I have a design based on the Motorola MT12+ receiver that uses a CMOS XOR-based PLL. I will send you the file with write up and schematic. Bob Q. ----- Original Message ----- From: "WarrenS Email" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, November 23, 2008 2:18 PM Subject: [time-nuts] GPSDO using 100Hz
> This is my first listing so don't know if I'm doing correctly. > > Question is: Has anyone done any work using the 100Hz GPS output, instead > of the 1 Hz output? > The reason I ask is because I am in the process of cleaning up my SIMPLE > GPS Freq Phase lock tracker breadboard that does about the same as most, > but in a different way. By using just a few basic standard 74HCxx IC > logic gates and Flip-Flops with RC's I phase lock a low accuracy VCXO to > give me a high accuracy 10MHz reference. This is something I built for my > own use, to check the accuracy of my 10 MHz freq standard and to check the > accuracy of the 60KHz WWVB signal. > > I found out that the most important trick to keep the GPS tracker simple > (GPSDO), fast and low power, and do it without the usual microprocessor > stuff, was to use the 100Hz output instead of the 1HZ output from the > Motorola Oncore receiver board. Basically this allows simple logic > circuits to give 10 to 100 times better results, such as phase noise of > around 1 ns instead of 100ns from second to second, cold turn on and full > accuracy lock of the tracking osc in well under a minute (with GPS left > on). It also has the ability to track the GPS phase errors at about a 10 > Hz rate which gave me some new interesting insight, such as the 1 sec > sawtooth error that the Oncore reports on, that would usually requires the > use of a computer to process, is no longer very relevant. > I found out the 1 second reported phase error is just an alising artifact > of a higher freq phase dither that can be completely filtered out with a 1 > second Time constant RC. (i.e RC replaces microprocessor). > > It generally takes about an hour Tracking time constant to get good 1e-10 > Freq stability using the 1 Second GPS signal, and more like 3 to 24 hours > as not degrade a really good Oscillator. > I am getting such good results with the simple high speed RC PLL, I am now > doing some test to see if there are new ways to reduce the Tracking time. > It would seem it should be possible to get 1e-10 in more like a 100 > seconds instead of an hour. This would then reduce the required stability > of the tracking Oscillator by an order of magnitude or better. The simple > PLL tracks the 100Hz within about 1 ns and can lock up in 10 seconds, and > the GPS signals themselves don't seem to vary by more than about 10 ns > with 10 minute and 1Hr average times. (from > http://tf.nist.gov/service/gpstrace.htm) > I have not found any GPS signal accuracy data for shorter average times, > so that is what I'm presently plotting. > One of the other many benefits of fast GPS tracking may be the possibility > of a more mobile Disciplined Oscillator. > > If anyone has done any work using the 100Hz Oncore GS signal to do > frequency tracking, I would be very interested in further discussions. > > Warren > ******** > _______________________________________________ > 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. _______________________________________________ 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.
