Topband: Topband crud
rees.a at btconnect.com
Thu Dec 29 07:47:09 EST 2005
I had a similar problem, a few years ago, with two monitors. I changed the monitors for a Compaq S710 and HP Ultra VGA 1028 , both 17 Inch. Noise and crud completely disappeared, only to re-appear every 60KHz with a 3COM Switch and Router when I put my Shack network in.
Changing the Switch for a cheap Belcom / Linksys Switch Router combination cured the problem. still using traditional CAT5e Cable though. All nice and quiet now.
Adrian Rees (M1LCR)
From: topband-bounces at contesting.com on behalf of Garry Shapiro
Sent: Thu 29/12/2005 08:39
To: Topband Reflector
Subject: Topband: Topband crud
OK, topbanders--here's a crud problem I could use some help with.
I noted that a segment between roughly 1815 and 1822 contained a steady
carrier at 1818.09 and discrete sidebands either side, spaced 85 Hz, clearly
visible on a Spectran display. Further, this was only manifested when
listening on my Beverages but with no directional differentiation, and the
signals were virtually undiscernible when listening on the TX antenna,
essentially a bent dipole at 130 feet or so radiating mostly up and away
from the station. This suggested that the source was very local.
I then recalled that 85 Hz was mymonitor's vertical refresh rate.
I use a ViewSonic 19" CRT monitor in XGA 85 mode. When I lowered the
vertical refresh rate to 75 Hz, the unwanted crud moved up about 20 kHz, and
the sideband spacing became 75 Hz. OK, mystery solved--but the question
remains: how to solve this so that I don't have to choose what part of 160
to have screwed up.
I presume the monitor electronics are directly radiating into the radio.
Before I start the usual brute force appraoches--ferrites, cable re-routing,
etc, do any of you have some mitigation ideas?
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