[Elecraft] New K3EXREF results

[Matt Zilmer]

Hi Bob,

I know for certain the the actual VFO shift is not reflected in the
REF*CAL value.  Otherwise, we'd all be seeing massive frequency error
on RX and TX.  The reference frequency is used in the DDS to derive
the injection freq, so the error should be reduced substantially by
that alone.  The ref freq is also divided down by 6 to get the 8.23MHz
2nd LO injection freq.  If Wayne's design followed others (Motorola
for one), the shift in LO and first IF would buck (cancel) each other
to some extent.

I let the K3 (#24) settle for about 2 hours this morning and watched
the REF*CAL go from .693 to .741 at present.  VFO A sitting square on
WWV 5MHz, and beat freq ran from about 2Hz at startup to 4Hz now.
Without the K3EXREF, it ran a little looser: something like 15 Hz
range top to bottom.

There's something else going on here, but would require Wayne's
analysis to clarify.  I couldn't find a schematic of the K3EXREF in
the original manual, though it's probably available.  Since the 'REF
board bolts onto the reference freq oscillator, it's probably
compensating the reference.  At least that's my take on it.  The
REF*CAL values I've seen (mine and everyone else's) are all in the
same range and no one's had any problem staying on frequency.

73,
matt W6NIA

On Sat, 29 Oct 2011 22:11:16 -0700 (PDT), you wrote:

>Hi Matt,
>
>            I'm in Ohio and waiting for the storm to pass and roads to be cleared before going back to NJ so do not have the hard data available but I ran checks too.  In my case the reference is an external Trimble Thunderbolt and I also saw shifts in the same range. Even if the first few hours are ignored, for warmup purposes, the shift was in excess of 50HZ.   Your two cases indicate 81 & 85 HZ.   If this is only the change in the reference oscillator it seems to be over the 1 PPM spec.  However I was never sure if I was accounting for all error sources in watching this oscillator correction. The +/- 2 HZ locking error at 10MHZ would be +/-10 HZ at 50MHZ alone.  I only used the values that were shown when the Trimble Thunderbolt was in disciplined mode.
>
>            Hopefully someone will comment and point out the  errors in my thinking.  Even if over the 1 PPM spec it is still the most stable and accurate receiver I've ever owned. The temperature compensation data is not being used as far as I know and I'm not close to the .5 PPM given as typical.
>
>73,
>Bob
>K2TK  ex KN2TKR (1956) & K2TKR  
>
>--- On Sat, 10/29/11, Matt Zilmer <mzilmer at verizon.net> wrote:
>
>From: Matt Zilmer <mzilmer at verizon.net>
>Subject: Re: [Elecraft] New K3EXREF results
>To: "Mark Goecke" <mgoecke at suddenlink.net>
>Cc: elecraft at mailman.qth.net
>Date: Saturday, October 29, 2011, 5:54 PM
>
>Results seem to be different for every TCXO..... 
<snip>