[Laser] EME Experiment

[f1avy at yahoo.fr]

Hello Mike,
Some details about this experiment...
The K3PGP photo detector acts in fact like a charge sensitive amplifier.
It is the FET drain gate capacitance amplified by the Miller effect that integrates the noise in medium audio frequency .
The rising front of the signal could be rather fast (less than 20 microseconds) but the loaded capacitance restore its charge during a long time (tens off milliseconds). 
So the pulse is very enlarged and the time of correlation to add and average is not very critical (may be +/- 2 mS).
A simple high pass filter presize the pulse shape before averaging and contributes to reject lot of 1/F noise. 
To use a pulsed mode with a K3PGP RX, the pulse rate must not be well over 20/s...even with a low capacitance PIN photodiode.
To teleload the report file try :
http://dl1u.savefile.com/4f6d0b36153eed056af74610b64bd491/Report.pdf
73 
Yves F1AVY
http://f1avyopto.wifeo.com

--- En date de : Mar 16.6.09, kd7ts <kd7ts at aceweb.com> a écrit :

> De: kd7ts <kd7ts at aceweb.com>
> Objet: Re: [Laser] EME Experiment
> À: "Free Space LASER Communications" <laser at mailman.qth.net>
> Date: Mardi 16 Juin 2009, 15h15
> Hi Tim,
> 
> Sounds like a great experiment. I understand long term
> integration using RF. This simply uses the difference of non
> coherent noise and coherent signal to average the noise and
> signal over time
> 
> In the case of the light pulse, it seems to me, the
> frequency is not the interesting data, but rather the
> timing. If this is true, I have serious reservations
> concerning the softwares ability to provide the desired
> performance. I have no successful experience with timing to
> this level of accuracy, but I do know that X86 based
> processors and the PC clock are pretty poor performers
> concerning time.  Wolf provides some "work arounds" in
> the Spectrum Lab program, but I am not sure this is what's
> needed. 
> 
> I followed your link(s) but all I saw was an ad server.
> 
> Interesting details would be soundcard model, sampling
> rate, operating system and PC processor speed. 
> 
> I think the process could be simulated with a delay driving
> an LED locally to see if the concept performs to your
> expectations. Possibly, this has already been explored.
> 
> Ernie (W7LHL) and I experimented with bistatic radar on 24
> GHz to measure reflections and quickly found the software
> timing problem to be insurmountable using available hardware
> and software.
> 
> At any rate, this sounds like a very interesting
> experiment. Thanks for sharing your experiences.
> 
> Mike KD7TS
> 
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