Hi The vast bulk of all GPSDO’s sold over the last three decades were sold because the first CDMA specification required that the basestation operate without a GPS signal for 24 hours. During that time the alignment of the Gold Codes is required to be within 10 us of “GPS time”. Once the codes go out of alignment, the cell phone takes an interference hit, so the the basestation must be shut down.
The time and code alignment requirement has “evolved” over time. Various 3G, 4G, 5G, 6G .. systems have tighter timing specs (or apparently none at all). Technology has also evolved. A self contained GPSDO located at each and every transmitter is no longer the only way to do this. We have 1588 and a number of other tools that didn’t exist in the 1980’s. Bob > On Dec 18, 2016, at 11:20 PM, Bob Stewart <b...@evoria.net> wrote: > > Hi Scott, > I do understand the reasons that these users want this quality of output. > It's who these users are, what fields, industries, etc, that I didn't quite > understand. > Bob ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Scott Stobbe <scott.j.sto...@gmail.com> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Sent: Sunday, December 18, 2016 8:22 PM > Subject: Re: [time-nuts] 1PPS users? > > Part of the reason 1PPS needs to be so clean is because you are continuously > integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty > trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane > AT-cut crystal subject environmental dynamics becomes ludicrous. More than > likely the short term stability of GPSDO is cleaner than it needs to be for > many applications, but that is so holdover over an hour or day remains > reasonable. > On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart <b...@evoria.net> wrote: > > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? > Bob - AE6RV > ----------------------------- ------------------------------ ------ > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > ______________________________ _________________ > 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. > > > > > > _______________________________________________ > 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. _______________________________________________ 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.
