[time-nuts] Another use for a Trimble Thunderbolt
warrensjmail-one at yahoo.com
Fri Dec 26 16:29:15 EST 2014
>Take a look at the plot where I adjust a rubidium standard and see what you
I think it is a great idea, and shows that LadyHeather and a modified TBolt
can make a great high end, stand alone Time-Nut tester without the need of a
reference osc or offset osc, or any other special counters.
(your plots show a great antenna and position setup, an important first step
to get the low phase noise desired)
To speed up the initial frequency tuning, what I've found helps is to set
LadyHeather's display filter to around 100 sec, then the freq offset plot
can be used to course tune the Rb's freq to under 1e-11 in just a few
After the course freq adj, if you want better than that, the phase plot can
be used to measure freq, tempco, and/or aging of any 10 MHz osc with better
than 1e-13 / day resolution or 1e-14 using a week long test run.
That should be useful for any time nut's Oscillator, even those with Cs and
Attached is a 13 day lady Heather test plot of a LPRO Rb that I did a few
years back using a Tbolt modified to use an external Osc.
The plot shows a best case undisciplined drift rate of 20 ns change over 3.5
days, 6ns /day, which equals to a 0.67e-13 freq error during days 9-11,
Then right after that at day 12, 5ns /hr for a freq error of ~1e-12.
> Date: Thu, 25 Dec 2014 20:11:23 -0500
> From: Arthur Dent
> Subject: [time-nuts] Another use for a Trimble Thunderbolt
>>’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.
> 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
> 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
> 10,000,000.010 hz
> and the offset is -1000 PPT to keep the 10 Mhz trace centered. The
> reference for
> the synthesizer and the Thunderbolt is the GPS signal from the Tbolt so
> reference is used for everything.
> On Dec 24, 2014, at 8:28 PM, Arthur Dent <golgarfrincham at gmail.com> wrote:
> Those of you who know I had hacked the RFTG-u REF 1 GPS years
> ago and had one running for 4 years before other time nuts
> discovered these units probably won't be too surprised that
> I have tried another hack that may have limited interest but
> works for me.
> Having owned a large number of Thunderbolts, I ran across a
> few that needed repairs of various sorts. One of these had
> a defective oscillator so I removed the OXCO and brought the
> EFC and 10Mhz connections out through the side of the case with
> SMA connectors so I could test various oscillators, as others
> have done before. Then I got to thinking that if I connected the
> Thunderbolt up to run and output to Lady Heather but connected
> a free running oscillator to the 10Mhz input, ignoring the EFC
> connection, it might work as a comparator to plot the drift of
> the free running oscillator. I have a few Efratom/Datum Rubidium
> standards I'm adjusting and I can watch drift on my scope at 5
> ns/cm or the 10 Mhz output to the 5th decimal place on my Pendulum
> CNT-81 counter and try to determine which way it's drifting but
> that gets old pretty fast.
> The 10 Mhz output from Lady Heather appears to be an instantaneous
> reading so that always looks very good but the PPS output appears
> to be the cumulative signed difference between the GPS and the free
> running oscillator. The link is to a plot from Lady Heather with
> just the 10 Mhz and PPS signals on the screen. The EFC is still
> trying to control the oscillator but seeing it isn't connected
> the readings could range from a meaningless 0-5 volts and I don't
> care about the temp plot either. I also know that there are other
> ways of doing this but the definition of "yankee inginuity' is
> doing things the hard way. I could also check an RFTG-u REF 1 with
> the antenna off to see how well it keeps to the correct frequency
> on holdover. I suspect that like the Z3801 it tries to predict and
> adjust the output when the GPS signal goes away. Take a look at the
> plot where I adjust a rubidium standard and see what you think.
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