[Elecraft] [K3] KREF3 External Reference Option

[Wayne Burdick]

Prototypes are working perfectly. We're getting ready for field testing. 

Wayne
N6KR

----
http://www.elecraft.com

On Dec 22, 2010, at 4:41 PM, tsmithers at cix.co.uk (Trevor Smithers) wrote:

> Any news on the External Reference Option ?
> 
> 73
> Trevor  G0KTN
> 
> -------- Original Message  from Wayne N6KR dated 14 June 2010 --------
> 
> 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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