For driving NTP.. 1) NTP works in microseconds and your networked clients will see accuracy in the range of a few milliseconds.
2) There is a way to fix this in NTP's configuration file, you can specify what the delay is. On Tue, Jun 9, 2015 at 9:30 PM, Ed Armstrong <eds_equipm...@verizon.net> wrote: > Hi, this is my first post ever to a mailing list, so if I'm doing anything > wrong please be gentle with your corrections :-) > > A short time ago I purchased a Nortel/Trimble NTGS50AA GPSTM, I'm sure > many on this list are familiar with it. At the time of purchase, my only > interest was the 10 MHz output, for use with my HP5328b frequency counter > and perhaps in the future also my signal generator. No question here, it > just works great as is. However, it certainly seems best to leave these > devices powered up all the time. > > OK, now were getting close to my question. The unit pulls about 10-11 > watts, which is really not very much. But it kinda bugs me to have it sit > there using electric and basically doing nothing when I'm not using it. So, > I bought a Raspberry Pi 2 with the intent of using it as an NTP server. I > can't really say I'm enjoying my intro to Linux a whole lot, but I'll get > there. It still needs some work, but it does function with the PPS output > from an Adafruit ultimate GPS, which I bought for testing this and possibly > building my own GPSDO in the future. > > The NTGS50AA is a very capable device, but unfortunately it does not have > a PPS output. Instead it has an even second output, which goes low for > approximately 50 ns. The falling edge of this pulse marks the beginning of > the second. During my search for a solution to this, I came across a post > from this mailing list which I believe was discussing repair of one of > these units. Someone in that post mentioned that there was a PPS signal at > test point 33 which went low for about 10 µs. Thank you, that saves me a > lot of probing. > > The first thing I did was verify that this pulse did exist, then I decided > to examine it a little closer. I kind of suspected that it may have been a > rather raw pulse as received from the satellites. I found out that is not > correct, once the unit successfully phase locks, this PPS signal is very > accurately tied to the 10 MHz output, even when the unit goes into holdover > mode. I was very happy about this :-) Next step was to see how accurately > it was synced to the even second pulse. The bad news is that it does not > occur at exactly the same time as the even second. The good news is that > the offset is very consistent, 253 ns before the even second pulse, +/- 1 > ns. > > My next step was to find out where the even second pulse entered the > output circuitry. I then broke the trace taking the even second into the > output circuitry, and ran a piece of 30gauge wire wrapping wire from the > via at test point 33 to the via at the input to the output circuitry. The > wire fit so perfectly it felt like the vias were made for just this purpose > :-) Now I've got a very nice PPS signal available both at the front jack > and at the backplane connector in the rear of the unit. > > OK, here is the actual question. Do you think it is OK to consider a pulse > which arise 250 ns early to be close enough? And no, I am not forgetting > about that 3 ns, there is about 3 ns of delay added by the output circuitry. > > Hope you didn't mind the long-winded post, and I thank you in advance for > any advice you offer. > > > Ed > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.