[Laser] Sky illumination experiment

[TWOSIG at aol.com]

Hmmmmmm.   A few comments in reply.
 
Somebody check me on this, but a florescent tube, is a simple gas discharge  
tube, the significant fact is that the gas inside radiates in the ultraviolet  
range (unlike the neon bulb which has a visible spectrum emission) which then 
 activates a coating on the inside of the bulb which glows visible light when 
 exposed to UV.  The heaters are used to reduce the trigger voltage and are  
not required if you have the voltage to fire the tube.  
 
Yes there is negative resistance, that is the sustaining voltage is lower  
than the firing voltage.  For lighting, you need ballast to limit the  current 
flow.  If you are designing a control circuit ( vacuum tubes or  whatever) to 
modulate the light output, then the ballast function ( current  limiting ) 
needs to be in the included in the control, not added on to make the  light work.
 
I don't think mercury vapor is used in common lamps.  If I remember  
correctly it is just low pressure oxygen, about the same pressure as a neon  indicator 
bulb.
 
An HF transceiver coupled to an RF impedance transformation device (antenna  
tuner) should drive a florescent tube very easily.  Modulation needs to be  CW 
or AM.  The tube will respond to the power output, not any changes in  
frequency.  FSK input to the transceiver will give steady light  output.  My head is 
too fog brained right now to figure out what QPSK or  BPSK will do, but I 
suspect that if you cannot receive intelligible signals from  an receiver in AM 
mode, then the modulation technique is wrong for this light  experiment.  That 
being said, I am sure that there are ways  to computer generate the correct 
output for  digital communication on an SSB transceiver, it just may not be the  
same as are used now for HF radio communications.  As noted before, RF  
radiation will likely be a problem, but can be handled. 
 
 
Incandescent bulbs, low power, should work as an infrared source for low  
frequency modulation techniques.  The more powerful the bulb's rating, the  more 
thermal mass it will have.  Think of the thermal mass as a low pass  filter.  
Best way to find out what they will do is to wire some up and  experiment.  
(Should be worth an article in an experimenter's  magazine.)   I have seen some 
decorative bulbs with very  thin, long, filaments.  These should work better 
than an  equivalent power rated bulb with thick coiled filament.  Also, the  
experiment should indicate if they are better sources with the filament not  
glowing, glowing dull red, bright red, yellow, or white hot.  They might  work 
better as IR sources at lower temperature, they might not.  If the  white light 
from a hot filament is "noise" then the best S/N ratio might be in  between.
 
 
 
James
N5GUI