[time-nuts] Oscillator temperature compensation

Max Robinson max at maxsmusicplace.com
Fri Jun 21 21:55:41 EDT 2013

In my opinion you are expecting more of the transmitter than it was designed 
to give.  A carrier current transmitter wouldn't have to maintain the 
broadcast standard of plus or minus 20 Hz.  A drift of 200 Hz would never 
have been noticed on an all American five radio.  Given a strong received 
signal beats with other stations on the same channel wouldn't be an issue 


Max.  K 4 O DS.

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----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: <time-nuts at febo.com>
Sent: Friday, June 21, 2013 1:32 PM
Subject: Re: [time-nuts] Oscillator temperature compensation

> 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
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