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 > > > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:Elecraft@mailman.qth.net > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
