Hello Ed, Wow - what a great reply and thanks for your analysis. I am cc'ing the HPSDR discussion group in this reply.
Well, I think the answer I am seeing for what we are trying to accomplish is 'good enough'. One of my friends that I consider to be one of the best engineers that I have worked with says, 'good enough is perfect'. 73's, John AJ6BC On Sat, Apr 14, 2012 at 10:18 PM, Ed Palmer <[email protected]> wrote: > I recently had a chance to look at the GPSTCXO. I was quite impressed. > It's performance is a lot better than any bare GPS receiver, but maybe not > as good as some GPSDOs. > > Here are some measurements that I made on the 1 PPS of the GPSTCXO and > other GPSDOs: > > GPSTCXO .... Std. Dev. < 400 ps. min-max range < 4 ns. > Tbolt ................ < 500 ps. ............. ~ 4 ns. > Z3801A ............... < 300 ps. ............. ~ 2 ns. > Z3817A ............... < 100 ps. ............. < 1 ns. > > These measurements were 1000 pulses or more measured with an HP 5372A or > 5370B for the Z3817A. The Z3817A requires an external 1 PPS source to lock > to. I used a Navsync CW12-wi. Over longer periods of time typical GPS > wander is present in all units. > > I measured the 10 MHz output of the GPSTCXO with the Histogram Time > Interval function of my 5372A. Out of 200 million cycles, every one had a > period of either 100.0 or 100.2 ns. There wasn't even one outlier. I have > OCXOs that aren't nearly that good. > > A few random points to remember about the GPSTCXO: > - There's no way to set the time zone offset - fixed at UTC. > - There's no way to set the elevation mask - fixed at 10 degrees. > - The Allen Deviation matched the graph in the manual which is available > at the Jackson Labs site. > - On the evaluation board, the 1 PPS is wired to the "DCD lead" on the > USB-emulated serial port. > - I can confirm that, as mentioned in the manual, performance improves > substantially when you shield the unit from temperature fluctuations. > - If you use Z38XX to communicate with the GPSTCXO be sure to disable > serial echo as described in the manual. The GPSTCXO _really_ doesn't like > serial echo. It can cause the unit to reboot. > > The GPSTCXO stands between a bare GPS timing receiver and a typical GPSDO. > It's performance is closer to a GPSDO than to a GPS receiver, but it's > price is closer to the bare receiver than to the price of a new GPSDO. It > should be useful in many situations. > > I have no relationship to Jackson Labs. They did make a GPSTCXO available > to me for this testing. > > Ed > > > > On 4/14/2012 7:10 PM, John Westmoreland wrote: > >> Hello Fellow Time-Nuts, >> >> I am new to the group - and was asked by someone from HPSDR/TAPR to get an >> opinion, good/bad, of the attached PDF which I hope doesn't exceed the >> allowable byte size of posts. >> >> Jackson Labs has given me a verbal on the attached as sub $300.00 QTY 1. >> We are seeing if there is interest in a possible 'bulk' buy. >> >> I will post more on the HPSDR Wiki as soon as I sort out my password - and >> will post an e-mail regarding the other files associated with the GPSTCXO. >> >> If there is sufficient interest we may do a spin of the HPSDR Excalibur >> project or perhaps just do a new project with the attached device. It >> should be easy to interface >> directly to the Alex Bus in the OpenHPSDR Architecture. >> >> Thanks and 73's, >> John W. >> San Jose, CA >> AJ6BC (Ham Call Sign) >> >> > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<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.
