[time-nuts] 1pps signal presence with no GPS signal.
billj at ieee.org
Sat Jul 9 00:37:27 EDT 2005
David Kirkby wrote:
> Magnus Danielson wrote:
>>> In my case, I intend locking two items to 1pps.
>>> a) PRS10 rubidium from Stanford.
>>> b) HP 10811A via the Bruce Shera board.
>> I assume you mean the Brook Shera board from A & A Engineering:
> Yes, sorry, I meant Brook and not Bruce.
>>> As far as I can tell, the PRS10 will not update the rubidium's
>>> frequency unless the 1pps is present, so it would seem to me the
>>> PRS10 would benefit from no 1pps signal rather than the wrong one.
>>> But perhaps I am wrong.
>> I think you are right. As I recall it, it stops learning from lack of
>> As always, stop assuming and know instead.
> I'm pretty sure that is correct, but will double-check the Stanford
> manual. But that was how I understood it.
>>> In the case of a 10811A via the Shera board, I am less sure.
>> I scanned the article,
> There's a pdf on the web by the way.
>> but no real clue. However, if it is missing, it should
>> be a small feat to fix the PIC code to do it properly.
> Although I will have to double check, I believe with no pps input, the
> DAC voltage remains fixed, so the voltage applied to the EFC input on
> the 10811A will be fixed.
>> Basically, lack of PPS
>> within say 1.5 sec of the last one means go into hold-over state.
> Incedentely, when I changed the register value on the M12+ timing
> receiver to stop the 1pps output if there is no lock, it still
> produces it for about 5 seconds after the antenna is disconnected. But
> given the time constants used in the control loops are likely to be
> hours, a few seconds will have no significant effect I would guess
> (although I have not sat and worked it out carefully).
>> When in
>> hold-over state just keep the same DAC value. If you are fancy, you
>> do more
>> (the HP SmartClock technology is neat since it will actively
>> compensate for
>> perturbations in environmental variables etc to predict the trimming
>> which is cool).
> Em, that is being clever. I think I'll just stick to removing the 1pps
> output if there is no lock. I've not read much about TRAIM, but I
> assume that is better than relying on locking to at least one
> satellite, since it will exclude any that are significantly different
> from the others. Although the Motorola manual suggests the reliability
> is such that a false error will occur once every 5.6 days (or some
> number similar to that), which hardly sounded too good to me. I need
> to understand a bit more about this.
> A couple of suggestions on how I think the Synergy SynPaQ III could be
> improved, if people choose to mount it inside another enclosure.
> 1) Allow some decent method of securing the unit inside another box.
> I have no doubt voided my warranty by drilling and tapping the case
> with a couple of M3 threads, so it can be secured from underneath. It
> seemed better than making up brackets, or cable ties.
> 2) Have some method of bringing the drive to the LEDs out of the box,
> so they can be replaced by LEDs on a front panel. I'd like to get the
> 1pps LED to a front panel, but short of soldering wires onto the PCB,
> that is not possible. I might either use a light pipe, or use the 1pps
> output and put it into a pulse stretcher, so it can drive an LED on a
> front panel. I'm not sure of the speed of a 555 timer, but I suspect
> that will do the job of stretching the pulse to something that is
> reasonable for an LED. But it would make life a lot easier if those 4
> LEDs could be bought onto a front panel with not too much hassle.
> David Kirkby
Well you could use some sleeving to attach photo transistors on the
existing LED's and use
that to drive your front panel LED's. Kinda haywire but you don't have
to modify a board.
Think of it as a electronic light pipe.
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