All I was saying was most modern frequency counters, including my relatively
cheap TTi TF930 have closed box calibration - you apply 10MHz as part of the
calibration procedure and then it presumably stores constants internally. There
is no tuning of the crystal. I think that much higher end counters such as the
newer Keysight and Tektronix (rebadged Pendulum) do the same.
It probably doesn't do any thermal calibration, purely frequency scaling at
room temperature.
So your proposal for your own set up should work fine.
I wasn't suggesting that it calibrates itself from GPS - but in theory you
probably could automate the process but if you had a GPSDO available all the
time you might as well just use it as the reference input.
James
-----Original Message-----
From: Paul Alfille <paul.alfi...@gmail.com>
To: jpbridge <jpbri...@aol.com>; Discussion of precise time and frequency
measurement <time-nuts@febo.com>
Sent: Fri, 27 Feb 2015 20:09
Subject: Re: [time-nuts] Measuring frequency rather than tuning crystal
I don't think your TTi TF930 has a GPS input to calibrate against, based on a
quick perusal of the data sheet. I would guess that the calibration constants
are thus fixed from the factory (including temperature coefficients).
On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts <time-nuts@febo.com>
wrote:
I presume that this is what my TTi TF930 does. Calibration is closed box so I
guess the TCXO is free running and the micro inside just uses calibration
constants.
James
-----Original Message-----
From: Paul Alfille < paul.alfi...@gmail.com>
To: Discussion of precise time and frequency measurement <
time-nuts@febo.com>
Sent: Thu, 26 Feb 2015 19:02
Subject: [time-nuts] Measuring frequency rather than tuning crystal
I have a couple of HP 5370s with the beaglebone brain transplant. They
come
with a nice 10811 that has a little adjustment screw.
Testing against a
Thunderbolt or KS-24361 the 5370 is off by less than 1Hz.
I know the
traditional method would be to adjust the crystal slowly and
make careful
measurements, but since I have a fancy computer in there, I
wonder if I could
just adjust the frequency in software. 64-bit floating
point numbers should
have sufficient accuracy. All reported measurments
would be corrected for the
actual reference frequency.
Basically, I'd have a 10000000.226 Hz internal
reference.
In fact, could I connect the beaglebone to a a GPS 1 pps source
and make
this a GPS-disciplined-software-corrected oscillator.
So my
question is is this a known technique? The discipline feedback
circuit seems a
little different, I'd adjusting for drift and offset, but
not the gain of
control-oscillator
linkage.
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