Re: K3EXREF and Trimble Thunderbolts

Posted by Rich Heineck on Apr 05, 2011; 6:32pm
URL: http://elecraft.85.s1.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242158p6243359.html

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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