I wrote:
> (Note that a 256 cycles per second error is 51 PPM at 5 MHz.)
> In the real world, you should be able to trust that any oscillator that is > chosen for a GPSDO will free-run within 1 PPM when it is warmed up, and > that your PPS will always be within 1 PPM, as well.
Hal wrote:
Why? The original goal was low cost. I could easily believe that an inexpensive oscillator would be off by more than 1 PPM.
Decent OCXOs are falling off the ebay tree for $20 every day (less, if you look and wait -- I've bought several for <$5). I have bought dozens of them, and have yet to receive one that isn't within 2e-7. So I'm inclined to think any oscillator that is worth using for a GPSDO has a very good chance of being within 1ppm without any adjustment or selection. Further, there are good ways to get an oscillator within 1e-6 without a counter -- for example, beating with WWV.
Indeed, if cost is the limiting factor, I submit that most people would be better served by spending their entire budget on the best OCXO they can buy and a box to put it in to reduce temperature fluctuations, then manually calibrating it periodically, than by buying a cheap oscillator and spending money on a GPS, uC, etc. in an attempt to make a silk purse out of it. GPS can only help at long tau (or said differently, it can only help at short tau if the oscillator is too unstable to be worth using in the first place).
Best regards, Charles _______________________________________________ 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.
