[Laser] Retro-Reflector test

[Art]

>Wouldn't a high frequency fm-modulated carrier solve the problem? It 
>also would give you more flexibility. Perhaps you would like to 
>transmitt some tv-signals later...

No! Using an FM modulation scheme means your detector has to be 
dumbed down so that it admits the carrier frequency plus the width of 
the modulating signal (sidebands). The NEP varies (is reduced) by the 
square of the overall bandwidth-very bad!

For instance........

Say I choose NBFM and my sub carrier is at 50 Khz. I need the 
receiver to pass dc to 100 Khz. With my OOK, I need only 3 KHz 
bandwidth total. If I use the OOK as a 'reference' or baseline 
sensitivity, my 100 Khz FM system will be 33.3 times 33.3 (or 1109) 
times less sensitive! This is a 30 db worse sensitivity!!!! It 
doesn't take a rocket scientist to figure out WHY wideband and/or FM 
modulated carriers are usually used with a fiber optic link.

If you need daylight operation, it might be a viable trade off-that's 
how IR LED remote controls work (in conjunction with a visible 
wavelength reject filter).

I tried using my baycom tnc's years ago on laser. Despite the fact 
that the software was free, the modems only cost 20 dollars, they are 
powered by the computer comm port and they are very small.....the 
retries cannot be set to transmit often enough. When trying to aim 
the laser, you spend 90 percent of your time 'waiting' for the thing 
to transmit. Even though the settings are adjustable in software in 
the PC, it still is NG-the software author put limits in the software 
to prevent the thing from transmitting often enough to be useful.

No doubt this is due to the nature of the beast-when the unit is 
designed to be used on a shared channel, it should never be allowed 
to transmit constantly-or nearly constantly.

Maybe newer tnc's have over-rides?

Today we have awesome packet decoding and encoding ability available 
by using the soundcard-I'm not sure a tnc is the best answer.

Enjoy.

Art