Topband: Rotator creating spur on 1820

[K4SAV]

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