[amsat-bb] Re: NASA's American Student Moon Orbiter...

[Edward Cole]

At 05:44 PM 7/3/2008, G0MRF at aol.com wrote:
>
>In a message dated 04/07/2008 01:16:33 GMT Standard Time,
>domenico.i8cvs at 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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73, Ed - KL7UW              BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 185w
http://www.kl7uw.com     AK VHF-Up Group
NA Rep. for DUBUS: dubususa at hotmail.com
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