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Re: Communication thru P5-A



Ed, Chris and the group.   There is something wrong here in these
calculations.  The distance to the moon is 238,000 miles average or
397,000 kM.  Two way path length would be 794,000 kM.  That would
result in a 46 db less loss to the moon unless I misunderstood 
something in the original assumption. 
     If you are referring to Mars, the closest Earth/Mars distance is
usually quoted as 56 million kM.  Mars has an average distance to the
Sun of 228 million kM while the Earth 150 million kM.  Respectively,
78 kM and 378 kM would be the worse case nearest and farthest distance
depending on the oblateness of each planets orbit.  Sounds like we
better refine the path loss calculations a bit!!   Cliff K7RR

"Edward R. Cole" wrote:
> 
> Chris,
> 
> There was discussion about this a couple weeks back.  I wonder if you
> remember what the paramters are for P5A?  What freq. will be used to link
> with earth, transmitter power, antenna (gain).
> 
> With those facts we could calculate expected signal levels (i.e. path
> loss).  I need to look up the distance of Mars, but to memory it is roughly
> twice as far from the Sun, so would be on the order of 100 Million miles at
> closest approach (which only occurs about every two years).
> 
> I have a spreadsheet that calculates the path-link for eme and it is around
> 280 dB path loss at 2400!
> The formula of simple path loss is
> L = 32.4 + 20Log(Freq. in MHz) + 20Log(Distance in km)
> Lmars(min) = 32.4 + 20Log(2400) + 20Log(160,000,000)
> Lmars(min) = 32.4 + 67.6 + 164
> Lmars(min) = 264 dB
> 
> so that looks like a 16 dB stronger signal!
> 
> Now at 2304 eme stations run around 100w and a ten-foot (36 dBi) or larger
> dish!  EiRP = 400,000w
> How does this compare with the ERP of P5A?
> Lets say 10w and 20 dBi; EiRP = 1,000w
> 
> That is 1/400 the signal (-26 dB!)....hmmm 10 dB bigger dish than ten-foot
> needed (about 30-foot).
> 
> Of course I'm going on assumptions, what are the real parameters?  Anyone?
> 
> Ed, AL7EB
> 
> At 11:10 PM 8/25/2002 -0400, CLVANCIL@aol.com wrote:
> >Hi Everyone,
> >
> >At the Mars Society Convention Gary Synder (N7QAM) made a presentation on
> EME
> >as an analog for Deep Space Communication.  He said that moonbounce
> >communications is about ten times as difficult as Communications with a
> >spacecraft at Mars.  If this is true then anyone doing EME communication
> >should be able to do P5-A communication.
> >
> >--Chris Vancil
> >----
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> >
> 
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