Steve, The suggestion of using the mains frequency as a reference is not practical. There will be no certainty, even after counting for a week that the mains frequency will give you a reliable reference. You said it yourself - "the instantaneous frequency of the mains is not always spot on".
The mains frequency specification is probably set down in a regulation somewhere, and it probably accounts only for a mean number of cycles per day, and so the counting period required to lock a reference would be too long. Essentially it is a reference with immense low frequency phase noise. Heaven knows, it's a challenge locking 10MHz to 1Hz, so locking to 1/86400Hz would be very difficult. An early mains frequency controller for power stations used a pair of synchronous clock motors (one on the mains, one driven by a crystal-controlled source), driving a differential gearbox which drove a pointer calibrated in 'seconds fast/slow', so potentially you could do the electronic equivalent, but I doubt that it would be capable of better performance than the OCXO on its own. If you want a cheap and cheerful 50Hz reference in NZ, use the frame frequency of TVNZ's TV1 or TV2 transmissions. They have a Trimble Thunderbolt GPSDO driving the sync generator. Just pull the sync out of an old video recorder. It's all been done before. Electronics Australia about 1976! 73, Murray ZL1BPU _______________________________________________ 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.
