At 05:44 PM 7/3/2008, G0MRF@aol.com wrote:
In a message dated 04/07/2008 01:16:33 GMT Standard Time, domenico.i8cvs@tin.it writes:
Hi Ed, KL7UW
If we put AO40 at a distance of 400.000 km instead of 60.000 km from the earth the increase of isotropic attenuation at 2400 MHz is about 16 dB etc etc etc.........
Hi Ed / Dom
On the other hand, if you were to reduce path loss by using 70cm as the uplink band and 2m as the downlink the numbers begin to look quite possible.
Also, if the satellite is orbiting the moon, then it's quite likely that the attitude will be such that the experimental end of the satellite is pointing at the moons surface. This probably also means that the communication antennas are not pointing at the earth, so high gain will not be possible. Maybe 3 or 4dB is the limit.
So how about 10W of 2m on the satellite and a passband that's say 5kHz wide? Not good for SSB, but passable for CW or reasonable speed coherent BPSK
Regards
David
David,
I think you meant to say 5-Hz vs 5-KHz bandwidth. That is one of the best ways to improve the link equation and CW or WSJT will work well.
When you lower isotropic path loss by lowering frequency, keeping the same antenna gain means much bigger antennas. The footprint on a Moon orbiter would be probably too small to get enough gain on 2m or 70cm.
But this exercise of using AO-40 as a benchmark has its limits. One should just do the complete pathlink analysis to come up with good numbers. The one factor that is always there is a big jump in pathloss due to 400,000 km vs. earth orbit.
Ed I have a pathlink excell calculator on my website for MRO that can be modified to work for a lunar orbiter. http://www.kl7uw.com/raseti.htm
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