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Re: Oscar 0



"Scott E. Olitsky" wrote (in part):

> Bob did raise a good point which I had neglected.
>
>  Although the moon is a very poor reflector, it does capture a large amount
> of the signal as it spreads out from earth.  The moon's diameter is about
> 3475 km.  If you assume a 100% "reflection" from the transponder with a dish
> antenna with a surface area of 2m instead of the moon's diameter, the
> pathloss would  be about -365 dB, much greater than the EME pathloss at 144
> mhz.  The improvement in reflection adds about 11dB of gain but the decrease
> in size adds about 124 dB of loss from the equations that I have seen.
> Obviously the transponder would have to amplify the signal as well.

No kidding!  I don't know where several people discussing this have gotten the
idea that a transponder on the moon would have "100% reflection" (or zero gain -
or loss) through it.  I don't really know what the OSCAR satellites have for
gain, but any active repeater has gain - LOTS OF IT!  I did grab out my 1994
ARRL handbook which has a fairly decent set of numbers for calculating link
budgets for OSCAR-13, and it comes out to just over 150dB (that's not a typo -
that One Hundred Fifty dB) of gain through the transponder.  It is reasonable to
assume that a transponder on the moon could have somewhere around that much as
well.  Due to the path losses, I would not ever expect to be able to have
handheld coverage using a transponder on the moon, but it should not be all that
difficult to get it within the reach of a high end AO-10 class station.

73
-----------------------
Jim Walls - K6CCC
k6ccc@amsat.org
http://home.earthlink.net/~k6ccc/
626-302-8515    FAX  626-302-9999


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