This is coming, Nige; see Wayne's msg on the reflector on 15 June at
00:15:39 ....
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There appears to be more demand for this than we thought, so we're
looking into it again.
Note that our planned external reference implementation would not
require an exact 49.380000-MHz reference oscillator signal. It also
doesn't require a pin-1 control voltage input on the TCXO module itself,
as suggested earlier. It should work with any existing K3 TCXO, either
+/- 5 or +/- 1 PPM.
If you're interested, here are the details:
A new REF-lock module would be designed that plugs into the small 8- pin
connector near the top of the KREF3 PCB. The user's 10-MHz reference
signal would be routed from the rear panel to the TMP connector on the
KRE3 (this connector faces forward, into the DSP/ front panel area).
A microcontroller on the REF-lock module would be clocked by the 10- MHz
reference. If the signal were present, the microcontroller would
continuously measure (and average) the frequency of the 49.38 MHz
oscillator, obtaining a value to the nearest 1 Hz. Hysteresis would be
applied to prevent "hunting," so the actual accuracy spec would probably
be +/- 2 Hz. This translates to about +/- 1 Hz in operating frequency on
20 m.
Approximately once per second, the module would report the actual
reference frequency to the K3's main MCU via a slow digital data line
(labeled "100HZ" on the RF and KREF3 schematics). The main MCU would use
this to calibrate the REF CAL value normally entered by the user. There
would be no noticeable impact on performance.
If the 10 MHz external signal were not present, the user's normal REF
CAL value would be used.
Let me know if you have thoughts on this implementation.
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73 de David G4DMP
In a recent message, Nige <
[hidden email]> wrote ...
>
>Wow that was a close one. I was planning to buy a loaded K3 + P3 as a
>back-up radio for my Flex 5K which does have an external reference
>input. The cart was loaded to go but now I know the K3 doesn't have
>this capability this is very disappointing and I'll have to reconsider
>what to do with my money.
>
>This really is a shame.
>
>Nige.
>G7CNF
--
David G4DMP
Leeds, England, UK
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