Re: Mars (was: Miles Per Watt Trials)

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From: Kevin Purcell (xenolith@halcyon.com)
Date: Sat Mar 04 1995 - 18:27:12 EST


>If there is somebody listening at the other end, such communication is
>well within the capability of EME-capable stations.
>
>Given a distance of 2.7*10**8 km (this is the 20th century, folks -
>miles have been obsolete for ages), the free-space path loss is 263 dB
>at 1.3 GHz, and 281 dB at 10 GHz - about the same as EME. It *is* a
>lot further, but the Moon is a lousy reflector, adding many dB to the
>loss. The path losses will be less at opposition, of course.
>
>To do this at QRP power levels is improbable, unless you have *lots*
>(>60 dB) of antenna gain. This could very easily start another round
>of transmitter output power vs. ERP arguments... :-)
>
>Interplanetary probes use QRP-ish power levels, but NASA and Co. can
>spend a lot more money on their receivers and antennas than any of us
>can.
>
>73 from Burnaby,
>laura VE7LDH

They also use transmission systems that can look for very low S/N (probably
negative) and have massive error correction e.g. Galileo's low gain antenna
is sending data at 10 bits per second as it heads toward jupiter ... thats
about 12 wpm :-)

Kevin Purcell, N7WIM // work: kevinpu@atm.com // home: xenolith@halcyon.com
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