Thread: Plessey PR155
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Old July 4th 05, 02:21 PM
Scott Dorsey
 
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Andrew Holme wrote:
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.


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.


WHOA! That sounds like magnetic leakage, yeah.

Another possibility might be AC leakage to chassis through a filter
in front of the power transformer.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."