Angus wrote:
I don't know whether the outputs on a Jupiter exhibit any granularity
or not (I've not seen anything to suggest that they do), but I think
that with receivers that do, changing from 1PPS to a faster PPS output
would normally change the granularity effects that are seen - assuming
things are not in sync.
As for possibly reducing the need for a fast clock; being able to
measure a number of pulses in a second and then take the average count
can allow a rather better resolution than just taking one measurement
- so in some circumstances this could be useful.
I've not really looked into it much, but was really just interrested
if anyone here had come accross the 100/1K/10K, etc pulses being used
like that.
Although that's not what I was talking about doing above, I think that
it's pretty much what some of the hardware GPSDO's actually do using
various types of oscillators (and to good effect too). As in these:
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm
http://www.frars.org.uk/cgi-bin/render.pl?parameter=&pageid=1285
the loop filter is basically just an RC circuit. It's not quite raw
GPS, but is quite different to using a digital filter as used in a
Thunderbolt, Shera, etc., which can run to hours.
When the N1JEZ board was mentioned, I assumed that it was this type of
controller that was meant - and I think it does need 10KHz unless it
gets much more of a mod than a couple of counters.
Angus.
Angus
The examples in the above links just illustrate how easy it is to fool
yourself if you don't use the appropriate measurement techniques to
measure the frequency stability of a GPSDO.
The 10kHz output is indeed phase modulated every second as indicated by
Figure 11 (attached) on the datasheet. To remain locked to the PPS
output as illustrated the 10KHz output must have the same timing jitter
exhibited by the PPS signal.
The fact you were unable to detect just means that your measurement
technique is inappropriate.
The phase modulation at 1Hz is somewhat pseudorandom.
Bruce
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