The Eternal Squire wrote:
Now I have a wiper that is laid across the edge of the disk to make or
break contact with the outside of the star pattern, with 12 Volts DC
potential on the wiper. Assuming the shaft was conductive and made
firm contact with the center of the star pattern, should I see a 10
Mhz
square wave, suitable for say a switching mixer?

Question: How bad are the phase noise and harmonics likely to be?

Really bad, but the harmonics you can filter. Phase noise is going to
be way too high for anything but CW and your frequency stability won't
be anything to write home about. However, the system you describe was
built by Federal Electric in the 1920s, so it's at least practical.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."