[Elecraft] K3EXREF and Trimble Thunderbolts

Tue Apr 5 10:17:55 EDT 2011

Joe,

Sure.  One could build a clean supply using 1A regulators from a 
well-filtered supply.  The requirement is +12, -12, and +5.  So, one could 
use 7812, 7912, and 7805 regulators -- or their low drop-out LM2940 
equivalents.  I believe the max current needed during oven warm-up is about 
0.75 amp from the +12V supply and that tapers off to quite a bit less 
afterwards.

The trouble with many homebrew power supplies is lack of attention paid to 
filtering before and after the regulators -- and sizing the voltage drop 
across the regulator to account for brown-out conditions but no more. 
Probably the majority of builders neglect the inclusion of film caps and 
discharge diodes around the regulators.

I believe the latest ARRL handbook includes good information about power 
supply construction and how to go about matching up the transformer to 
adequately hit the regulator input target voltages based on rectifier type.

OTOH, new-old-stock supplies (e.g., PowerOne, Condor, International Power) 
can be found on-line at a cost comparable to what one would pay to build a 
supply using new components.  I paid about $35 for a NOS triple-output 
supply made by International Power.

Paul, W9AC

----- Original Message ----- 
From: "Joe Subich, W4TV" <lists at subich.com>
To: "Paul Christensen" <w9ac at arrl.net>
Cc: <elecraft at mailman.qth.net>
Sent: Tuesday, April 05, 2011 10:05 AM
Subject: Re: [Elecraft] K3EXREF and Trimble Thunderbolts

>
> Paul,
>
>> 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.
>
> What are the power requirements?  Would it not be possible to build
> a basic linear supply relatively inexpensively and avoid all of the
> switcher issues?
>
> 73,
>
>    ... Joe, W4TV
>
>
> On 4/5/2011 8:43 AM, Paul Christensen 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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