Some years ago I received a complaint from W4ZV about spurious signals offset about 1 kHz or so on my Icom 751A. There was no amplitude modulation of the carrier visible on scope, yet Bill could easily hear the spurs.
It turned out the toroidal transformer in the 751A internal power supply had enough flux leakage to change the reactance of the VCO coils that were about 3 inches from the toroid. The rig was being FM modulated. I rotated the power supply 90 or 180 degrees and the problem went away. At radio frequencies using a red "-2" mix, there can be almost 30% change in inductance from spreading or bunching turns in a coil. This is from core flux leakage. I've had low pass filters put ripples in an adjacent filter when the toroids get too close. These cores are largely touted as "self-shielding" in our handbooks. I'd be very careful accepting broad general statements without looking at the specific case in question. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
