[Laser] Re: Lunar Eclipse #3

[Tim Toast]

here are some of the numbers without crunching them too
much:

speed of light 299792.4 km/second

wavelength of 120 Hz = 2498.27 km 
wavelength of 360 Hz = 832.75 km 
wavelength of 100 Hz = 2997.92 km 
wavelength of 300 Hz = 999.30 km 

radius of moon 1738 km
radius of earth 6378 km

TOF 1738 km = 5.7973 x 10-3 seconds (5.7973 milliseconds)
TOF 6378 km = 2.1274 x 10-2 seconds (21.274 milliseconds)

pulse of 5.7973 ms = half cycle of 86.247 Hz sinewave
pulse of 21.274 ms = half cycle of 23.502 Hz sinewave
pulse of 1.0000 ms = half cycle of 500 Hz sinewave

length of 1 ms pulse = 299.79 km

While pondering things, one thing that struck me was this
broadening of a pulse by the reflection off the curved
surface of the moon. And this is also assuming you are
illuminating the whole surface of the moon (0.5 degree beam
or larger). The moon's radius of 1738 km seems to lead to a
minimum pulse length of 5.79 milliseconds regardless of how
short the initial pulse was.

So, if you are using the entire visible surface of the moon
on your photodiode, any pulse reflected back to you will be
5.79 milliseconds long plus the initial pulse length. Is
this correct?

For example, if you send a 1 millisecond pulse, the
reflection would be 5.79 + 1.000 or 6.79 ms long. I assume
this is some sort of constant well known to the RF moon
bouncers, and is related to the fastest modulation that can
be sent without being garbled by the pulse lengthening that
occurs with wide FOV's.

This 5.79 ms pulse length can also be thought of as equal
to a frequency of 86.247 Hz. The 5.79 ms pulse in this case
represents a half cycle of a sinewave of 86.247 Hz
frequency.

How this relates to the frequencies of 120 Hz or 100 Hz i'm
not sure. Would modulations above 86 Hz be diminished when
using the entire moon on your photodiode? 

If your FOV is LESS than the entire hemisphere of the moon,
then it seems like higher modulation frequencies would be
OK. There's probably a formula for how the pulse
lengthening relates to field of view. But it seems like,
the smaller your field of view, the higher the frequency
you can see (ungarbled by pulse lengthening).

I was thinking, if your field of view is half the moon's
surface (0.25 degrees), then you might have twice the
modulation resolution. Meaning instead of 5.79 ms pulses,
you would have 2.895 ms reflected pulses and 172 Hz
bandwidth capability. Does this sound like it could be
correct? I'm sure this translates badly, sorry.

A picture is worth a thousand words 8)

This concept of circular bands of light moving from center
to limb was mentioned in here before but i'm not sure who
brought it up.... Anyway, imagine a single light pulse sent
toward the moon. When the resulting plane wave front
arrives, it strikes near the center portion of the moon
first. Then radiates in a circular pattern outward toward
the edges (limb). The time it takes to go from the center
to the limb is about 5.79 milliseconds. (TOF of Moon's
radius)
If you send out pulses at a rate of one every 5.79
milliseconds, then just as one pulse has radiated outward
to the edge, another one starts at the center and moves
outward. If you space out the pulses to about twice this or
11.58 ms, then you have a nice 50/50 duty cycle pulse train
being reflected back to you from the moon. That is the
86.247 Hz signal that appears to be an upper limit for
undistorted modulation when using the entire moon's surface
on the photodiode.

I hope this calls to attention anything that might be of
value for anyone pondering these problems.


------------------------------------

>I need more  time for this, and I need 
>paint two pictures for ilustration of  situation.
>I hope, that my teory evoke interesting  discussion.
>shortly:
>1. wavelenght of 120Hz is 2500km! after  phaseshift of
3phase powerline is 
>833km!
>2 Diferent between short  and long way of bounced light is
minimal 4800km!
>3. Lamp is powered from  long distance from few electric
power station 
>....this is next phase  shift.
>4. more milions sources of different phase!
>5. phase shift  of 120Hz earth surface lamp is interlaced
up to DC level.
>Is it any wrong  at this?
Robo


...
>With the  synchronic networks, the chaotic light sources
>repartition could
>build some  beats with by constructive or deconstructive
>adding’s.
>This effect could  create circular interferences from the
>heath and moon
>curvatures.
>It is  possible a fraction of percent of modulation can
>occur in favourable
>circumstances.
>The city light pollution is equivalent to hundreds
>megawatts  optical power.
>The FFTDSP are so sensitive it seems to me something could
>be  detected in
>very favourable circumstances.
...
>73 Yves F1AVY






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