Topband: RFI On TopBand by 57JNDenneny

Dick Bingham dick.bingham at gmail.com
Tue Jul 23 17:36:18 EDT 2019


Regarding ===>
"Message: 1
Date: Mon, 22 Jul 2019 15:59:44 -0700
From: <57JNDenneny at comcast.net>
To: <topband at contesting.com>
Subject: Topband: RFI on TB "

As a starting point to check-out *everything* between the feed-line
connection directly at the *antenna feed-point*
and a receiver, connect a 50-ohm termination at the *antenna-end* of the
feed-line (assuming 50-ohm coax).
Is the "RFI"  gone and no detected signals, if so, good.

If *not,* you have bigger problems! Terminate the receiver (after removing
the antenna feed coax from the receiver)
in 50-ohms - record the S-Meter 'reading' .

Replace the 50-ohm load on the receiver with the feed-line and record what
the S-Meter is displaying - is it close to
what was recorded with the 50-ohm termination ? If not, you have some
serious clean-up work to do.

You will be dealing with Common Mode (CM) currents that have to be
eliminated. The "clean up" process is more
easily accomplished if you have a near-DC-to-30MHz spectrum analyzer
available to ensure you are not dealing with
10-pounds of 'stuff' in a 9-pound capacity flexible container - push it
down 'here' and something pops-up 'there'.

Once the CM-issues have been resolved, your receiver S-Meter will be,
almost certainly, close to S-zero in the absence
of desired signals and propagated noise. This is what I have been able to
achieve in a big city environment at CN97uj
using balanced dipoles and feed-point chokes.


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