Thread: Plessey PR155
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Old July 3rd 05, 04:08 PM
Andrew Holme
 
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Scott Dorsey wrote:
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


Clarification:
There is no ripple on the supply when the set is powered from DC, but I
still get sidebands if I apply AC mains to the transformer primary with the
secondary temporarily disconnected.