http://elecraft.85.s1.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242158p6243555.html
You are correct on #1 and #2, as long as the signal amplitude feeding the K3EXREF is in
the range of +4 dBm to +16 dBm. The Thunderbolt 10 MHz output is typically +12dBm (about
> 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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