Hi Bruce, I wonder how the analog switches' tempco would affect the performance. They usually do have 10 - 100 Ohms series resistance if I remember correctly. The Temex OCXO is achieving STS of parts in E-013, it would be unfortunate to lose that performance due to external circuitry. At these extremely small values, I would guess that the finite off-resistance of the switch, and the leakage currents through the switches' transistors would also degrade the performance. Maybe a mechanical relay would work better? But that would cause a mechanical vibration that could jerk the crystal. Also, I guess one would have to add a small RS-232 micro to decode the Validity bit from the GPS and do the actual switchover. Here is an interesting factoid: Magnus mentioned that many GPS receivers do strange things when they go into holdover. I can only concur to that. The M12+ and M12M are really excellent in this, but other receivers are not and may give you a couple of 1PPS pulses that are way off, say 200ns or much more before they shut up. Not so nice. bye, Said In a message dated 2/13/2008 15:09:54 Pacific Standard Time, [EMAIL PROTECTED] writes:
It would also be necessary to use an analog switch in series with the PI filter input resistor and for extended holdover keep the PI filter feedback cap charged at the DAC voltage to minimise transients on reverting to normal operation. Bruce **************The year's hottest artists on the red carpet at the Grammy Awards. Go to AOL Music. (http://music.aol.com/grammys?NCID=aolcmp00300000002565) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
