[time-nuts] Real-time Timestamp with Richard's PICTIC?

Tom Bales tob at starhouse.org
Fri Dec 26 16:18:40 UTC 2008


At 07:00 AM 12/26/2008, time-nuts-request at febo.com wrote:
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>Today's Topics:
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>    1. Re: Happy Holidays (Bruce Griffiths)
>    2. PPS from Samsung GCRU (Mark Stephens)
>    3. Re: Happy Holidays (Bruce Griffiths)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Fri, 26 Dec 2008 22:21:49 +1300
>From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>Subject: Re: [time-nuts] Happy Holidays
>To: mccorkle at ptialaska.net,     Discussion of precise time and frequency
>         measurement <time-nuts at febo.com>
>Message-ID: <4954A22D.10802 at xtra.co.nz>
>Content-Type: text/plain; charset=ISO-8859-1
>
Ho, Ho, Ho!  Thanks to Richard from the Cold North for such a nice 
Christmas present!

I've been working on a crackpot scheme to measure the time of arrival 
of cosmic-ray events.  It's a "crackpot scheme" because I want to 
record the times in a (no-doubt futile) attempt to see if any of the 
events are correlated in time--sent from a common source in a uniform 
pulse train, perhaps.

So for, I've assembled some simple detectors, an HP53131 interval 
counter, a Lucent RFTGm GPS/XO/Rb set for frequency reference, and a 
bunch of cables with the result that I can record the time interval 
between events to 0.1 nanoseconds, but not real arrival time.  I 
figured that I would just add up all the interval times to get a sort 
of real time, but after lots and lots of events, the cumulative error 
probably defeats the purpose (and missing events hurt your cause a 
lot).  So, I've been looking for a very precise, high-resolution 
real-time event timestamper.

This all started when I was listening to Tom van Baak talk about ADEV 
of pendulum clocks at the BHI anniversary symposium last summer, and 
how you could pick up the signature of astronomical events, such as 
lunar tides.  At the time I was reading a report about some 
physicists at Brookhaven discovering strange semi-annual rate 
variations in the radioactive decay of nuclei, and I was toting 
around a book about cosmic rays.  Funny how the brain works.  Oh, 
yes--and the LHC was starting up.  So, imagine some spaceman a long 
time ago in a galaxy far, far away firing up his proton accelerator, 
sending off pulses of protons into space, and a few of them hitting 
us here on earth every now and then.  It doesn't seem that anyone has 
ever looked for such a signal, so why not look for one?  (There are 
lots of complications, such as the motion of the earth, to deal 
with--but you get the idea.)

I haven't found a simple way to record a file of real-time time 
stamps, at least without lashing together a bunch of clocks, interval 
counters, GPIB controller, and so forth, but Richard's gift seems to 
have everything needed to do the job, except for a GPS time receiver 
to form the low-resolution part of the timestamp, and a software 
means of concatenating the data for date, hour, minute, and second to 
the high-resolution data from the PICTIC.  Can anyone offer suggestions?

Tom Bales
Coral Gables, FL



>Richard H McCorkle wrote:
> > Ho Ho Ho
> >
> > Merry Christmas from the far north to all the
> > Time-Nuts. As a gift for the holidays I have
> > created a free version of the PICTIC for you
> > and Didier has kindly posted the files at:
> >
> > http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic
> >
> >
> > And to all a good night,
> >
> > Richard
> >
> >
> >
>Richard
>
>Your analog interpolator needs a little work.
>The switching speed of the 2N3906's is so slow because the 2N3906's that
>switch the current to ground or into the 470pF cap are saturated.
>They will switch much faster if used as current mode switches.
>In fact you can just replace the 2N3906 whose collector is connected to
>the 470pF cap with a fast switching diode and the current source will be
>switched much faster.
>The 2N7000's have a relatively high non linear output capacitance
>replacing them with something like 1/6X 74HC05 would be better.
>The 470pF silver mica caps will have relatively large dielectric absorption.
>NP0/C0G caps would be a better choice, particularly if higher input
>pulse rates were to be used.
>
>Have you actually measured the linearity of the interpolator?
>
>
>Bruce
>
>
>
>
>------------------------------
>
>Message: 2
>Date: Fri, 26 Dec 2008 21:04:24 +1100
>From: "Mark Stephens" <marks at twotoe.com>
>Subject: [time-nuts] PPS from Samsung GCRU
>To: <time-nuts at febo.com>
>Message-ID: <C1483046D5364BD59D25D2E12D545016 at twotoe.com>
>Content-Type: text/plain;       charset="iso-8859-1"
>
>
>Just wanted to bounce some thoughts off the group:
>
>I have a Samsung GCRU and I need to permanently tap the 1PPS signal.
>
>Can the PPS output of the GPS RX be used without interfering with 
>the accuracy of the unit?
>
>Is there is another PPS output, preferably buffered and in phase 
>from the GCRU?
>
>If I am forced to use the GPS RX PPS output, at this stage I would 
>use either a RS232 line driver, or a 74HC04 to buffer the output.
>
>What sort of problems should I look out for?
>
>
>Happy holidays,
>Mark
>
>
>
>
>------------------------------
>
>Message: 3
>Date: Fri, 26 Dec 2008 23:28:51 +1300
>From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>Subject: Re: [time-nuts] Happy Holidays
>To: Discussion of precise time and frequency measurement
>         <time-nuts at febo.com>
>Message-ID: <4954B1E3.3040004 at xtra.co.nz>
>Content-Type: text/plain; charset=ISO-8859-1
>
>Bruce Griffiths wrote:
> > Richard H McCorkle wrote:
> >
> >> Ho Ho Ho
> >>
> >> Merry Christmas from the far north to all the
> >> Time-Nuts. As a gift for the holidays I have
> >> created a free version of the PICTIC for you
> >> and Didier has kindly posted the files at:
> >>
> >> http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic
> >>
> >>
> >> And to all a good night,
> >>
> >> Richard
> >>
> >>
> >>
> >>
> > Richard
> >
> > Your analog interpolator needs a little work.
> > The switching speed of the 2N3906's is so slow because the 2N3906's that
> > switch the current to ground or into the 470pF cap are saturated.
> > They will switch much faster if used as current mode switches.
> > In fact you can just replace the 2N3906 whose collector is connected to
> > the 470pF cap with a fast switching diode and the current source will be
> > switched much faster.
> > The 2N7000's have a relatively high non linear output capacitance
> > replacing them with something like 1/6X 74HC05 would be better.
> > The 470pF silver mica caps will have relatively large dielectric 
> absorption.
> > NP0/C0G caps would be a better choice, particularly if higher input
> > pulse rates were to be used.
> >
> > Have you actually measured the linearity of the interpolator?
> >
> >
> > Bruce
> >
> >
> >
>The quickest fix is to drop the differential drive to the 2N3906's and
>bias the base of the 2N3906 whose collector is connected to the 470pF
>cap at +2.5V.
>This will ensure the 2N3906's switch much faster.
>The maximum voltage on the 470pF cap should be about 1V to avoid
>saturating the transistor whose collector is connected to it.
>The opamp gain network should then be adjusted to produce the required
>output swing.
>If the maximum charging time of the capacitor is 400ns then the charging
>current should be about 4.7E-10/4E-7 or about 1.2mA.
>The 2N3906's will switch a bit faster if the current is increased to 5
>or 10mA in which case the 470pF cap should be replaced by a ~2nF cap
>(with 5mA charging current).
>Use an NP0/C0G for low dielectric absorption.
>
>Bruce
>
>
>
>------------------------------
>
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>End of time-nuts Digest, Vol 53, Issue 101
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