[Laser] moon repeater

Mon, 15 Dec 2003 20:22:36 -0500

If I remember correctly from a conversation I had with PGP, he thought 
he might have detected his echo with about 500mw of IR and LF 
modulation, but we are talking about very long-term averaging.  Any kind 
of doppler effect should be insignificant--wavelength at 20Hz is around 
15000 km.  The biggest problem is likely the light from the moon.  Even 
a new moon is quite "bright" to a sensitive receiver.  Perhaps a very 
narrow filter for 780nm would be in order.  BTW, if anyone is going to 
try this, keep in mind that you'll have to pause every 2.5 seconds to 
listen for your echo--your own backscatter off the atmosphere will be 
MUCH stronger.  

I'm taking my LF tx/rx pairs back to Nebraska this week.  I might get a 
chance to play with some troposcatter stuff if the wx cooperates and I 
can convince N0RHL to man the other station  I'll have to figure out how 
to pack it in the suitcase.  I'll probably dissassemble quite a bit of 
the gear, especially the tunifish can assembly.  I imagine those would 
look pretty scary on the xray machine. :-)

Andy K0SM/2

[email protected] wrote:

>In a message dated 12/15/03 9:32:00 PM GMT Standard Time, [email protected] 
>writes:
>
>>I was wondering if anyone has tried using the Apollo
>>retroreflectors with low power lasers in combination
>>with the 20 hz QRSS type modulation? Since that seems
>>to be the cutting edge of weak signal tech these days.
>>Even though it would only be usefull for hearing your
>>own signals i suppose.
>>
>>
>
>This could be a very good idea. 
>I have used slow CW to make many QSOs on the LF bands ( 73kHz and 136kHz) and 
>it's a technique that works well.
>I guess some further questions would be:
>1) Over what distance on the earths surface would the reflected laser be 
>visible?
>I'm not at all sure of what happens to the divergence of a laser after it 
>encounters a retroreflector?
>2) although we can modulate audio onto the laser by chopping it with an 
>accurate source what happens with doppler as the relative distance changes? I guess 
>that the carrier changes wavelength but does the modulation? Possibly it does 
>too, which would be a problem for very narrow bandwidth reception.
>
>Probably still need a few Watts.
>
>73
>
>David   G0MRF
>
>
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