[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
More information about the Time-nuts_lists.febo.com
mailing list