I believe the Allan variance graph in Trimble's data sheet was taken before Selective Availability was turned off. I'm not sure what impact this would have; I wouldn't expect any at all at tau << 100s.
A pronounced hump in the ADEV plot could suggest that the disciplining loop is underdamped. Ideally you wouldn't be able to tell where the OCXO's influence ends and GPS's begins. -- john, KE5FX > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Behalf Of Mark Sims > Sent: Friday, July 11, 2008 2:51 PM > To: [email protected] > Subject: Re: [time-nuts] Allan variance of Thunderbolt > > > > The Thunderbolt data sheet says that the unit requires 25mA at > 12V. That spec would imply it is for a unit without an OCXO > since the oven heater draws considerable current from the 12V > power supply. But then, the data sheet says it draws 15 watts > cold, 10 watts steady state. That implies the unit has a heater. > And if you multiply the published power supply requirements out > you get 2 watts, not 10-15 watts. It appears that some of the > specs are for an ovenless unit, others are for the ovenized unit. > > The data sheet also talks about a telecom version with improved > holdover performance... this has got to be the ovenized unit. I > suspect the Allan variance plot is for the low end unit, but the > shape of the curve is funny. It always slopes downward. Almost > all GPSDO Allan variance plots show a hump in the graph around > 100 seconds. > > Trimble's numbers and graph shape do seem to relate closely to my > "auto-Allan variance" plots of the OSC offset data supplied by > the unit (where the tiiming reference is its own interpretation > of the GPS time signal). > _______________________________________________ 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.
