[time-nuts] FMT on October 13
didier at cox.net
Mon Sep 24 21:40:01 EDT 2007
I guess it depends on signal to noise ratio. With reciprocal counters, you
only need one period to measure as acurately as you need, but to have good
acuracy, you need very good S/N, as there is no filtering possible.
For example, the HP 5370 can measure a single period of a signal with a
resolution of 20pS (excluding noise and trigger imperfections), so excluding
these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal
with 7 x10-5 precision (if I have not goofed the calculations....) More
periods improve the resolution proportionately to the quare root. Accuracy
is another matter.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Hal Murray
> Sent: Monday, September 24, 2007 5:26 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] FMT on October 13
> > Plans are to transmit two 10 minute test periods, and a
> third if the
> > transmitters aren't melting by that point.
> > Our goal is to transmit a signal known in frequency to
> parts in 10e-12
> > (i.e., less than 0.0001 Hz error at 10 MHz) and stable to a similar
> > level during the course of the transmission. Frequencies will be
> > measured at the transmitter site with a system capable of
> > resolution referenced to a GPS disciplined oscillator, and
> will also
> > be monitored by another station in groundwave range that
> can measure
> > the frequencies with similar accuracy.
> Suppose I have a pile of good lab gear, and it gets N seconds
> of signal.
> How accurately can it measure the frequency?
> These are my opinions, not necessarily my employer's. I hate spam.
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