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Re: Repeater on the Moon



on 4/27/03 1:29 AM, Woody at kj4so@nc.rr.com wrote:

> Like PE1RAH, William pointed out earlier today, with factual, mathematical
> data, there is a BIG difference between very weak reflections of EME signals
> from the moon's surface, and a signal from a transmitter located on the
> moon.
> 
> It will work, and we can do it, as long as we do not accept the "impossible"
> that the "experts" keep repeating every time this subject comes up.

OK, I'll jump into the fray!  :-)

While the cost and complexity of a moon system is daunting and *may* be
prohibitive, the technical aspects are not impossible to oversome.  William
and Woody are correct.

For EME, you have to consider that the moon is a passive reflector.  There
is no signal amplification at the moon.  So your signal once it leaves your
antenna and comes back to earth has at least double the path loss since
there's loss on the way up and on the way back down.  Additionally, there is
significant scattering on the face of the moon for an EME signal.  Since the
surface of the moon is rough, not all of the incident energy gets sent back
to earth.  Some of it gets reflected out into the ether of space instead.
So that increases your path loss all the more.

To the contrary with a moon type transponder.  The transponder only needs to
be able to make up on the receiving end, the path loss from the trip to the
moon.  It will then amplify the signal and send it back.  So your receiver
on earth needs only to make up the path loss of one path as well.  And since
the moon is so far away, you can use a fairly high gain antenna to hit one
half of the earth.

The other aspects of a moon based system are daunting indeed.  Impossible to
overcome?  Nope.  Will we have something someday?  Yep.  Cripe, if Amsat-DL
is going to build P5 to fly to Mars, I think the moon is certainly possible!

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/na9d   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."


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