Hello fellow Time nuts, I am a newbie here, just joined, first post. But back in college dabbled in "precise time" recording in the field, for Geodetic Surveying field measurements, Star Shots. transiting the meridian. Very crude by today standards, but effective for field measurements that had to be time stamped to sub second accuracy, I got to about 3-4ms UTC absolute, and prior to my senior project most geodetic surveyors used a Wooden boxed, marine chronometer, to get sub second UT1 time, or back then, GMT. I have a project involving use of a Hydrogen Maser as a frequency reference, a STEM activity coming up next year that may be of interest, and for which I need some technical assistance. Involves precisely measuring received frequency of a lunar orbiting satellite, in the 70 cm band. over a period of an hour or so, and from widespread locations (multiple MASERS) around the Earth.
But that project will be revealed in my next post. Mean time, for your enjoyment, I copy here a summary of what/how the Arecibo Radio Telescope capabilities were, when I visited there for a moonbounce activity I set up, called "Echoes of Apollo", in 2012. Google and search Youtube videos, KP4AO for commentary. I was interested after returning home from Echoes Of Apollo, to learn more about frequency standards they had and used at the Arecibo Observatory. So I wrote and got an interesting reply from one of their awesomely knowledgeable staff. Here is his reply on Arecibo Time: "Any radio observatory worth its salt has time information at hand to the sub-microsecond level of accuracy. Having experienced only the AO, I can speak of how we do it, but can't speak for other observatories. Basically we start with a highly stable reference oscillator, an active hydrogen maser whose frequency we generally maintain within about 1 part in 10^14. It has an internal synthesizer which provides a 10-MHz output. Note that this level of frequency accuracy is needed primarily for our planetary radar and pulsar timing work, so not all observatories would be as well equipped. The 10-MHz signal is distributed about the place for locking LOs and other synthesizers, but it also "regulates" our master station clock. This clock produces time-of-day (distributed in one of the IRIG formats) and a 1 pulse per second digital output (1PPS). These are also distributed about the observatory. We compare our station clock against UTC via a "common view GPS" measurement scheme, in which we locally record time differences between our master clock and GPS signals received by a special receiver. This receiver, among other things, pays attention solely to GPS signals which come from satellites known to be simultaneously receivable both here and at NIST in Boulder at the time of each comparison measurement. Then we send our locally-recorded difference data to NIST via internet, and they apply relevant corrections and can tell us our time error with respect to UTC. We receive this information as a monthly report, whose major component is a graph of our daily average difference from UTC. We try to keep this difference within ~200 ns. It does drift around, however, because the maser itself does drift around a wee bit and even very tiny frequency errors integrate up to substantial time errors if left alone. >From time to time we make small (a few parts in 10^14) adjustments to our maser's frequency if the time error is getting too large, in order to start our clock drifting back towards correct alignment with UTC. The end result is that an observer has immediate real time access to time within a few hundred ns of correct. Further, he can do much better if he is willing to wait for the monthly report and apply the corrections- then he can get down to ~10 ns error." More, re MASER questions, later... Best, 73, Pat Barthelow AA6EG apol <[email protected]>[email protected] *"The most exciting phrase to hear in Science, the one that heraldsnew discoveries, is not "Eureka, I have found it!" but:* "That's funny..." ----Isaac Asimov _______________________________________________ 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.
