[Elecraft] [XV432} LO Instability Problem

[Robert Friess]

Hello Ian,

Comments below

On Fri, Jan 25, 2013 at 8:48 AM, Ian Greenshields <
ian.greenshields at gmail.com> wrote:

> Thanks for all the help and comments received so far, on and off reflector
> - I have to say the responsiveness and quality of help on this reflector is
> second to none!
>
> To summarise:
>
> 1. I have tried detuning L4, along with L3 and L5. L4 is very sensitive as
> is probably to be expected, L3 and L5 somewhat less so. The most stable
> point of L4 does seem to coincide with the peak in voltage at TP1, and
> detuning L3 and L5 doesn't seem to make much difference. The problem is
> that the voltage at TP1 can easily reach 4v or higher, and the LO
> is definitely less stable if I detune it to keep the voltage below 3v.
>
> 2. Is a voltage well above 3v at TP1 a problem? It seems to be just a
> detector diode circuit on the output of the LO, so I presume a fair amount
> of variation is to be expected.
>

This is not a problem.  You are correct there can be considerable variation
from unit to unit and crystal to crystal.


>
> 3. The crystal seems mechanically stable in that tapping it doesn't send
> the frequency all over the place, but it is highly sensitive to being
> touched, which I assume is heating effect,
>

Likely correct.  The oven will make a very large improvement


>
> 4. The biggest single improvement was a suggestion to ground the can of the
> crystal. This is something very familiar to any K2 builder. I grounded the
> crystal can, K2 filter style, to the oven -ve pad, which was the closest
> ground point. Huge improvement. The frequency jumping has gone, although
> there is still significant drift, even long after warm-up.
>
> 5. I then tried readjusting L3, L4 & L5 to see if detuning the voltage to
> about 2.5v at TP1 helped now that the oscillator seemed more stable. This
> seemed to be a backward step as the LO lurched down about 10kHz in
> frequency, started to drift back up, but then actually stopped oscillating.
> Restoring L3, L4 and L5 to the point where the voltage at TP1 peaks - about
> 4v - seems to be the most stable point & the LO starts up fine. From switch
> on it drifts about 3kHz low, then as it warms up, it starts to drift HF
> until about 3 or 4kHz above the switch-on point.
>

Tune for a peak

>
> 6. If my unit is normal, the oven would seem an essential. As I want to use
> the transverter on SSB, I can't really live with a drift range of 7kHz!
>
> 7. What is the view on grounding the crystal can? It does seem to help
> tremendously with the stability (and I mean the 'crystal mode' stability,
> just to differentiate from drift).
>

I would order a second crystal along with the oven and first try it without
grounding the can.  If it still is necessary to ground the can then do it
at the bottom near the pc board so that you can install the oven.  I would
also utilize the option to leave the oscillator and its oven on
continuously.  This option is explained in the manual.

Bob, N6CM