[Lowfer] receive antenna transmission line maintenance

[pbunn at patbunn.com]

Jack Smith actually mentioned it to me. I normally don't bury it. I di like 
you do Doug, but this went in late  in the summer so I cut a little trench 
with an edging tool. Must have slightly damaged it. Should have used filled 
cable but that stuff is messy as heck.

Todd,

I have a house at Edisto Beach that is probably line of site or near so to 
you. Have a salt water creek in the back yard. I have though about a short 
vertical transmitting antenna with the base in the creek. The power line 
noise there is awful though.

Pat


-----Original Message----- 
From: ToddRoberts2001 at aol.com
Sent: Saturday, January 26, 2013 8:41 PM
To: lowfer at mailman.qth.net
Subject: Re: [Lowfer] receive antenna transmission line maintenance

Thanks for the report on the corrosion problem with aluminum coax  shield
made worse when a DC bias is applied like when powering an active whip
outdoors through the downlead.

It makes me think it would be best to avoid using any coax with  aluminum
shield if you expect to use it for powering a remote active whip  outdoors.

I always recommend using a full-size RG213 coax with a remote active  whip.
Much better copper braid shielding compared to consumer-grade RG58 and
should be no
corrosion problems like can happen with aluminum shielded coax.

73 - Todd WD4NGG

In a message dated 1/26/2013 10:03:19 A.M. Eastern Standard Time,
pbunn at matrixei.com writes:

It makes corrosion worse. About a month ago I came in and found the power
supply led off on my DC coupler. I figured the power supply had died but
when I  unplugged the coax it was OK, so then I knew I was looking at a 
short
at the  probe or in the coax. Looking at the way the probe circuit works, I
didn't see a  way a failed transistor could result in a short  that low in
resistance.

I emailed Jack Smith and asked hid opinion and he said 90 %  likely that I
had  a coax problem and the DC bias would corrode a breach in  the shield.
After a couple hours with the multimeter, I found a pinhole in a  buried
section of the Belden quad shield. Just as Jack had indicated, the DC 
current
had caused the aluminum shield to turn to powder for s couple of feet. I
ended up replacing the entire 300 foot run with new  cable.

Pat
N4LTA

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