Re: K3EXREF and Trimble Thunderbolts

Posted by K2QI on Apr 05, 2011; 7:11pm
URL: http://elecraft.85.s1.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242158p6243491.html

Hello group,

It's been many months since I've posted here, much less actually done
something new with my K3.  This topic has however piqued my interest.
Just so I understand fully, am I right in assuming then that the
following is correct:

1.  Any reference oscillator operating at 10 MHz would work with the K3XREF?
2.  All that's needed for this to work is the K3XREF, updated
firmware, an accurate 10 MHz clock/oscillator, and a BNC cable?
3.  Trimble Thunderbolt seems to be a good, cheap product to try.  Any
others that are > $100?

What are the additional advantages of doing this other than knowing
you've pretty much eliminated any frequency drift?

73 de James K2QI
President UNARC/4U1UN

On Tue, Apr 5, 2011 at 2:32 PM, Rich Heineck <[hidden email]> wrote:

> The K3EXREF uses the 10 MHz standard as it's time base to measure the K3's TCXO and passes
> an error value to the K3's MCU every few seconds.  No TCXO frequency control takes place,
> thus no increase in phase noise.  Frequency compensation is done in software by
> automatically updating the REF CAL function.  A relatively simple mechanism but effective :)
>
> For my installation, I'm using a Thunderbolt, an $11 active antenna from Digi-Key, and a
> 30' run of RG-6, which works nicely with the F connector on the Tbolt.
>
> 73,
> Rich  AC7MA
>
> On 4/5/2011 10:35 AM, Leigh L. Klotz Jr WA5ZNU wrote:
>> ...
>> The K3XREF product that Elecraft is developing is, to my understanding, an
>> external disciplining interface for the TCXO in the K3. It's probably a
>> frequency counter / microprocessor which reads the internal oscillator and
>> the external 10 MHz reference, and when the internal oscillator doesn't
>> produce the right number of cycles in 10 million of the external
>> oscillator's cycles, it adjusts the voltage on the TCXO to bring it back
>> into spec.  But if you do this too often, you'll introduce phase noise into
>> the K3 (think of it as FM-ing).  Wayne N6KR has said it does this a few
>> times a second an has achieved a trade off between accuracy and phase noise.
>> (I presume he doesn't adjust during TX, for example.)
>>
>> I leave my K3 on most of the time, and I've found that it is seldom off more
>> than +/- 3 Hz.  But the K3XREF would let it off +/- 1Hz as soon as you turn
>> it on, provided it's hooked up to your external reference.  The actual
>> received frequency is only valid for one mode and one filter, once you
>> calibrate it, since when you shift modes or filters the offets of the
>> various internal IF stages varies.  (Keep that in mind if you use the K3 for
>> the ARRL FMT.)
>>
>> Leigh/WA5ZNU

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