Posted by
Matt Zilmer on
Apr 05, 2011; 3:40pm
URL: http://elecraft.85.s1.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242158p6242772.html
Thanks Paul. Good summary and reference info.
The K3EXREF certainly works as advertised. I've already used two
different Rb sources, and it's solid as a rock. Using a TIA over the
weekend,, saw a 1 to 2 Hz wander at 28MHz, however the Rb clocks have
a little start-up drift and the wander might have been due to that.
And of course, the TIA is based on Rb, itself.
I bought a Rev E Thunderbolt GPS-DO from a vendor on eBay. It's still
training (< 24 hours), and there was a 1 Hz per 10 minutes upward
drift after two hours of operation, in the REF*CAL indicator. Is this
normal? Will check it again at around 24 hours into the experiement.
Even though I work in the GPS industry, I've never used a GPS-DO
before.
I've tossed my original Wellnav OCXO-based freq source. We use these
as a time base here in our GPS simulators, but they're far from phase
noise free and there is significantly more drift (might also be age).
Was seening 5 to 6 Hz of wander, and sampling it showed a textbook
[but skewed] Gaussian distribution. The wander should not generally
even be detectable with conventional ham equipment, but it was.
Cool stuff.
Just to reinforce Paul's comments, the Trimble software is quite
impressive. I work in the industry, and I've never seen even in our
own Pro products, so much monitored statistical and operations data in
a control program. It certainly was worth the price (see Trimble's
web site under Support). Free that is.
I'm running the Tbolt on a linear supply. It's a three-output Topward
lab-grade PS. Monitoring the current consumed, I see the following:
+12V: 700-750 mA for startup (warming the OCXO), 40-50 mA steady state
-12V: < 20 mA continuous
+5V: 370 mA continuous
Add all this up, and steady state power consumed comes to about 2.7W.
This is perfect for use in a solar-powered station. My K3 and general
station power comes from two 50W Siemens PV panels on the roof. These
feed a charge controller and 110AH 12V AGM battery in the shack. The
lower power consumption of the GPS-DO is compatible with this set up.
I had borrowed a Brandywine unit from a buddy that works there, and it
consumed about 35W steady state. Not good for this installation.
73,
matt W6NIA
Upland, CA.
On Tue, 05 Apr 2011 08:43:46 -0400, you wrote:
>Those of you considering a GPS-disciplined oscillator for use with the
>K3EXREF may be interested in this: I recently purchased two Trimble
>Thunderbolts on the surplus market to compare against my HP 58540A and
>Brandywine GPS4 units. After several days of testing, I'm retiring the HP
>and Brandywine units. All devices have exceptionally good stability, but
>the Trimble units consume far less power, run substantially cooler, and the
>monitoring interface provides much more status information than the prior
>units.
>
>In recent discussions with John, KE5FX, he has performed phase noise
>measurements across several GPS-DO units and even various oscillator brands
>within the Trimble Thunderbolt model.
>
>
http://www.thegleam.com/ke5fx/tbolt.htm>
>Early Thunderbolts use a Piezo Corp. OCXO and when combined with GPS
>correction, its phase noise performance is good but not exceptional. By
>contrast, the Trimble-branded OCXO offers phase noise performance several
>degrees better than most other GPS-DO units near Fc. The area between 1 Hz
>and 100 Hz is usually a good indicator of the overall phase noise
>performance. It's not easy getting good numbers that distance from Fc.
>Although the phase noise performance will not carry over to the K3, it's an
>important parameter if the GPS-DO will be used in other applications or
>other transceivers that phase lock onto the 10 MHz external reference.
>
>Some suggestions:
>
>1) Look for Thunderbolts with a year 2004 Rev. E stamp. These use the
>better quality OCXO units with the Trimble-branded label. KE5FX has sampled
>several from this batch. As noted, early units with the Piezo-branded OCXO
>are worse in terms of phase noise performance. I do not know the OCXO
>quality of recent units;
>
>2) You will see Thunderbolts in a high quality case where an internal DC-DC
>converter is used. My recommendation is to avoid being tempted by the nice
>looks and what may be perceived as a "better" unit. I can almost guarantee
>that the switch-mode converters will present noise problems with your K3
>receiver -- and seen on your panadapters. I've been down that road with
>other GPS-DO units and ultimately, I scrapped the converters and fed them
>with linear supplies. Stick to the basic ugly OEM Thunderbolt module and
>feed it from a triple-output linear supply;
>
>3) Power supplies: I like OEM/off-board supplies by PowerOne, Condor, and
>International Power. They offer excellent performance and low noise. I am
>using an International Power IHBAA-40W. Also look for HBAA-40W. The user
>must add a fuse, power cord and wiring harness. It's a little more work,
>but you get a lot of performance for the money;
>
>4) Look for sellers who will accept offers. Both my Thunderbolts were
>purchased for USD $70 ea and a small shipping change.
>
>Even if you have no plans to use K3EXREF, get one anyway as a precision
>frequency reference for your station.
>
>Paul, W9AC
>
>
>
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