[time-nuts] Trimble NTGS50AA DAC Voltage

GandalfG8 at aol.com GandalfG8 at aol.com
Wed Jun 11 20:24:50 UTC 2014


I don't recall seeing this mentioned here before but if it has been, or if  
it's just something everyone else has always taken for granted, then  
apologies in advance from a comatose brain cell for the wasted  bandwidth.
 
Until today I'd not previously seen either an NTGS50AA or an NTBW50AA where 
 the unconditioned oscillator frequency was above 10MHz, this from  a vast 
sampling of three of one and two of the other, so perhaps not  quite the 
stuff of certainty:-), and because I'd only ever seen the EFC  voltage ramping 
upwards from it's starting point of 3 Volts had just  assumed that the 
fitted oscillators had been specified or selected such  that a 10MHz output was 
always achieved with an EFC voltage somewhere  between 3 and 6 Volts.
 
I have wondered at times why just this limited range was used but  hadn't 
actually paused to consider whether or not I might be seeing  less than the 
full picture.
 
Testing an NTGS50AA today with an oscillator that started, after  initial 
warm up, at a frequency of 10.000 000 4xx MHz, I was thus fully  expecting 
the EFC voltage to ramp upwards as "usual", and  that the unit would 
eventually report a bad oscillator after  the EFC had reached 6 Volts without the 
oscillator frequency crossing 10 MHz, so  was quite intrigued when the EFC took 
the more logical step of ramping  downwards instead.
So much for jumping to conclusions:-)
 
At this stage I still wasn't sure whether or not this was a  fully 
automated process or the result of some form of "select on test"  procedure, but 
subsequent tests feeding a variable 10MHz signal from an HP3336  generator into 
another NTGS50AA modified to use off board oscillators have shown  that the 
NTGS50AA, so presumably also the NTBW50AA, will adapt on the fly  to 
accomodate an EFC range of 0 to 6 Volts from the "rest" position of a nominal  3 
Volts.
 
It is a bit sad watching the poor thing chasing its tail when the  
frequency it's seeing isn't actually under its control after all, but  overall a 
much more satisfactory outcome than my original misguided  assumptions:-)
 
Regards
 
Nigel
GM8PZR
 
 
 


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