[time-nuts] Frequency Stability of Trimble Mini-T

SAIDJACK at aol.com SAIDJACK at aol.com
Thu Oct 16 20:23:31 UTC 2008


Hello Mike,
 
let me take the commercial discussion offline with you, and let me try to  
answer the time-nuts questions for you:
 
>  When you say the EFC voltage changes by several millivolts,  how much
>  does that change the crystal frequency?


Actually, the average frequency doesn't change at all, it is being  held at 
10.0MHz by the GPS reference. What does change is the control voltage  that the 
crystal wants to see to generate exactly 10.0MHz.
 
But let's say you kept the EFC voltage constant, say by disconnecting  the 
GPS antenna, then it is simple to calculate the frequency change the OCXO  
experienced due to the jump:
 
   Say there was a 500 Microvolts jump. A typical OCXO has  +/-20Hz control 
range 0V to 5V. So it's sensitivity is 8Hz/V. Now simply  multiply this by 
0.5mV:
 
   8Hz/V * 0.5mV = 0.004Hz change of frequency
 
Or in other words, 0.004Hz/10MHz = 4E-010 change in frequency.
 
That doesn't sound significant, but would show up as a significant jump  on 
GPSCon for example.

>  if it is not confidential, can you say what kind of   phase detection
>  you use in your GPSDO?


That's a little bit confidential unfortunately :) 

>  On your page at  http://www.jackson-labs.com/products_fury.html
>  it  states:
>  "Allan Deviations  of less than 1E-011 are  possible  for measurement
>  intervalls greater than 0.1  seconds."
>  What kind of counter do you use to measure that data  point?


You can find several review papers of Jackson Labs' products written by Tom  
Van Baak on his website. He was kind enough to supply ADEV plots for our  Fury 
units, and our double oven units achieve this level of performance. I  think 
he used 53132A's for some of these plots, and TSC5120A units for the ADEV  
plots.
 
See for example his review of an early version of the Fury:
 
   _http://www.leapsecond.com/pages/fury/_ 
(http://www.leapsecond.com/pages/fury/) 
 
Please note that Tom tested an early version of the Fury firmware, and we  
have since very significantly improved the performance of the unit.

>  Further down on the same page, it states:
>  "A  high-end Motorola GPS receiver"
>  Can you tell what kind of Motorola  GPS you use?


Fury uses the M12+ and/or M12M GPS. They are now made by iLotus since  
Motorola sold their GPS operations. We also use modern 3D-capable 50-channel  GPS's 
on our newer products such as the FireFly series GPSDO.

>Finally, do  you  have  a  price list   for  the  OEM  and commercial 
products?


I will have our VP of sales discuss this with you, and send you a price  list 
offline.
 
Thanks,
Said




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