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Path: utzoo!watmath!watnot!watdcsu!magore
From: magore@watdcsu.UUCP (M.A.Gore - ICR)
Newsgroups: sci.electronics
Subject: Re: laser communications
Message-ID: <2683@watdcsu.UUCP>
Date: Thu, 30-Oct-86 12:00:37 EST
Article-I.D.: watdcsu.2683
Posted: Thu Oct 30 12:00:37 1986
Date-Received: Fri, 31-Oct-86 03:04:34 EST
References: <2200@orca.TEK.COM> <557@hp-sdd.HP.COM>
Reply-To: magore@watdcsu.UUCP (M.A.Gore - ICR)
Distribution: na
Organization: U of Waterloo, Ontario
Lines: 25
Keywords: laser
Summary: 


	I would like to mention the Popular Electronics somewhere between
1968 to 1971 did have an article that used a power supply modulated
beam. The percentage the beam needs to be modulated need not be
great. Today a cheap way would be FSK with a fixed modulation amplitude. It
is the brightness of the laser that counts. Anyway you should be able to
get a few miles if you use FSK, a filter and some cheap optics....
You present power supply may be a problem if it is filtered. Using
a DC/DC converter could mean that you could modulate the chopping frequency
and remove the output filter. But if your DC/DC converter uses a voltage 
multiplier in the final stage you are partly out of luck using what you
have (voltage multipliers tend to be filters by design, that is the ones
that use diodes and capacitors of course).....Anyway what you *want*
is the final chopping frequency to be part of the power supply 'ripple'.
Being partly filtered would just mean that your FSK to analog transfer
would be non-linear..... Just use a good multi-polled notch filter on
your receiver.....Lots of fun....

	Good luck....
ps. Many types of lights make ***VERY*** good 60/120Hz transmitters!!! (-:
	(so watch your receiver design!... another good reason to use FSK/FM)

# Mike Gore 
# Institute for Computer Research. ( watmath!mgvax!root - at home )
# These ideas/concepts do not imply views held by the University of Waterloo.