59 didn't show the same or even slightly
higher resistance.  Did you notice any water getting into the RG6 and
connectors?  That could have worked down the inside and corroded the shield.

The cable isn't all that expensive.  I'd consider replacing it.  Take the
worst section and do a before/after on local daytime signals.  That'll tell
you just what you may or may not gain by the swap.

I am looking at using CAT5 ethernet cable.  It's cheap, and the balanced
design may help reduce signals leaking in and spoiling the antenna pattern.
However, that does require a balun to match the roughly 110 ohm balanced
impedence to the 50 or 75 ohm unbalanced coax connection.  Still, it's worth
the shot.  Home Depot sells indoor/outdoor CAT5 in 500' boxes.  If I have
time (and ambition) this weekend I'll make up a couple of baluns and a 150'
CAT5 test length to compare to some RG58 and RG6 lengths.

Dallas Lankford uses ordinary AC twin lead or speaker wire.  He says it
works better than coax.  With a balun, of course.

Craig Healy
Providence, RI

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