[time-nuts] Oscillator temperature compensation
Magnus Danielson
magnus at rubidium.dyndns.org
Fri Jun 21 18:32:07 UTC 2013
On 06/21/2013 06:59 AM, Joseph Gray wrote:
>> Can you show some pictures of the oscillator?
>
> The wiring is point-to-point, so I don't think a picture is going to tell
> you much.
>
>> Is there a tunable inductor in the oscillator circuit?
>
> As I mentioned, nothing tunable there.
>
>> Who makes the unit?
>
> It is an LPB RC-6A carrier current AM transmitter. It was used at the local
> university many years ago. I was told they used to have several. I am
> rescuing it from oblivion.
The closest to a schematic I find is this:
http://i30.photobucket.com/albums/c343/1073Dave/Schematics/LPBRC-5ATransmitter.jpg
Hooking a trim-pot to either of the caps next to the crystal should
allow you to trim it, should be a good start.
If you really need temperature compensation, a first degree compensation
should help. I haven't seen anything matching the X or Y cut crystal you
most probably have. The only plot I have for an X-cut shows a mostly
linear shift. A simple trimable first degree compensation should not be
too hard.
Otherwise you might just as well lock it up instead. Divide 10 MHz down
to 20 kHz (divide by 500) and 660 kHz to 20 kHz (divide by 33) and then
a phase-comparator of choice. The varicap is just inserted under the
foot of one the caps around the crystal oscillator. Use a PI-active loop.
Cheers,
Magnus
More information about the Time-nuts_lists.febo.com
mailing list