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 retarded. 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 minute.http://tufi.alphalink.com.au/time/nsc_vng_leaflet.pdf 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 each morning. 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 tape recorders. Various schemes were tried for syncing portable recorders and remote calibration circuits. 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. Blair Lade Australia --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
