[time-nuts] Another use for a Trimble Thunderbolt
golgarfrincham at gmail.com
Thu Dec 25 20:11:23 EST 2014
>’d say that the plot is telling the truth. It also seems to be giving
>you information fast enough that thermal drift and barometric pressure
>is not to big an issue. If you had to wait a day or three for the same
>data, drift would be a much bigger issue. Yes, when you get to the
>“close enough” trace, drift may be an issue. (yes close enough is
>indeed close enough …).
Keep in mind that I'm talking about using a GPS signal from a Thunderbolt
to adjust a common rubidium standard that would be used in a telco or
other piece of general test equipment and thermal drift and barometric
pressure effects are never an issue for me.
>I suspect that if you try the trick with something way far off frequency
>(many 10’s of ppm), the GPS may not play nice. At any normal tune range
>on an Rb, it should be fine.
Actually it does play nice-very nice over any range I'm interested in. Keep
in mind that I wanted a simple method that would work with a 10 Mhz
standard to give me closer readings than I could get by watching the scope
the counter. I can easily use just the counter to check the frequency of a
less than stellar oscillator so what I'm describing would be used with a
fairly close 10 Mhz frequency standard and not one that isn't even close.
The Pendulum CNT-81 frequency counter I have can display a 10 Mhz error to
decimal places in 10 seconds using the math function and an external time
Anyone who has used a WWVB comparator remembers the plot zipping back to
zero position when the plotted frequency difference would exceed the
maximum deflection. The Thunderbolt's display on Lady Heather works exactly
the same way. If you look at the plots in the link that follows you will
see that the 10 Mhz appears very stable but it is actually set by a
to be 10,000,000.025000 hz in the upper trace and so to keep it in the
center position on the graph I have an oscillator offset of -2500 PPT in
Heather. In the lower trace the synthesizer frequency is set to
and the offset is -1000 PPT to keep the 10 Mhz trace centered. The
the synthesizer and the Thunderbolt is the GPS signal from the Tbolt so the
reference is used for everything.
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