Topband: Topband crud
garry at ni6t.com
Thu Dec 29 03:39:56 EST 2005
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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