Topband: Rotator creating spur on 1820

K9RT at K9RT at
Thu Nov 2 12:41:27 EDT 2017

Interesting you have the spur on 1820.
I have the exact same situation on 1820 as well. Sometimes I can actually  
pull weak audio off the spur but have not been able to identify which local  
station or stations are mixing to create the spur.
It never varies in strength and I just assumed it was part of the hazards  
of operating on topband. Didn't consider it might be the rotor and or cable  
going up the tower. In my situation it hasn't caused enough interference to 
 detract form DXing so far in at lest 20 years +.
Good information to have for those closer  to AM broadcast towers in  the 
Dick K9RT
In a message dated 11/2/2017 10:41:52 A.M. Eastern Daylight Time,  
RadioXX at writes:

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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