[time-nuts] Seismic station timing in Australia during the late 1970's
blairl at bettanet.net.au
Wed Oct 21 04:14:53 EDT 2015
At the Seismic Station in central Australia that I ran from 1974 to 1980 we
had a free running 5MHz xtal oven in our Station clock.
The clock was powered from one of our 600AHr 24VDC battery banks (UPS) and
it was 'synced' to VNG http://www.ontheshortwaves.com/VNG.html (the Oz
equivalent to WWV) via an HF radio.
The 1pps output from the clock was used to start the time base scan on an
oscilloscope and the audio from VNG was displayed on channel 1, the clock
had an adjustable divider chain that allowed the 1pps to be advanced or
The clock would 'normally be retarded until the start of the VNG tone was
just visible on the LHS of the scope trace. The operator would check for the
right second by listening for the 'long' tone at the top of the
Time was set each morning after 00UT, 9:30 local time.
Accuracy, anyone's guess but the offset was fairly constant day to day.
The operator would record the drift that was corrected in the station's log
An estimation of the propagation delay from the transmitter to our site was
taken into account when analysing the records.
The xtal oven was adjusted for a drift (fast) of a few mS for the day, this
ensured that the scope was triggered before the time signal was received ,
making it easier for the operator to check and measure the daily drift.
IRIG H (slow code) time code was generated by the clock and sent to
helicorders (waxed paper chart recorders) and low speed 0.3ips 24 channel FM
Various schemes were tried for syncing portable recorders and remote
Omega was one and the sun shining through a lens and a thin slit made from 2
razor blades onto a photocell was another.
The best however was a cheap AM receiver tuned to the local National Radio
station (ABC) who would (remotely) turn on their transmitters across outback
Australia at the same time (6am) every morning.
The carrier was detected and the portable recorders clocks 'synced'.
This worked very well when we got ours for about 2 weeks until the national
radio station went 24hrs!
No one had bothered to talk to them.
Ah, the days before GPS were so much simpler.
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