[time-nuts] GPSDO using 100Hz
warrensjmail-one at yahoo.com
Mon Nov 24 11:49:49 UTC 2008
Thanks for the great Information.
>UR) James Miller, G3RUH, also uses the 100 Hz signal
Thanks, that is what I was asking for, other people that were using the 100Hz.
Now if I could just figure out how to post a response under an existing
thread, and not have it start a new one I'd be happy.
Concerning your other comments:
>UR) it's neither specifically new nor ...
I did not mean to imply that the 100Hz was new or its use was discovered by me,
Mostly I'm wondering why it is so little used, and I'm looking for other people using it.
Something that I can do with the 100Hz that you probable have not seen before is
the ability to make a GPSDO similar to Brooks Shera's processors based unit
using just 3 standard off the self 74HC IC's and a pretty crappy Osc.
>UR) The key error in your idea is the assumption that every 100 positive slopes of your
100 Hz is identical with the start of a new second, which is wrong when you look at it at
a second to second base.
Correct that my assumption was that every 100 pulses gives a one second pulse at the
same location.You are incorrect that when this is not true, it is a key error in my idea.
I did see that the 100Hz pulse that comes out at about the time as the 1Hz sawtooth
correction is updated seems to have the same amount of phase error as reported for
the 1 Hz, best I could tell. I do know it is sometimes true, I'll check that out better and
verify that it is not always true on my unit. Thanks for the information.
BUT, NO matter, because the max jitter error of around 100ns is the same in both of
the 100Hz and the 1 Hz signal, and the 100Hz error is nonaccumative.
That is when I average 100 points each with an uncertainty of 100ns I get at least the
Square root of 100 better resolution If they where truly random, which they are not,
they have the same basic ramp type phase response as the 1 Hz sawtooth, just much faster
so averaging works much better than if they where random.
What I have found is that the net effect is for the most part that averaging 100 100Hz
signals will give about the same error result as averaging 100 One second pulses.
If you want to proof it to yourself use a digital scope with an average function and look
at the results. (there are some rare exceptions, I skip over for now)
For another example, consider what the results would be if you just used every
100th 1 second pulse. You'd end up with 100ns uncertainty in 100 seconds rather
the under 10 ns you get by averaging 100 1 second pulses (most of the time).
UR) What is true is that the MEAN frequency of the 100 Hz is locked to the GPS
and that is why your fast PLL works as well as James Miller's.
What I tried to state is that the 100Hz is fast enough to make a simple analog PPL,
something that is not very easy to do with the 1 Hz signals.
Thanks for the name, I'll check more on how he is doing his simple GPS tracker.
It looks like he is using the 10KHz output of the Jupiter GPS.
Unfortunately my oncore does not have a 10KHz output.
James Miller, G3RUH, also uses the 100 Hz signal. So it's neither
specifically new nor the philosopher's stone that you may perhaps
believe to have found. The PPS and the 100 Hz signal come from the SAME
oscillator. The jitter in the PPS comes from the fact that the receiver
logic decides WHICH slope of the oscillator signal comes next close to
the TRUE point of time where the PPS should be generated. The key error
in your idea is the assumption that every 100 positive slopes of your
100 Hz is identical with the start of a new second, which is wrong when
you look at it at a second to second base. What is true is that the MEAN
frequency of the 100 Hz is locked to the GPS and that is why your fast
pll works as well as James Miller's.
More information about the time-nuts