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? Charlie Myers WA3RAD _______________________________________________ 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.
