> a related very interesting experiment is to take the Horizontal Sync signal > from an old Tube-type TV, and feed it to a frequency counter with GPSDO time > base (preferrably). > > Got to be careful about the high voltages inside the TV though!
If you use proximity EM field pickup you don't even have to be careful. That's how some of the amateur TV frequency standard projects worked. > BTW: it's not 15374KHz, there are some significant decimal digits (I don't > recall the formula to calculate the frequency exactly, but it was the total > number of frame lines multiplied by 59.94Hz or so). You can see why, in the pre-GPS 1970's, color television carriers were useful as lab frequency standards. Sample NIST papers: Precision and Accuracy of Remote Synchronization Via Portable Clocks, Loran-C, and Network Television Broadcasts http://tf.nist.gov/timefreq/general/pdf/760.pdf Nationwide Precise Time and Frequency Distribution Utilizing an Active Code Within Network Television Broadcasts http://tf.nist.gov/timefreq/general/pdf/1601.pdf Long-Term Continental U.S. Timing System Via Television Networks http://tf.nist.gov/timefreq/general/pdf/237.pdf Exact numbers for NTSC color television are: subcarrier, Fsc = 5 MHz x 63 / 88 = 3 579 545.454 Hz (~3.58 MHz) line rate, Fh = Fsc / 455 = 15734.265 Hz note 455 = 5 x 7 x 13 field rate, Fv = Fh / 525 / 2 = 59.940 059 Hz note 525 = 3 x 5 x 5 x 7 Equivalently: Fv = 60 Hz x 1000 / 1001 = 59.940 059 Hz note 1001 = 7 x 11 x 13 Fh = 4.5 MHz / 286 = 15734.265 Hz note 286 = 2 x 11 x 13 Fsc = Fh x 455 / 2 = 3 579 545.454 Hz note 455 = 5 x 7 x 13 For those of you who like prime numbers, number theory, tube multivibrators, in addition to being a time nut (or does that narrow it down to just me?), my favorite TV time/frequency article is: A Tutorial on Magic Numbers for High Definition Electronic Production http://www.poynton.com/PDFs/Magic_Numbers.pdf For a less mathematical treatment see: http://en.wikipedia.org/wiki/NTSC http://www.edlmax.com/AudioNTSC.htm http://stjarnhimlen.se/tv/tv.html#FRAMERATE http://www.theiabm.net/Technology.aspx?i=10 http://www.goupi.org/analogtv.html http://www.quantel.com/site/en.nsf/html/library_dfb to download the Quantel Digital Factbook in PDF format /tvb http://www.LeapSecond.com _______________________________________________ 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.
