[Laser] stable audio oscillator?

[laser@mailman.qth.net]

In a message dated 4/10/03 11:46:42 PM GMT Daylight Time, flowersa@alltel.net 
writes:


> I'm building a laser communication system and I'm looking at different 
> modulation schemes for the transmitter.  I'd like to try QRSS CW--that's 
> CW in 0.5wpm or even less, using DSP to show the elements on the screen 
> using spectran or other analysis program.  I thought about keying the 
> laser on and off into a 12vdc fan to create a squarewave tone.  It works 
> fine for normal speed CW, but the frequency drift is +/- 10Hz or so. 
> For QRSS to be effective, I need rock-solid stability, preferably less 
> than 100 millihertz/min or better.  Any ideas here?  I'd like to keep it 
> cheap.  Is there some version of the 555 timer do this with good 
> components?  I was also thinking of getting some ovenized xtal thing in 
> the low RF range and then dividing down.
> 
> 

Hi.

I have designed my system to be used with QRSS, but so far the system 
performance has been so good I haven't needed to resort to QRSS (ARGO 132)

The requirement is just to make sure that the oscillator is very stable, so 
you know where to look on the QRSS screen.

A simple solution is to use a crystal and divide down. If you have an audio 
filter on the receive end then tansmitting squarewaves is perfectly OK.

The circuit for a 4060 and a 4MHz crystal is on my web site and has been used 
successfully for a couple of years. The 4060 needs the crystal 2 capacitors 
and a 10M resistor for the oscillator section. Output on mine is 488Hz.  
With QRSS is VERY important to select a modulating frequency that avoids 
multiples of 50Hz (Europe) or 60Hz in the USA.

www.g0mrf.freeserve.co.uk/laser.htm

73

David


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