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-boun...@contesting.com] On Behalf Of donov...@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" <radi...@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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband