[Laser] Ramsey transmit to CdS

[John Matz]

Hi
That is exactly how PWM is used ... classically.  If you truly have a PWM
light source, and the PWM sampling frequency is above 8 khz or so, usually
16 or 20 khz, then the 0-4 khz band contains an exact copy of the sampled
audio source.  The photo detector should have a BW of at least 3-4 khz for
audio.
John Matz KB9II

----- Original Message -----
From: <TWOSIG@aol.com>
To: <laser@mailman.qth.net>
Sent: Wednesday, December 03, 2003 10:30 PM
Subject: [Laser] Ramsey transmit to CdS


> I finally ran a test with my Ramsey LBC6 transmitter to the Cadmium
Sulfide
> photo sensor that I used for my laser MCW demonstration.  Both units were
hand
> held in a brightly lit room at a distance of about 30 feet.  The signal
was
> cuting out do to the beam not staying on the sensor, and the audio seemed
to
> lack the fidelity of the LBC6 receiver, but it did work.  I connected two
> batteries (3 volts) in series with the Cadmium Sulfide sensor (from a
Radio Shack
> package of miscelaneous CdS sensors) and a 2000 ohm headset (that may be
more
> than 50 years old).  No amplification, just the photo resistor varying the
> current through the headset.
>
> The CdS sensor is mounted at the focal point of a 4 inch lens (all this in
> 3.5 pound Quik container with a soup can bolted to its bottom  -  Did I
mention
> that my granddaughter likes chocolate milk? ), but for this test, I think
it
> would have worked better "barefoot".   The beam of light was only about
3/4
> inch diameter.  The difference in audio quality could be a poor frequency
> response of the light sensor, or the headset, or a false impression by me
due to the
> broken signal, maybe the ambient light.
>
> It seems to reinforce my opinion that the Ramsey PWM is being used as a
means
> of amplitude modulation, much like PWM is used to control the speed of
> electric motors.
>
> Hope all y'all had a good Thanksgiving.
>
> James
> N5GUI
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