Andrew Holme wrote:

My PR155 has 50 Hz phase modulation sidebands on the interpolating VFO, when
operating from AC mains. It's clean running from external DC, but the
sidebands return if the mains transformer primary is energised with the
secondary open-circuited. Could it be the magnetic field? Has anyone else
noticed this?

Bad supply caps leaving residual 50 Hz on the VFO supply lines. Get out a
meter and I bet you'll see AC noise there.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."