2008/10/12 Bruce Griffiths <[EMAIL PROTECTED]>: > Steve Rooke wrote: >> 2008/10/12 Myers, Charlie <[EMAIL PROTECTED]>: >> >>> Hello to the Time Nuts, >>> >>> I have been reading the mail on this topic for the last week or so with >>> great interest. Lots of interesting ideas have been put forth for >>> measuring frequency to a high degree of precision and for comparing a 10 >>> MHz clock's frequency to a highly accurate 10Mhz frequency "standard". >>> >>> The way I measure the frequency of a 10 MHz clock is to compare it to a >>> second 10MHz clock of known accuracy and stability, not only with a >>> frequency counter but also with a phase meter. >>> >>> I have several GPS disciplined OCXO's, one GPS disciplined Rubidium >>> oscillator, and several free running rubidium oscillators. I measure >>> the frequency of an unknown 10 MHz clock using a 2 step process. First >>> I measure the unknown 10 MHz clock using an HP 5384A reciprocal counter >>> that employs my known 10 MHz clock as its external timebase. I set the >>> gate time to 10 seconds and the counter delivers a frequency measurement >>> with a resolution of less than 3 mhz (3 millihertz). So, assuming my >>> known timebase is "bang on", I know the frequency of the unknown 10 MHz >>> source to an accuracy of roughly 3e-10 or 3 parts in 10 billion. >>> >>> To get a more precise measurement of the frequency difference between >>> the two 10 MHz clocks, I supply the known 10 MHz clock to the Channel A >>> input of an HP 3575A Gain-Phase meter and the unknown 10 MHz clock to >>> the channel B input of the Gain-Phase meter. I measure the change in >>> the phase angle between the 2 input clocks over some convenient time >>> interval (e.g., 10, 100, or 1,000 seconds) and compute the frequency >>> difference using the formula: >>> >>> >>> Frequency Difference = [Change in Phase Angle (in degrees) / Measurement >>> Duration (in seconds)] X [1 / 360] >>> >>> The frequency difference can then be converted to frequency accuracy >>> using the formula: >>> >>> Accuracy = Frequency Difference / 1e7 >>> >>> >>> This seems like a pretty straight forward technique. Am I missing >>> something? >>> >> >> So what's time nutty about this method... >> >> :) >> > Using ~40 year old boat anchor rackmount equipment to measure something > that can be done more accurately with a handful Of ICs.
That would surely just make it nutty then... -- Steve Rooke - ZL3TUV & G8KVD Omnium finis imminet _______________________________________________ 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.
