[Laser] Using a Coleman inverter for modulating fluorescent or HPS lamps

[Kerry Banke]

I purchased a Coleman 400/800 watt 12vdc to 115VAC inverter off 
a  web auction for $30 total   with the hope it could be modified to 
drive and frequency modulate light sources for our HPS and 
fluorescent light experiments. I was successful last night at rigging 
up a test setup  to run the inverter at 67.5 Hz center frequency. The 
inverter has only two ICs inside with one being the main inverter 
driver which derives its reference from an 8 MHz crystal. I used a 
signal generator coupled through a capacitor to drive the input side 
of the crystal oscillator at 9 MHz.  The next step is to replace 
the  9MHz signal generator with the VCO section of a 74HC4046 PLL IC 
and phase lock the inverter frequency to the audio output of my 
laptop.  I'll distribute the modifications after I complete the 
project shortly. The intent is to provide a fairly easy way for 
others to experiment with sending text via ordinary lamps using free 
software  which generate sequential tones in a narrow bandwidth such 
as Laserscatter, Jason, etc.  . The scheme works with most any 
incandescent, fluorescent ( without high frequency ballast) and HPS 
lamps with each type having more or less modulation efficiency.

KD0IF, K6QPV and I also completed a 25 mile two way 910 nm laser QSO 
on Wednesday of this week using PSK31. The signals were 50 dB above 
the noise in a 1 Hz BW but the PSK does not like the  very heavy 
scintillation we encountered.  We will be investigating other 
modulation approaches before we take our next step which is  45 
miles.  We have been working on our pointing techniques which are 
improving each time.  The current approach is to carefully calibrate 
the azimuth  compass rose on the tripod using the sun or a known 
distant landmark. The optics is pointed in the calculated  azimuth 
direction of the far station with a level (inclinometer) used to set 
elevation.   At 25 miles we immediately had enough signal to provide 
peaking of the receiver locally ( watching the signal on Spectrum 
Lab) and then provided audio feedback to the far site using our 
liason radio for peaking of their transmitter.
73 - Kerry N6IZW with the San Diego Microwave Group