[Laser] another lunar experiment
F1AVYopto at aol.com
F1AVYopto at aol.com
Fri May 9 06:38:52 EDT 2008
>To compare that with my xenon strobe
>transmitter, I am pushing the small tube to its limits to
>get barely 3 kw peak and 3 watts average power to hit the
>moon.
>Which one would have the strongest signal i wonder??
>1 killowatt CW vs. 3 kilowatts in pulses, assuming the
>mirror is 100% modulated at the same frequency as the
>strobe (10 Hz say)??
Tim
The most important is the energy you transmit and proportionally you receive.
If you use the FREQUENCY DOMAIN to detect your signal by FFTDSP, a one kW
average power (square signal modulated at 50% duty cycle) will be incomparably
better your 3 kW peak 3 watts average power to hit the moon.
Many reasons for that:
The number of photons you will receive is in the energy ratio by time unit.
To be sensitive the FREQUENCY DOMAIN FFTDSP must accumulate in high
resolution during long time.
T duration short pulses must be amplified in a 1/2T bandwidth that means
enormous extra noise.
A short time low rate pulsed signal gives very numerous harmonic frequencies.
With the FFTDSP FREQUENCY DOMAIN the harmonic FFTDSP spectral lines will be
very weak because the energy is divided in each of them.
To detect low rate short pulses, you must use a TIME DOMAIN receiver with
ultra high accuracy synchronic time window, adapted filters, correlation,
convolution... many complex electronic processes.
For example an ultra short pulse can be detected via an APD in Geiger mode
which is over biased just at the expected arrival pulse time and during the
same duration the pulse width.
It needs very accurate and difficult time controls....
73 Yves F1AVY
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