Thanks for all the links, info and comments guys!
>>Hi >> >>Several of the "big guys" have tried this approach. >> >>The problem seems to be that you are at the mercy of the guy who is >>transmitting the signal. He may (or may not) be very good at keeping things >>running right. Regulations may (or may not) actually require him to lock his >>signal to GPS. >> >>A lot of these systems work just fine at> 1.0 x 10^-8 off frequency. You >>have to keep the slots lined up between them, but as long as everybody >>agrees on alignment, they keep running fine. There's a lot that you can get >>away with and still be providing a dial tone. > >GSM and hence UMTS has 50 ppb requirements in the base station frequency. For >GSM no timing is required, but synchronisation of several base-stations has >been shown to improve hand-over performance. >Depending on the operator you tune in to, it may or may not be locked to GPS >or similar... but may also run from caesium beams somewhere completely >different, if so you are only guaranteed 1E-11 in frequency long-term. > >There is many systems, and you also need to tune in to the right signal. GSM >for instance may frequency jump regularly. > >Digital TV signals may be also be used. Depending on which mode the network >operate in the transmitters may be undisciplined or locked to GPS directly or >indirectly. DVB-T for instance has regular pilot-tones in the spectrum. A >DVB-T receiver is a nice exercise... :) > >It's possible, but not trivial. > >Cheers, >Magnus > -- Raj, VU2ZAP Bangalore, India. _______________________________________________ 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.
