[time-nuts] GPS W/10KHz
bob at evoria.net
Mon Feb 10 18:21:20 EST 2014
I was waiting for someone else to mention this. The problem with the sawtooth from a UT+ and similar is that it can go long periods with the phase on one side of zero, switch to going back and forth across zero, and then even start at one side, and do a sawtooth shaped stairstep ramp to the other side. So the phase of your oscillator is going to be pulled all over the place. Long term average is going to look good because it has to average to zero. But short term, the accuracy of your GPSDO may suffer.
OTOH, with one of the newer inexpensive receivers, the sawtooth is only about 10ns total. If your circuit is for frequency averaging, or for phase crossings, it can do pretty good. However, if you have a phase locking system, then there are quantization errors that are shaped a bit different from the UT+, but they still cause you a problem.
Bob - AE6RV
> From: ""Björn"" <bg at lysator.liu.se>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>Sent: Monday, February 10, 2014 4:37 PM
>Subject: Re: [time-nuts] GPS W/10KHz
>The sawtooth correction is the difference between where the receiver would
>wish to place the edge and where its known limited resolution electronics
>lets it put the edge.
>The receiver wish is based on the timesolution from the last measurement.
>In the Jupiter this is done at 1Hz maximum. The sawtooth correction will
>apply the same for all 10k (pos or neg) edges in the 10kHz signal during
>that one second.
>There are effects that are not easily filtered away in the analog domain.
>See the archives and
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