The few experiments I've done indicate that there isn't that much
sample-to-sample jitter in a divider built up out of a reasonable-length
string of 74HC390 dividers, but the temperature stability is horrible.

John

I need to find the best way to go from the 10 MHz sinewave to the
divider, probably through an LM119 comparator with modest
hysteresis.

Didier,

I've been out of town and I see a flurry of postings to
your original query about Allan deviation. It sounds
like your goal is to measure the stability of various
oscillators that you have lying around?

First, your 5370 or any other TIC (Time Interval Counter)
will be adequate for this. I'd suggest using a 'scope on
the input channel(s) to make sure your signal and trigger
levels are what you think they are. Outliers or high 5370
STDEV is a hint of poor triggering.

It sounds like you have the computer data logging part
solved. Most ADEV tools take accumulated phase
difference data; just the data that a 5370 in TI mode
will generate.

Second, your Jupiter GPS board, or any other sub-100 ns
GPS timing board, will work fine. Use the 1PPS output.

You don't have to build a GPSDO in order to make the
measurements that you want! In fact, it may only get
in the way. Instead, consider these two points.

1. For short-term stability tests, just make a set of
   quick pair-wise measurements between stand-alone
   oscillators at short gate-times. If they are close in
   frequency, or can be made close in frequency, then
   the 5370 built-in STDEV statistic is useful in real-time
   (use an N or 10 or 100). If not, collect raw phase data
   and run it through your favorite ADEV tool.

This method should work fine for fractions of a second
to 10s or 100s of seconds.

The good and bad pairs will be obvious; in a matter of
minutes you can tell which one or two oscillators are
the best, short-term.

Remember that your measurements are the RMS sum
of both oscillators and the counter itself so there will be
limits to the resolution, especially visible at short times.

2. For long-term stability measurements, one at a time,
   compare your oscillators against the raw GPS 1PPS,
   collect phase data, and run it through your ADEV tool.

To avoid phase wrap-around, depending on the frequency
offsets, you may need to divide the 5/10 MHz oscillator
down to at least the kHz range, or the obvious 1PPS, to
get clean phase measurements.

Let the GPS 1PPS be the start channel. For this sort
of long-term measurement any TTL/CMOS homebrew
divider will work (the jitter and tempco are in the noise).

It's OK to average the samples down by 100 to 1000
to reduce the volume of data you collect or process.
I often use something around 300 (5 minutes).

This will give you frequency offset, mid- to long-term
stability, and frequency drift information. A couple of
hours or days of data per oscillator should be sufficient.

Again, you don't need to build a GPSDO for any of this.

/tvb

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Tom

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?

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?

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.

the Datum LPRO User's Guide / Installation Guide discusses some methods
of sine to square wave conversion in terms of lowest phase noise.

Since you were originally asking for Allan Deviation i would like to
advertise again my free PLOTTER software which does what ALAVAR does but
more nicely + many things more. Since it does not simply open the input
file but first makes a copy to a "working file" you may even work with
it on files in that a different program is currently sampling data, so
you don't have to wait to the end of data acquistion but may get
intermediate results at any time.

When you put forward your questions about measuring Allan deviation i
saw that it were all the right & intelligent questions and perhaps this
is the reason why so many people are willing to enlighten you. I wish I
had known time nuts when i was in the same state of mind as you. Would
have saved me years of learning it the hard way!

73 de Ulrich, DF6JB

Didier,

I've been out of town and I see a flurry of postings to
your original query about Allan deviation. It sounds
like your goal is to measure the stability of various
oscillators that you have lying around?

First, your 5370 or any other TIC (Time Interval Counter)
will be adequate for this. I'd suggest using a 'scope on
the input channel(s) to make sure your signal and trigger
levels are what you think they are. Outliers or high 5370
STDEV is a hint of poor triggering.

It sounds like you have the computer data logging part
solved. Most ADEV tools take accumulated phase
difference data; just the data that a 5370 in TI mode
will generate.

Second, your Jupiter GPS board, or any other sub-100 ns
GPS timing board, will work fine. Use the 1PPS output.

You don't have to build a GPSDO in order to make the
measurements that you want! In fact, it may only get
in the way. Instead, consider these two points.

1. For short-term stability tests, just make a set of
   quick pair-wise measurements between stand-alone
   oscillators at short gate-times. If they are close in
   frequency, or can be made close in frequency, then
   the 5370 built-in STDEV statistic is useful in real-time
   (use an N or 10 or 100). If not, collect raw phase data
   and run it through your favorite ADEV tool.

This method should work fine for fractions of a second
to 10s or 100s of seconds.

The good and bad pairs will be obvious; in a matter of
minutes you can tell which one or two oscillators are
the best, short-term.

Remember that your measurements are the RMS sum
of both oscillators and the counter itself so there will be
limits to the resolution, especially visible at short times.

2. For long-term stability measurements, one at a time,
   compare your oscillators against the raw GPS 1PPS,
   collect phase data, and run it through your ADEV tool.

To avoid phase wrap-around, depending on the frequency
offsets, you may need to divide the 5/10 MHz oscillator
down to at least the kHz range, or the obvious 1PPS, to
get clean phase measurements.

Let the GPS 1PPS be the start channel. For this sort
of long-term measurement any TTL/CMOS homebrew
divider will work (the jitter and tempco are in the noise).

It's OK to average the samples down by 100 to 1000
to reduce the volume of data you collect or process.
I often use something around 300 (5 minutes).

This will give you frequency offset, mid- to long-term
stability, and frequency drift information. A couple of
hours or days of data per oscillator should be sufficient.

Again, you don't need to build a GPSDO for any of this.

/tvb