Hi
The rubidium *should* be good at the 1x10^-11 level. The GPSDO can be better
than that. The issue is that neither one is very good in the short term.
Measurement periods of hours are not unusual to get things right. If GPS
with your antenna location is good at the 10 ns level, that's 1x10^-8 per
second. 10,000 seconds will get you to 1x10^-12. That's good enough to
calibrate the rubidium. The calibration standard should always be much
better than the thing you are calibrating.
No matter what you do, it's a "watching grass grow" sort of thing. Some sort
of automation is a good idea.
One approach (of *many*):
Your GPSDO probably has a 1 pps coming out of it.
Your Racal can measure time between two 1 pps pulses (if I remember that
model correctly)
Divide the rubidium down to 1 pps and look at it relative to the Racal.
Log data out of the Racal so you can go back and see what's happened.
That's not going to work very well if the Racal does not have some kind of
serial or GPIB output.
There are a lot of other approaches. Cost can become a factor. For some
the budget for this sort of thing is quite large. For others low cost /
build it yourself is what makes sense. Are you looking at setting up a lab,
or just want to get the Rubidium on frequency?
Bob
--------------------------------------------------
From: "Raj" <[email protected]>
Sent: Sunday, February 07, 2010 10:25 AM
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Subject: Re: [time-nuts] Frequency comparison
Hi Bob,
I have a HP5350B with the oven (probably standard) continuously
powered. The Racall-Dana is with a OCXO that I have added. The Racall has
a phase comparison between A-B inputs.
I am just comparing 10 MHz frequencies. I see one cycle drift in
greater than 100 seconds to 10 minutes, painful to watch and adjust!
Raj
At 07-02-10, you wrote:
Hi
Which HP counter(s) do you have?
The method you are using now with a scope can give you good accuracy if
your clocks are close to each other and you watch things for a long enough
time.
Bob
On Feb 7, 2010, at 10:04 AM, Raj wrote:
Hi! all Time-Nuts,
For a newbie like myself at GPSDO & Rb oscillators etc. what
method of frequency comparison would you gurus recommend ? Any articles
on this subject ?
Available test instruments are: Scopes digital & Analog, counters
with 0.01 Hz display at 10 Mhz (HP & Racall-Dana).
Currently I am comparing the phase between two 10 Mhz and
adjusting for the lowest drift visually on the scope and phase drift on
the Racall-Dana 1992.
Your suggestions I would like to use for calibrating the Rb
oscillator with a GPSDO.
Regards
--
Raj, VU2ZAP
Bangalore, India.
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--
Raj, VU2ZAP
Bangalore, India.
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