From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] How to measure Allan Deviation? Date: Tue, 24 Oct 2006 10:52:21 +1300 Message-ID: <[EMAIL PROTECTED]>
> Tom Hi Bruce, > In comparing 2 oscillators do you mean > > 1) Connecting one oscillator to the FREQ STD input at the rear of the > 5370A, selecting the external timebase and connecting the other > oscillator to the Front panel FREQ/PERIOD input and then selecting > frequency measurement which in effect gives the frequency ratio of the 2 > oscillators? I have advocated this approach, but nobody seemed to care. > OR > > 2) Connecting the 2 oscillators to the LO and RF ports of a mixer, > lowpass filtering the mixer output and measuring the beat frequency? Could potentially cause very long cycles which could mean unknown amounts of wrap in the counters time-counter. Unless you ensure them to be sufficiently offtuned so it is a very small risk. Actually, I think he meant: 0) Connect the two oscillators to start and stop channels and measure the TI results. > If the temperature varies over a large range whilst collecting PPS > timing data, any old divider will not suffice as particularly with a > CMOS ripple counter (eg cascaded 74HC390's) the propagation delay > (tempco ~ 0.4%/K) will vary significantly as will the receiver delay. You will handle that to a high degree by a synchronising D-flip-flop clocked with the input clock and taking the divided PPS for input. Then most effort is on that one alone. Cheers, Magnus _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
