Chris wrote:
What is the current requirement for the 10811 EFC +/- 5Vdc ? Is there any advantage to having it served by batteries?
Only the leakage current in the varactor, which is why Rick suggested operating with Vefc at the high end of the range. But even a mercury cell is not stable enough to do this job without electonic regulation, so you pretty much need to suffer with regulator noise even if you use a battery. In any case, there is a limit to how quiet it pays to make the EFC supply, because, as Rick also pointed out, the other end of the varactor is connected to an internal reference that is not the quietest voltage source in the world, filtered with a corner frequency of around 3 Hz. By referencing to this voltage rather than ground, as Rick suggested, you could reduce noise modulation (but it requires bringing the reference voltage out, which HP did not do).
I'm not sure how much practical difference this would make, compared to the inherent phase noise of the crystal. The 10811 normally runs with the EFC pin grounded (6.4 V across the varactor, referenced to ground at the anode). I suppose the best thing to do is remove the varactor entirely and replace the trim cap with one that has greater mechanical resolution, though I imagine finding a part that has at least 10x better mechanical resolution and is no worse than the existing trimmer in terms of mechanical and thermal drift may not be a trivial task.
Best regards, Charles _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
