Tacos Digest, Vol 32, Issue 8

Michael Chisena ka2zev at yahoo.com
Wed Oct 12 12:58:33 CDT 2005

If your going to broadcast with this, check out the various wireless IR headsets on the market. Been thinking of one for the office. On of the down sides of getting old is the 'music kids lisiten to today' is total crap. Then again my parents said the same thing about my favorites. That's a drag, nobody is making new classics anymore.
For not a lot of money Ramsey of all people have laser communicator kits that do this function. Some are one way, some are bi directional.
Some years ago I made a 'light radio' for one of the blind guys in my New York radio club. It was a photo transistor coupled to a small audio amp that fed a pair of walkman style headphones.
Had some fun with that.
Mulitplex LED displays (im showing my age here) made a unique sound.
Overhead lights.
Computer monitors.
At night, you can hear the filiments in auto headlights bounce as the car hits minute vibrations in the road.
I got into trouble with it too. Took it to work with me at Hazeltine and sniffed around. At that time they had a 'thick net' computer system. Seems the 'busy light' broadcast data packets that sounded just like ham packets! Security wanted to borrow my 'radio' for a few days. Then it was decided that no classified documents were on that system.
Ive used it for testing TV remotes. I suppose it could be used as a form of optach with the right test gear.
Speaking of IR, one of the things we repair here are the IR shooting scopes the troopers use after dark. We took some junk bits and peices and made us up a lab scope for testing parts and trouble shooting electronic equipment. As Ive mentioned here before these motor controlers have several boards in them. Todays repair effort was on a 'digita' board that made our test motor sing very differently than any other board we have. First I thought it was a frequency error problem, but that's not the case. Right now im looking into a different kind of noise signal on the output wave that might be dc sluging the motor. That could do it too.
I took the lab scope and observed the digital board operate today. In one corner a bunch of three terminal regulators simply glowed, they were too hot for the scope to deal with. Will need a lense or an IR ND filter of some kind to knock down the ambiant into the image converter.
Saw the heat pattern around the 8000 uProcessor, that was kind of neat. Got taken by surprise, seems a resistor network was another bright spot, I usually don't think of them as passing a lot of power. But this one was warm.
Fun in the sand.
Later dude

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Today's Topics:

1. audio over optical links as an add on to radio stations
(Samudra Haque)


Message: 1
Date: Wed, 12 Oct 2005 01:31:34 -0400
From: Samudra Haque 
Subject: audio over optical links as an add on to radio stations
To: Tacos at amrad.org

Content-Type: text/plain; charset="iso-8859-1"

Hi AMRAD folks,
What do you think of designing a circuit similiar to the last schematic
published on http://www.techlib.com/electronics/audioamps.html, I quote from
the web page:

So, what is it?

""It is a modulated light sender! Connect the input to an audio source or
microphone (a speaker will work) and the audio will amplitude modulate the
light intensity. The inefficiency of the class-A works in our favor now,
lighting the lamp to mid-brightness with no audio present. With a sensitive
detector like a phototransistor, this communicator will work several hundred
feet (at night). Best range is realized if the bulb is mounted in a typical
flashlight reflector and the detector is similarly mounted. The input
capacitor is reduced to .01 uF to give the amplifier a high-pass character
to compensate for the slow response of the bulb. The audio will sound a bit
muffled, anyway. The clever designer could use this amplifier for the
receiver, too, switching the speaker to the input for transmitting and to
the output for listening. If you choose a detector with good infrared
response, like a pin photo diode, you can add plastic IR filters to block
out ambient light and make the communicator harder to see at night.

Increasing the voltage to 12 VDC, replacing the bulb with a 3 watt, 16 ohm
speaker and replacing the .01uF with a 1uF gives an audio amp that will
deliver nearly 1 watt of audio power. The speaker will get warm, however!
(Due to the nearly 2 watts of DC power in the speaker coil.)""

I was wondering if it would be useful to build a circuit that would be
portable enough to use in a apartment or a large room or in fact put on top
of a tower/mast in a community and then fed audio from a radio/telephone
patch which would albeit slowly rebroadcast the audio in a narrow band -
without the use of actual AF or any kind of RF transmission. The
applications might be as simple as keeping the SO or XYL happy by not
rebroadcasting sounds at night, while you are trying to monitor the band -
and not using an FM transmitter to do it.

Other serious applications might be to setup a silent audio link (two-way)
between locations to connect camps together such as Burke Lake field days
with directional optical transmitter tubes (sort of point to point low power
optical links, ala lasers).

-samudra, N3RDX/S21X
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End of Tacos Digest, Vol 32, Issue 8

"You are, what you do, when it counts"
The Masso
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