[Elecraft] Temp Compensation cct adjustment

Thu Mar 11 12:13:00 2004

Hello Ron,
    In all my "spare time", I want to do the same thing. My L31 is as yours
was, but the mods here produced an noted improvement oover the unmodified
PLL oscillator. It drifted down about 10-12 Hz over a 15 minute keydown
period at 3 watts out. The heat rise was not that horrendous, so I am sure
it can be made better. The hair dryer would sure speed things up!
    Years ago, I had a homebrew ssb filter rig with an FET 5 MHz vfo. I
temperature compensated it over the space of about a month while I worked in
a calibration lab. I would run it once a day and adjust the room air
conditioner or heater to radically change the ambient temp of the vfo. I
plotted the temperature and freq drift. (HP5245L counter). I found that
after soldering anything in the circuit, I had to wait many hours for the
soldering heat to dissipate from the affected parts! (I did one run per day)
It was slow work, but in the end, I had the VFO drift down under 20 Hz from
a cold turn on! It was awesome.
    If anyone plays around with the resistor change, I would allow some time
for the solder heat to dissipate before trying a new run.  Maybe an hour or
two minimum.

73
Dave K1WHS   K2 #1247  #915
----- Original Message -----
From: "Ron ZL1TW" <[email protected]>
To: <[email protected]>
Sent: Thursday, March 11, 2004 8:51 AM
Subject: [Elecraft] Temp Compensation cct adjustment


> Hi ,
>           In an earlier posting I admitted to being somewhat disappointed
> with the Temperature compensation circuit, and it wasn't until a thread
> about the PLL range having to be a lot smaller than I had mine for it to
> work properly, that I realized what my problem was.
> In my K2 , changing L31 back to 10uH reduced my PLL range from 24.89Khz to
> 10.64kHz ,(YMMV),and at that stage the drift of my rig was considerably
better.
> However, after a bit of correspondence with it's designer, ( John KI6WX) I
> was encouraged to have a go at "fine tuning" the circuit to minimize drift
> further.
> This procedure is outlined at the end of the Installation Instructions for
> the kit, and involves changing the value of one resistor ( RA) and is a
> relatively simple operation. The hardest part, if you have the DSP or KAF2
> installed is the removal of the filter, and the Control board, to be able
> to get to resistor "RA" which is installed parallel on the top of the
> Temperature compensation board.
> It was a simple matter from there to heat each end of the resistor with
the
> iron and gently remove it, one end at a time.
> Replacement is simple and doesn't require cleaning the holes out. I just
> shaped the legs of the resistor I was trying and cut them short, then
> heated each end and slid the legs into the holes. A wee touch of solder
and
> it was all done.
> My next step may raise a few eyebrows, but I then reassembled the radio
> except for the KPA100, and *GENTLY*  heated the inside of the set with the
> XYL's hair dryer while monitoring WWV  with the "spot" tone activated.
That
> gave me a *ROUGH* idea of how the circuit was working with that value
resistor.
> After a few subsitutions I ended up using a 39k resistor for "RA".
> I re-installed the KPA100 and did tests with the set being driven into a
> dummy load to apply the heat this time.
> The results were most gratifying.
>   After allowing for a small amount of drift after initial boot-up, the
set
> will now drift down about 10hz when the PA is heated to the point where
the
> fan comes on, which is heaps better than it ever has been. Subsequent
> cooling and heating produced the same results.
>   To finish the job, I used Wayne N6KR's method to set C22, and am pretty
> confident that my K2 is now calibrated about as accurate as I will ever
get it.
> 73......Ron ZL1TW      ( cu EQP ?)
>
>
> --- StripMime Report -- processed MIME parts ---
> multipart/alternative
>   text/plain (text body -- kept)
>   text/html
> The reason this message is shown is because the post was in HTML
> or had an attachment.  Attachments are not allowed.  To learn how
> to post in Plain-Text go to: http://www.expita.com/nomime.html  ---
> _______________________________________________
> Elecraft mailing list: [email protected]
> You must be subscribed to post to the list.
> To subscribe or unsubscribe see:
http://mailman.qth.net/mailman/listinfo/elecraft
> Elecraft Web Page: http://www.elecraft.com
> Also see: http://www.elecraft.com/elecraft_list_guidelines.htm
>
>