[time-nuts] Rb source looking good Rb-wise

[ed breya]

Just thought I'd report a little on my portable Rb reference source. 
This has been shut down for a few years, due to a failure during some 
experiments. I couldn't recall what the problem was, and now I remember 
after running it recently. A little over a week ago, while doing some 
other experiments, I happened to walk past it, and decided to flip it on 
to see what the deal was. I kind of forgot about it, and the next day or 
so, I noticed the Rb lock light was on, so that part seemed OK. I 
quickly found that the several 10 MHz outputs - all of them - were dead, 
so couldn't measure any result. However, the 100 MHz, 1 GHz, and 10 GHz 
outs all worked, so the basic guts were OK, and the 10 MHz were out, due 
to some local failure. That's way better than the whole thing being 
crapped out. I remembered that the 100 MHz PLL is really the heart of 
it, referenced to the Rb's 5 MHz, and the 10 MHz is derived from the 
feedback divider. So, yet another project to figure out and fix.

The Rb was looking pretty good, having a day or so warm-up head start 
before I noticed and started looking at it. The 10 GHz shown on the 
HP5350 counter was about 4-5 mHz low (indicated by -5 Hz by the 1000X 
factor). A little gradual tweaking of the Rb brought it to all zeroes 
after a while. In normal mode it showed about +/- 2-3 mHz excursions 
peak, and in "smooth" (averaging - don't know what the routine is in 
this counter) it presents typical +/- one count around the all zeroes. 
That's my present limit of resolution, until some other projects are 
completed. It has been running steadily since, still looking good. I 
think the last time I tweaked it was probably those years ago, against 
the Z3801A, using the same method.

Ed