Said et al, Although everything said in this thread is accurate, I guess I find myself a little reluctant to just trash the author and the project out of hand. He is obviously a hobbyist without a lot of precision timing theory in his back pocket (hey, I'll place myself in that category, I learn more everytime one of you guys posts to the list).
Does the project have problems and limitations? Absolutely. Will the 7805 and ripple counters create problems over temp? Certainly. Will they drift enough to cause problems for the author during use at fairly constant room temperatures in his HAM shack? Probably not enough to be noticeable. Does the project perform "well enough" for the author and other hobbyists that will enjoy building one for themselves? Absolutely. On the GPS side of things, we sell a LOT of nav receivers for timing applications. If you are designing a product that is cost sensitive and doesn't need ns accuracy or TRAIM functions of an M12M-T, a Sony GXB receiver will cost you about half as much and still hold the 1PPS within 50nS (1 sigma). Even though is is a nav receiver it's 1PPS performance is equal to the old UT+ timing receiver. Sorry for the rant. It's been a long week ;-) Randy ________________________________________________________________________ _________________________________ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Friday, October 20, 2006 11:30 PM To: [email protected] Subject: Re: [time-nuts] The VE2ZAZ GPSDO Hello Bruce, I agree. The DAC reference is an LM7805CT regulator with 0.8mV/C (typ.) temperature coefficient. Considering that typical Oscillators (MTI units for example) have about +-20Hz deviation per 5V - this alone - excluding the Opamps tempco, would lead to a temperature drift of 0.32Hz over a 50 Deg C temp range. That's about 3.2E-08, quite a bit worse than a good surplus oscillator. And the 7805 does not have a maximum tempco rating, so it could be 10x worse than that... bye, Said _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
