[time-nuts] HP 5372A vs. 5370A

[SAIDJACK at aol.com]

Hi Ed,
 
excellent email. You raise the SNR of this forum!
 
I have tried to measure the CW-12 output myself with phase noise and Allan  
Deviation equipment, and the constant cycle jumps prevent these from giving 
 sensible results. Both PN and ADEV plots look awful, many orders of 
magnitude  noisier than even an average oscillator. Glad to know that  your 5372A 
could get the job done.
 
btw: jumping cycles 200 times a second is not disciplining an oscillator,  
it's numerically controlling a frequency. Thus the CW-12 cannot  be 
considered a GPSDO due to the massive 8ns phase jumps. But for many  apps such as 
driving a microprocessor clocks this may be good enough, even  though one has 
to be careful that their internal PLL's can lock to such a noisy  (jumpy) 
source. Of course the number of corrections per second should have  a very 
strong correlation to temperature as the TCXO used on the CW-12 drifts  over 
temperature.
 
bye,
Said
 
 
In a message dated 2/9/2011 13:14:16 Pacific Standard Time,  
ed_palmer at sasktel.net writes:

The  CW-12 also has a 10 MHz output.  I used the Histogram Time Interval  
function to measure the periods of 100 Million cycles with a resolution  
of 200ps.  It took less than 30 seconds to measure, process, and  display 
the results.  The results showed that there was a normal  distribution 
around 100 ns and a second normal distribution around 92  ns.  The 
difference is approximately the period of the internal clock  (120 MHz).  
This told me that the 10 MHz is kept on frequency by  occasionally 
shortening the period by one cycle of the internal  clock.  For my unit, 
this happens about 200 times a second.  I  know this by the ratio of the 
number of long periods to short  periods.  This behaviour explains why 
Navsync warns that this output  needs to be cleaned up before using it as 
a frequency  reference.