[Laser] Sky illumination experiment

[wa4qal at ix.netcom.com]

> Message: 4
> Date: Tue, 5 Jul 2005 18:20:08 EDT
> From: TWOSIG at aol.com
> Subject: Re: [Laser] Sky illumination experiment
> To: laser at mailman.qth.net
> Message-ID: <191.42a5b73e.2ffc6198 at aol.com>
> Content-Type: text/plain; charset="US-ASCII"
> 
> 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  
> control the no signal (and max) current.  Then adjust the audio amp for the  way you 
> would for a two tone test.  If you could get your hands on a plate  modulated 
> transmitter, just remove the modulator and use the output of the plate  
> modulation transformer to drive the light........   Hmmmmm.  you  might need a 
> little bias current through the  transformer.........    Now this stuff is getting 
> too old for  me.

That might work, although there are some complexifying items to consider,
such as supplying heater voltage to the fluorescent tube (You might be
able to use some of the no heater fluorescent tubes, although some of these
are rather slow to start, and some require an inductive high voltage kick to
get started).  Additionally, you have to make sure that the tube never 
drops out due to low current on the modulation peaks, since they don't
restart very well.  The ambient temperature needs to be considered, too,
since too low of an ambient temperature can cause them to drop out
(Condenses the mercury vapour in them?).  There's also the minor problem
of ion migration if you use them on DC, so you need to have a way to 
periodically reverse the current flowing through them.  Excessive currents
may result in ion bombardment issues of the filament, which may cause 
sputtering and darkening of the tube ends.

> What about taking an AM signal from a transmitter through an antenna  coupler 
> (tuner) to drive the light?  Adjust the drive for the amount of  power you 
> need.  If you have to, put the rf across a bridge diode, to drive  the light 
> with modulated DC.

Actually, AC might be better, due to ion migration problems.

> Not elegant, but probably less work than modifying a inverter.    

Oh, I don't know about that.  Inverters can be pretty simple.

> You could 
> even build the RF to DC conversion circuit in a metal bucket ( ala  "Cantenna" 
> ) to shield it from leaking RF and harmonics.  

Why not just excite the light with the RF, and then stick a metal screen 
around the fluorescent tube to shield the RF from escaping?

> Hope the suggestion was worth thinking about.
>  
> James
>  
> N5GUI

Dave
WA4QAL