Agreed. The TBolt is the best. On Sun, Apr 1, 2012 at 9:10 PM, <[email protected]> wrote:
> The need for sawtooth correction comes from the fact that standalone GPS > receivers use a standard clock oscillator that is basically fixed frequency > (save for temperature and other fluctuations) and their only option is to > align the desired PPS to the closest clock pulse. > > Please note that the Thunderbolt does not need sawtooth correction because > it uses the OCXO as its clock, and the GPS sofware can adjust its frequency > of course. It is a very elegant and effective solution that was available > to them because they were building an integrated GPSDO from the outset, so > not only they avoided the problem altogether, but they also saved an > oscillator in the process. > > It seems to me that if standalone GPS timing receivers used a VCXO instead > of a fixed frequency clock, the cost delta would not be that significant, > and they too could avoid the need for sawtooth correction. > > Didier KO4BB > > Sent from my BlackBerry Wireless thingy while I do other things... > > -----Original Message----- > From: Hal Murray <[email protected]> > Sender: [email protected] > Date: Sat, 31 Mar 2012 14:44:26 > To: Discussion of precise time and frequency measurement< > [email protected]> > Reply-To: Discussion of precise time and frequency measurement > <[email protected]> > Subject: Re: [time-nuts] 1 pps correction > > > [email protected] said: > > I’ve seen that the peak to peak jitter is reduced from something like > 27 ns > > to < 10 ns. > > > Is this a reduction of just the jitter, or is the actual accuracy to UTC > > also improved by this amount. > > Have you read the hanging-bridges paper? > Tom Clark and Rick Hambly: Timing for VLBI > http://gpstime.com/files/tow-time2009.pdf > I think that is the key to understanding this area. > > If you could average over many sawtooth cycles, you should get an accurate > answer. > > The problem is that you don't get to pick how many cycles fit into your > averaging time. The sawtooth pattern is the beat between two frequencies. > One of them is drifting with time/temperature. If you are unlucky, the > beat > frequency can be very very low. > > The sawtooth correction lets you correct on a cycle-by-cycle basis. You > don't need to average over many samples. > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > > _______________________________________________ > 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.
