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RE: Oscar 0



> On Thu, 22 Jun 2000, Scott E. Olitsky wrote:
> 
> > It would be interesting to do the calculations on this.  
> The path loss for
> > EME is somewhere on the order of -250 dB.  Much of this 
> loss is related to
> > the fact that the moon is a very poor reflector and only 
> 6.5% of the signal
> > that hits the moon is returned to us.  A transponder should 
> would return
> > more than that so the path loss would be significantly less.
> 
> That is forgetting one thing.  ALthough the moon is only 6% 
> effective as a
> reflector, its Antenna is several thousand square miles.  
> Your antennas on
> the moon will only be a few feet, and so they will receive 
> millionths of
> the transmitted power from earth.  If I were to guess, I 
> would say that it
> will take a 13 dB (long 2m yagi) and 1000 watts to be heard on a moon
> receiver if it only has an omni antenna (rover).  But the 
> rover then has
> to also have 1000 watts to get back, OR a larger antenna.
> 
> Good luck

Don't forget that unlike EME, where there is one path with a reflector (the
Moon) at the mid point, a transponder link is really two paths, especially
once you are able to drive the transponder to the full allotment of power
for your transmission, so the link calculations need to be done in two
halves - once for the "outbound" trip, and once for the return trip (have to
do this anyway, as the uplink and downlink will be on different bands).

So you have two paths (400000km each), no reflector loss, and antenna gain
at each end of the link.  
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