[Elecraft] K3: REF IN

[Ian White GM3SEK]

David Pratt wrote:
>Page 17 of the K3 Owner's Manual (Rev D2) shows an SMA connector for 
>"Input for external standard frequency reference" for which a KREF3-EXT 
>option purports to be available eventually.  I understand from what has 
>been said earlier is that this will be for a 10MHz standard so you will 
>need to use the 60kHz MSF signal to lock a 10MHz TCXO or use a GPS, 
>Rubidium or Caesium standard.
>

The schematic of the KSYN3 board shows a header (J4) with connections to 
the 10MHz input, the 49.380MHz output from the existing oscillator 
module and a V_ctrl line going back to the oscillator module. This 
suggests that the KREF3-EXT module will have a phase-locked loop to lock 
the oscillator to 10MHz.

(Also on J4 is a mysterious "100Hz" bus which wanders around many other 
areas of the K3... anyone know what that is?)

However, phase locking to an external reference still doesn't mean that 
the K3 will be precisely on frequency.  Due to the internal arithmetic 
of the K3's synthesis and mixing scheme, the frequency you see on the 
display is not quite the frequency you actually get. As Wayne pointed 
out on 17 November, "this translates to a VCO step size of about 0.5 Hz 
on 160 m, 1 Hz on 20 m, and 2 Hz on 6 m. Other bands are between these 
values."

What the KREF3-EXT module should be able to deliver is complete freedom 
from frequency drift, for almost all practical purposes. There could 
also be great communication value in being able to lock a pair of K3s to 
the same global GPS standard, even when they are half a world apart

In the meantime, the K3 already has the most important kind of frequency 
and phase locking - between its own two receivers for true diversity 
reception.


-- 

73 from Ian GM3SEK