Hi Graham, its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. This causes huge cycle-to-cycle phase jumps. One cycle maybe 100ns long, and the next adjacent cycle could only be 87ns long! Without filtering, I doubt the output is useful for much because it has phase jumps from cycle to cycle of 10's of nanoseconds or more. A true GPSDO (even the cheapest one) has cycle to cycle phase "jumps" of femtoseconds only due to oscillator jitter. You can easily make a GPSDO out of it though through a simple EXOR gate (74AC86), feeding a TCXO/VCXO through a low-pass filter, and designing a phase loop low-pass filter with less than say 10Hz bandwidth.. That approach has been discussed here in the past a couple of times and is very cost-effective. That is essentially what the Conner Winfield units do. The drawback is that you have very large phase and frequency jumps when going into and coming out of holdover on these units, because the unit does not have a holdover oscillator with any type of reasonable stability, and whatever high ADEV stability your filter oscillator has is lost due to the analog loop bandwidth of typically >10Hz meaning the internal $1 crystal of the GPS receiver itself determines ADEV. Bye, Said In a message dated 8/19/2014 10:03:27 Pacific Daylight Time, [email protected] writes:
Said, Agreed, hence my reference as "a very simple self-contained GPSDO". Even after a very quick first glance at the documentation it didn't seem like it would be much of threat to more traditional GPSDO's. It will be interesting to play around with and see what it can do. Cheers, Graham ve3gtc -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Said Jackson Sent: August-19-14 12:44 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ublox neo-7M GPS Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (>>10s).. Sent From iPhone > On Aug 19, 2014, at 9:20, "Collins, Graham" <[email protected]> wrote: > > Good day all, > > On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). > > This seems all too good to be true. Sounds like a very simple self-contained GPSDO. > > I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. > > I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. > > There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. > > Cheers, Graham ve3gtc > > > This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. > > Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’ usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’ expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. > _______________________________________________ > 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. _______________________________________________ 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.
