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From: henkp@nikhefk.UUCP
Newsgroups: sci.electronics,sci.physics
Subject: Re: Laser eavesdropping
Message-ID: <133@nikhefk.UUCP>
Date: Fri, 3-Apr-87 12:24:28 EST
Article-I.D.: nikhefk.133
Posted: Fri Apr  3 12:24:28 1987
Date-Received: Sun, 5-Apr-87 05:49:28 EST
References: <499@sw1e.UUCP> <15260@onfcanim.UUCP> <2628@phri.UUCP>
Reply-To: henkp@nikhefk.UUCP (Henk Peek)
Organization: Nikhef-K, Amsterdam (the Netherlands).
Lines: 13
Keywords: modulation
Xref: utgpu sci.electronics:455 sci.physics:1033

In article <2628@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>In article <15260@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
->	If you want to get fancy, you can modulate the beam as it leaves
->the laser and put the signal output of the photoreceptor through a bandpass
->filter centered on this frequency (this will mask out incident light); now
->the voice signal will appear as AM modulation on top of the carrier you
->originally used to modulate the beam with.

The voice signal appear as phase modulation on modulation frequention
of the laser. A "phase multiplier" like mc1496 and a phase shifter
to put it in the linear region does the detection job.

Henk Peek, ..!seismo!mcvax!nikhefk!henkp.UUCP