[Elecraft] KREF3 External Reference Option: Detailed proposal

[Eugene Balinski]

I should not type when tired.  That should have read "this
is good", not goof....   sorry about that..

73
K1NR

On Mon, 14 Jun 2010 22:04:31 -0400
 "Eugene Balinski" <eugeneb at nni.com> wrote:
> 10 MHz is an industry standard.  This is goof.  However,
> you might want to consider a 1PPS GPS-trained input as
> well.   
> 
> 73,
> Gene K1NR  
> 
> On Mon, 14 Jun 2010 16:15:39 -0700
>  Wayne Burdick <n6kr at elecraft.com> wrote:
> > 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.
> > 
> > 73,
> > Wayne
> > N6KR
> > 
> >
>
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