[Laser] Depth of modulation for various lamp types

[Kerry Banke]

As part of the experiment in communicating using fluorescent and HPS 
lamps, I am interested in which lamps have the greatest depth of 
modulation. I assume that the combined total lumen output along with 
the depth of modulation pretty much determines which lamp type will 
produce the greatest useable signal. I ran a very crude experiment 
last night on a 150W HPS,  a two  48" bulb fluorescent fixture and a 
400w halogen work lamp.  I just used a pin photo diode connected to 
an oscilloscope set in DC couple mode as the detector. I picked a 
peak signal level that seemed to indicate the greatest modulation 
with the fluorescent lamp and used that same light intensity for the 
other lamps for comparison.  The HPS is great with at least 80% 
modulation and a nice half wave rectified looking waveform. The 
fluorescent looked to be about 50% with a very non-symmetrical 
waveform, and the Halogen lamp had maybe 10% modulation using this 
method.  I guess though the bottom line is most any lamp type could 
be used to experiment with this type of power frequency 
modulation.  As part of the test I did transmit and receive text 
with  each of these lamps using the Jason software set for a center 
frequency of 135 Hz.  Does anyone know of some published data on 
depth of modulation for various lamp types? Weather permitting ( fog 
& haze a problem sometimes) we plan to try copying various light 
sources as a beacons at 20+ miles later this week.   Stay tuned.
73 - Kerry N6IZW -