MM wrote:
Theoretically we may have a free ride to the Moon for an Amateur radio repeater!
[snip]
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!
Joe WB9SBD