Hi Jerry
Any cable/wire is an antenna. If it long enough or near 120ft it will work
like a 1/4 wave vertical. The path to the ground is important because the
current will add to other circuits at the input of the receiver. Even the AC
line can be the return path to ground.
You can watch the movie bellow and you can see the same problem at N8PR
station and how Pete fixed the common mode noise problem with few chokes..
https://www.youtube.com/watch?v=-4os4qcaT08
Interesting that disconnecting the rotor box from the AC line stops the
noise.
Some BC IMD can be generated by oxidation on towers or external metal
structures as well.
73's
JC
N4IS
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of
donovanf@starpower.net
Sent: Thursday, November 02, 2017 10:47 AM
To: topband@contesting.com
Subject: Re: Topband: Rotator creating spur on 1820
Hi Jerry,
There's a good chance the problem originates inyour control box rather than
your rotator. Does the problem stop if you completely disconnect the control
box?
73
Frank
W3LPL
----- Original Message -----
From: "K4SAV" <RadioXX@charter.net>
To: topband@contesting.com
Sent: Thursday, November 2, 2017 2:40:49 PM
Subject: Topband: Rotator creating spur on 1820
I have a problem for which someone on this forum has the solution. I know
that because I have seen that message sometime in the past.
The problem is that my rotator is rectifying a couple of AM station signals
and creating a spur on 1820. It's normally pretty weak on my receiving
antennas but sometimes it's a problem. I found that if I listen on my XM-240
near that rotator it can be very loud. As soon as I move the rotator it
causes the spur to go away, or become weak. A few minutes later it is back
again. It pops in and out.
So who had the problem and how did you fix it?
Note that my XM-240 actually shows a low SWR on 160. That's because the
XM-240 balun doesn't work well on 160 and the common mode currents on the
feedline couple to the tower and the tower becomes the real antenna on 160.
So in this case the tower is the antenna and it has that rotator cable
against it picking up max signal from that cable (also radiating it to my
other antennas). No, the XM-240 is not used on 160 (except to find the
source of this problem).
The rotator is a Yaesu G-2800DXA.
Jerry, K4SAV
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