[Laser] Sky illumination experiment

[John Matz]

Hi
If I remember correctly, flourescent lights, that is, gas discharge tubes,
have a negative resistance ... their current would increase very much if
they didn't have a ballast in series with the tube.  But they are fast
enough for audio modulation.  The problem with incandescent bulbs is the
time constant ... they are sloooow to light up and dim down ... which means
they are hard to modulate.  Also their resistance is very low when cold but
reasonable when hot ... which makes them hard to match too.  In either case,
I think you want to have the light lit to half brilliance or so (bias) and
put modulation as current in series.  This may be very possible using an
appropriate transformer as a step-up from a multiwatt audio source in series
with the bulb, a dropping resistor (or ballast resistor) and a dc source
(rectified and filtered ac line).
... just my two cents ...
John Matz KB9II
----- Original Message -----
From: "Kerry Banke" <kbanke at qualcomm.com>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Tuesday, July 05, 2005 5:43 PM
Subject: Re: [Laser] Sky illumination experiment


> I hadn't thought about the RF excited tube approach. Haven't done that in
> many years. I don't know if I even have enough TX power available on any
> band to really light up two 40w bulbs.  I suspect we would could go a lot
> further with the RF leakage that with the light scatter unless the bulbs
> were  RF shielded as well:) Interesting thought though. There are always a
> number of ways to get the job done depending on what equipment is most
> easily available.
>   - Kerry N6IZW -
>
> At 03:20 PM 7/5/2005, you wrote:
> >At first I was going to suggest that a tube type transmitter, AM / CW
might
> >be cheaper and easier to modify to drive the florescent light.  With
> >a  screen
> >modulated transmitter just quench the oscillator and put in a bias to
>
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