[time-nuts] The VE2ZAZ GPSDO

Randy Warner Randy at synergy-gps.com
Sat Oct 21 16:35:44 EDT 2006

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

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 ;-)


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of SAIDJACK at aol.com
Sent: Friday, October 20, 2006 11:30 PM
To: time-nuts at febo.com
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...

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