[Laser] Re: Lunar Eclipse #3

Tue Feb 26 11:13:00 EST 2008

Hi Tim,

Very interesting text! Thanks.
This is a few point of view, which confirm of my idea, that listen of light 
pollution is impossible.

btw:  my "soon" is about two weeks.. :-)

all the best!

Robo
OM1LD

----- Original Message ----- 
From: "Tim Toast" <toasty256 at yahoo.com>
To: "laser mailinglist" <laser at mailman.qth.net>
Sent: Tuesday, February 26, 2008 9:42 AM
Subject: [Laser] Re: Lunar Eclipse #3

> 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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