[Laser] Another TX+RX system coming to life

[Paolo Cravero]

Hello,
more than a year after I've made my first post on this reflector I have 
finally managed to assemble an MCW TX, RX is on the way.

Nothing hi-tech, but hopefully a starting point for some fun.

My TX currently uses a 10mm clear case red LED driven at 10mA average, 488 Hz 
MCW carrier.

The RX is a OPT202 with additional 3M3 series resistor to reduce the device 
bandwidth, soon to be followed by a bandpass active filter.

I have achieved a copy of the signal through ceiling reflection; feeding the 
OPT202 output to the MIC input of a laptop running Spectran (but it was 
audible too). No focusing lens was used. Total distance: about 6m ("Personal 
Best", HI).

A few of questions.

If I add a second LED in series rather than dissipating heat in the 
controlling resistor, I double the output power, don't I? Provided the current 
flowing is unchanged.

Using several LEDs rather than one will not affect the radiation pattern, as 
occurs with Yagi antennas at RF, right? (I'm pretty sure about this one.)

Why do many people seem to use Fresnel lenses? Can't I use a el cheapo 
magnifying lens from the china shop around the corner? It's just a weight matter?

What are your DX experiences /without/ a lens in front of the detector? 
Probably with a laser rather than a LED...

I will soon need a LOS wireless voice intercom that should work over a 
distance of about 300m. Would this work with a LED as TX in a urban 
environment? Fewer accurate beaming requirements and no risk to beam a laser 
into someone's eyes. Any circuit to recommend?

Cloud bounce. I read about K3PGP's experiments and others: were they carried 
in rural areas or are there some chances in big cities as well?


Thank you for your attention and your time,
Paolo IK1ZYW

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