[amsat-bb] Re: The Moon is our Future

Joe nss at mwt.net
Thu Jul 2 06:20:42 PDT 2009

MM wrote:

>Theoretically we may have a free ride to the Moon for an Amateur radio repeater!

>One theory:
>We need a simple Mode-J transponder (2-meters up, 440 down).
>Low power consumption.
>Assume minimal antenna gain from the Lander (3 dBd on each antenna)
>Assume transmitter power 5-10 watts.
Why go with the minimal antenna gain?  From the moon the whole Earth 
only displays less than 2 degrees in the sky. ( Moon shows 0.5 degrees 
from earth)
Why spill all the power where people are not?

In addition,  once the antennas are positioned,  that's more or less 
it.  There is a slight wobble (Libration) of 6.5 degrees  So  any 
antenna with a 3 db point that exceeds 6.5 degrees is just wasting 
transmitter power.

And with this link budget even an active bird that has landed and not 
flying it still will need some pretty hefty power to not need a major 
antenna setup on the earth side of the system.

Just remember what an Oscar 10 station took to have reliable 
communications,,  At Apogee it was only 35,000 miles away,  the Moon is 
almost  a ten fold increase in distance,  to keep the lander from having 
to run hundreds of watts to be heard on the earth,  ever DB of antenna 
gain will be needed for sure!


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