[Laser] Question: PSK31 with inverter modulating fluorescent

[TWOSIG at aol.com]

Kerry
 
>From your posting "...Coleman inverter for modulating fluorescent ...", I  
have a question about how it would work with PSK.  It is a result of  confusing 
two different parts of your post.  I was thinking that you had  done PSK by 
phase locking a 9 MHz VCO signal generator to the audio output of a  laptop.  
Perhaps a better way to say it is that a 9 MHz VCO is  controled by the error 
voltage from a phase detector which compares  the divide by N of the inverter 
circuit to the audio output from a laptop  programmed to send PSK.  What I was 
going to ask was how much frequency  deviation did the VCO experience?  And how 
long did it take for the  VCO to "settle down" to its stable frequency?
 
I can see that BPSK could be generated by the phase loop, but it would seem  
to have unusual charateristics if compared to the PSK normally used on HF.   
First it would have constant amplitude and each cycle would be a step change in 
 phase instead of the "Normal to RF for minimum bandwidth" constant phase  
with amplitude change with phase reversal at minimum  amplitude.  The laptop 
audio would have a dead zone of low amplitude  between phase changes, too weak to 
drive the phase detector, which would cause a  delay starting the phase 
change.  That delay added to the time required to  relock the loop, could be as 
much as the bit time.  If so wouldn't that be  a potential to cause bit errors in 
the system.  That said, wouldn't the  system work better if the audio output 
frequency were much higher than the 67.5  Hz I have assumed for your system ( 
a system designed to work at 60 Hz with an 8  MHz oscillator that you are 
driving at 9 MHz ).  
 
Finally, I am having some trouble imagining the complications in the  system. 
 If you were trying to drive a florescent bulb with a 67.5 Hz  signal with 
phase reversals, you seem to get pulses at 135 Hz, and a 180 degree  phase shift 
at 67.5 Hz gives you a 360 degree, and therefore undetectable, phase  shift 
at 135 Hz.  To make the system work, you would need to tap into the  inverter 
divide chain at double the output frequency.  It might be easier  to put a 
photo detector near the light source and apply that to the phase  detector. 
 
It may be just my limited imagination, but it seems to me that a multi-tone  
system would cause the phase lock loop to have phase detector output spikes 
that  would try to drive the VCO hard to its limits when the tone changes, but 
still  could not make "crisp" frequency changes.  That may not be a problem for 
 the detection circuitry, but if you were to listen to it, the sound would be 
 "sliding" from note to note.
 
Hence my questions about how much the VCO will deviate on a phase or tone  
change, and how much time to settle.
 
 
James
N5GUI