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[Towertalk] re water pipe ground

To: <towertalk@contesting.com>
Subject: [Towertalk] re water pipe ground
From: ccc@space.mit.edu (Chuck Counselman)
Date: Tue, 31 Dec 2002 15:47:06 -0500
Really the best advice, as someone has already written in different 
words, is to use a balanced antenna with a balanced feedline, so that 
the net RF current flowing into the shack is zero.  It's fine to run 
an unbalanced transmission line such as coax into the shack if (1) 
your antenna is balanced; (2) the antenna does not couple to the 
feedline; (3) a good balun is used at the transition to the 
unbalanced (usually coaxial) line; and (4) since the first three 
conditions are never perfectly satisfied, the coax is loaded with 
common-mode RF chokes.

I do all four, and although my second-floor shack has no RF grounding 
(just safety grounding), I have no RF in the shack and my receiver 
hears no AC-line or other artificial noise.  Today at 2:30 AM while 
working a weak QRP station on 80 meters, I observed that even with my 
very sensitive (Icom IC-775DSP) transceiver's preamp switched in(!), 
my S-meter rested at zero between the usual noise bursts from distant 
lighting, and I could hear _no_ man-made noise.  My computer was 
running on the same table; it and three fluorescent lamps were 
plugged into the same AC power branch circuit as my transceiver; and 
in the room directly below me were three multi-hundred-watt 
incandescent lamps, each lit but dimmed by an ordinary Triac/SCR-type 
dimmer, a.k.a. QRO QRN generator.

Most of the AC-line buzz, digital-computer hash, etc., that most hams 
hear is conducted to their antennas from their houses by common-mode 
current on imperfectly balanced feedlines.  I heard it, too, before I 
learned to balance everything and eliminate the unbalanced, or 
"common" mode.

-Chuck, W1HIS


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