Rick Putz asked To All, Has anyone done any studies on the Nav Man Jupiter T and Pico T series receiver s? They use the SiRF chip set and provide a 10 Khz output that is said to be co herent with the 1PPS. Just curious.
I did a lot of testing on the Jupiter-T that has an ONCORE VP physical footprint and MOT compatible command set. First of all, it is NOT the SiRF chipset. As I understand it, Collins/Rockwell sold their semiconductor operation lock, stock & silicon to the C/R spinoff Connexant, and it was Connexant that built the Jupiter-T with C/R parts and knowledge. Then Connexant's GPS was sold to SiRF, except that the Jupiter C/R series was sold to NavMan in New Zealand. So, under the assumption that the Jupiter-T you mention is the ONCORE footprint that I tested, here are a few answers. As a GPS receiver, the Jupiter-T is quite good, and better in fact than the old ONCORE VP. It is a 12 channel unit (ONCORE=8) so it can track more satellites and seemed to me to have better RF sensitivity. The Jupiter-T 1PPS timing is derived from a ~40 MHz clock, so that the sawtooth is only 25 pk-to-pk nsec in amplitude (ONCORE=9.5 MHz with 104 nsec pk-to-pk). The 10kPPS is coherent with the 1PPS and has the same 25 nsec pk-to-pk sawtooth jitter. Both of these differences were reduced in the more modern M12+. However, the Jupiter-T lacks the serial data output that tells the sawtooth error on the next pulse (ONCORE has message with +/- 127 nsec in 1 nsec steps). As I understand it, the MOT's generate 1PPS via a looonnnggg (> 1 second) counter that counts the rcvr clock and the quantization error can be reported. The Jupiter-T generates its 1 & 10k PPS thru an NCO, and the starting phase is not stored in the receiver; for this reason they never tried to reconstruct the error. I built a 10 MHz locker using the Jupiter-T and TvB's PIC-based synchronous counter with the idea that the 10 kHz jitter could be averaged out. The only problem came when the Jupiter-T went thru one of its clock zero-beat times (TvB calls them "hanging bridges") when the oscillator being locked got pulled off frequency. Alas, I abandoned that project! 73, Tom _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
