[Laser] Re: pulsed laser

[F1AVYopto at aol.com]

Tim
 
At a lower  rate than about 8 pulses/second the PGP RX has an abnormal 
sensitivity due to a  strange parametric effect.
The floating internal photodiode capacitance  unloads at each pulse into the 
photodiode itself. At the same time at each pulse  the vr decreases before 
reloading.
During this capacitor unload its C value  increases! (hyperbolic Cd versus Vr 
curve)
So the voltage variations goes  down in abrupt decreasing pulses very faster 
than for a fix  capacitor. 
This effect  disappears above about 8 pulses/second because the photodiode 
does not fully  recharge its own capacitance and the normal 1/2piRC effect 
begins to  act.
During our 40 Km cloud bounce laser test with F8DO we used a dancing  
stroboscope for clouds beaconing that could be adjusted from 1 pulse/second to  20 
pulses/second at constant power.
I have a "Wave Pad" picture and a sound  file that shoes this effect at 40 Km.
I can send them in direct mail if you  want.
73  Yves.