li...@rtty.us said: > A number of them are sigma delta PLL's and have some really nasty jitter and > spur issues. Anything that shows up listed as "user programmable" - watch > out.
But "user programmable" won't find all the nasty ones. I haven't been looking recently. There used to be some that were field programable. The idea was that the distributor would do it so you didn't have to wait for the factory to grind the crystal to order if you wanted an oddball frequency. They didn't mention the PLL in the data sheet. You had to read between the lines. I assume the distributor stocked a handful of basic frequencies and there was a PC that told them which one to use and did the programming if you told it what frequency you wanted. It looks like a fun math problem. How many frequencies do you need to stock in order to cover a given frequency range with a given PLL chip? The result doesn't have to be a direct hit. You can include some fudge as part of the overall accuracy spec. (If you claim 100 PPM, but cut the crystal within 50 PPM, then you have 50 PPM left for the PLL.) -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.