[time-nuts] Time Nuts at PTTI this past week

Tom Clark, K3IO K3IO at verizon.net
Sat Dec 9 01:27:47 EST 2006


This past week, a number of use gathered in Reston, VA for the 38th
annual PTTI (Precision Time & Time Interval) meeting (see
http://tycho.usno.navy.mil/ptti/ptti2006/ptti2006.html). The attendance
list included

Tom van Baak (no call, but known to the world as TvB, Seattle)
Jim Jaeger(K8RQ, Cincinnati)
Peter Lothberg(SM4KEL/W4KEL, Stockholm)
Bob McGwier (N4HY, Princeton)
Doug Hogarth (K4UTC, Seattle)
Rick Hambly (W2GPS, Balto/Wash)
Tom Clark (K3IO, Balto/Wash)
Jim DeYoung(KG4QWC, Alexandria)
Clive Green(G3???, UK)

In the list above are counted 8 privately owned H-Masers, nearly 20
Cesium clocks and countless Rubes and precision quartz units. Jaeger's
wife always encourages him to go to the annual PTTI "Time Camp" so that
she can have a week of quiet time.



On the program, TvB made the biggest hit. On Wednesday nite, he gave a
stunning presentation on his GRE²AT experiment. GRE²AT stands for the
General Relativity Einstein/Essen Anniversary Experiment in 2005 -- a
celebration of the 100th anniversary of Einstein's Theory of General
Relativity (http://www.pbs.org/wgbh/nova/einstein/genius/), and the 50th
anniversary of Essen's first Cesium Beam clock and the determination of
9,192,631,770Hz as the resonant frequency of Cs
(http://tycho.usno.navy.mil/cesium.html).

Tom told about his personal clock collection, his lifetime fascination
with the topic. He finally got to GRE²AT. His wife told him to get their
3 kids out of the house for a few days, so he loaded up his minivan with
3 of his 5071 Cs standards and took off for Mt. Lassen. The change in
altitude caused a frequency shift that, when totaled for 3 days,
amounted to a clock offset of ~22 nsec with respect to his "at home"
clock bank. The problems of keeping the 3 clocks running, as well as
keeping the minivan running (to provide air conditioning) despite
campers being curious about the effects of bing so close "Atomic Clocks"
with blinking lights gave everyone a good laugh. The entire audience
cited the paper as the highlight of the conference. I hope this note
will cause Tom to post his PowerPoint presentation for all to see.



I presented a paper by Rick and me entitled "Improving the Performance
of Low Cost GPS Timing Receivers". This described our continuing saga in
providing GPS timing clocks for the world (and especially my VLBI
colleagues) starting with my TACs and evolving into Rick's commercial
CNS-I and CNS-II Clocks. We described the circuit we use to remove the
sawtooth dither to the ~1 nsec level. Rick incorporates the sawtooth
remover in his CNS-II (see http://www.cnssys.com)

We then reported on our evaluation of four versions of Motorola's M12
timing receivers [two software releases of the M12+, an in-house
prototype of the new M12M and an early prototype of the iLotus M12M --
the first three have "DC" timing offsets of < 10 nsec to our "Gold"
receiver that was calibrated at USNO 4 years ago while the iLotus
prototype shows ~30 nsec of DC bias].

I'm certain that Rick & I will have the PowerPoint slides from our paper
available for all this week at http://gpstime.com. I'll let you know
when it has been posted.

73, Tom







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