It was a standard ground loop. This sort of problem can appear any time something is grounded in more than one place. The usual fix is to break the ground in one of them. 73 Stan, N3HS -----Original Message----- From: writelog-bounces at contesting.com [mailto:writelog-bounces at contesting.com] On Behalf Of Garry Shapiro Sent: Monday, February 03, 2003 2:27 AM To: writelog at contesting.com Subject: RE: [WriteLog] Hooking Isolation Transformer? Stan: Sounds like your hum was differential mode--i.e.on the audio--and the low-end rolloff of the isolation transformers took it out. What I am experiencing appears to be due to the transformers themselves by magnetic coupling. Garry, NI6T > -----Original Message----- > From: writelog-bounces at contesting.com > [mailto:writelog-bounces at contesting.com]On Behalf Of Stan Staten > Sent: Sunday, February 02, 2003 14:41 > To: 'Wayne Alexander'; writelog at contesting.com > Subject: RE: [WriteLog] Hooking Isolation Transformer? >>> I used two Radio Shack audio isolation transformers in a small > project box that I inserted in the middle of a standard stereo > patch cable. Got rid of the hum that I saw on the RTTY screen. > I had seen a spike every 180 cycles. Now the display is clean. >> 73 Stan, N3HS >>> _______________________________________________ WriteLog mailing list WriteLog at contesting.com http://lists.contesting.com/mailman/listinfo/writelog