[time-nuts] Measuring frequency rather than tuning crystal

[jpbridge at aol.com]

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.alfille at gmail.com>
To: jpbridge <jpbridge at aol.com>; Discussion of precise time and frequency measurement <time-nuts at 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 at 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.alfille at gmail.com>      
 To: Discussion of precise time and frequency measurement <      time-nuts at 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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