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Re: [RFI] can a tower re-radiate RFI?

To: rfi@contesting.com
Subject: Re: [RFI] can a tower re-radiate RFI?
From: David Robbins <k1ttt@verizon.net>
Reply-to: k1ttt@arrl.net
Date: Mon, 25 Jan 2016 07:14:08 -0600 (CST)
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
DANGER WILL ROBINSON!!!  that could be a very dangerous situation... get a 
qualified electrician and the power company there ASAP and get everything 
checked out.  I had a neighbor who went through that and it was the ground at 
the transformer going to their meter that was bad, they blew all sorts of 
stuff, replaced it, and blew it up again before it was found.  don't trust a 
single voltage reading on a circuit to be correct either, as long as the loads 
are approximately equal voltages can look ok, then have one motor start, even a 
refrigerator, and it can swing the voltage on both circuits all over the place. 
 at another place where I saw this when certain loads were energized their 
circuit would go down to 75-80v and the other side would go up to 160v, not 
good for lots of stuff on either circuit!

and yes, this can make the neutral be not so neutral, your tower may be the 
return path for substantial current if this happens under certain 
circumstances, DO NOT disconnect or connect anything that goes to the tower, 
you may find that a simple coax is taking the unbalanced current to ground that 
way and disconnecting it could result in high voltages between the coax and 
radio while you are holding it!


Jan 25, 2016 07:59:59 AM, kzerocx@rap.midco.net wrote:

“I?m not certain the AC in my house is up to specs.......I have a couple of 
branch circuits constantly blowing incandescent bulbs, not sure why, last year 
our prelit Christmas tree (on one of those circuits) blew every bulb, one 
string at a time....WW3S"

It sounds like you have a missing, or poor, neutral connection. If you measure 
the problem branch circuits, is the voltage high?

I was also about to suggest disconnecting EVERY conductor to the tower to see 
if the RFI abates. You may have something connected from the house to the tower 
that is energized all the time, such as neutral current, mentioned in the 
previous sentence, flowing on a coax shield.

A tower will re-radiate RFI. Years ago, a friend had terrible broadcast band 
mixes all over 160 and 80 meters. I DFed the mixes with a broadcast field 
intensity meter...a Potomac Instruments FIM-41. Everything was coming from my 
friend’s tower. It turns out that he had an old run of Heliax going up to a 
remote coax switch about 50 feet above ground level. The Heliax was unjacketed. 
The poor contact between the tarnished copper outer conductor wrap-locked to 
the galvanized zinc coating on the Rohn 25 was behaving like a large number of 
detector diodes. Once the Heliax was replaced with jacketed cable, the mixes 
were gone.

Gary
k - zero - cx
Rapid City, SD 
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