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Re: Oscar 0



It would be interesting to do the calculations on this.  The path loss for
EME is somewhere on the order of -250 dB.  Much of this loss is related to
the fact that the moon is a very poor reflector and only 6.5% of the signal
that hits the moon is returned to us.  A transponder should would return
more than that so the path loss would be significantly less.  I had worked a
couple of very large stations with my satellite antenna and 300 watts.  With
an extra 11dB of gain in a new amplifier and antenna system I can hear my
own echos fairly often.  If you assume that the transponder had the ability
to return 100% of the signal that it hears (i.e. "reflects 100% rather that
6.5%) The loss would decrease by that same 11 dB.  A ham using a single long
boom yagi and a small amplifier, should be able to hear a CW signal
returning from the moon fairly often.  A huge antenna array like those used
in EME would not be needed.

Scott

AC3A
-----Original Message-----
From: Dan Schultz <n8fgv@AMSAT.Org>
To: amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
Date: Wednesday, June 21, 2000 11:45 PM
Subject: Re: [amsat-bb] Oscar 0


>I think it is very intriguing to put an amateur transponder on the moon,
>but before we
>get started let's do the link margin calculations. The moon is very very
>far away and
>most hams will not be able to work a lunar transponder with an HT and an
>arrow
>antenna. Only those "elite" hams with big antenna arrays in their
>non-covenant
>restricted backyards will be able to work a repeater on the moon, and
>once it is
>deployed there we will no doubt see postings on amsat-bb about how
>"Amsat builds satellites for the elite minority and not for the average
>ham."  So lets make sure that
>everybody understands this up front.
>
>I think that before this mission happens they will need to find
>additional sponsors
>besides Radio Shack. Nevertheless it can't hurt for us to start
>designing some sort of
>transponder if they are interested in carrying it. They may be more
>interested in
>selling content to internet sites than in carrying a package of interest
>only to ham
>radio operators, and only to an elite group of hams at that. But it
>canít hurt to ask.
>
>With the passing of Werner Haas, Amsat has lost more than half of its
>linear
>transponder design knowledge. Werner designed and built most of the
>communications payload for AO-10, AO-13 and Phase 3D. I frankly don't
>know
>who is going to step forward to fill those shoes. I don't know of anyone
>in the
>USA who has built a linear transponder in the past two (or is it three)
>decades and
>there is precious little published literature on the subject.  Most of
>the people who built Phase 3D have let it be known that this will be
>their last satellite, but most of the technical knowledge behind P3D is
>locked away in secret file cabinets. I don't know where the next
>generation of satellite and transponder builders is going to learn these
>arcane skills. The crew that built Stensat made a good effort in a very
>short time but they did not have the benefit of any prior experience in
>building a satellite,  The requirements are much harder than simply
>building a piece of gear for your ham
>shack.
>
>So in spite of all these problems, please count me in if there is such a
>project. Iíve been trying to design a linear transponder for a balloon
>flight in my copious free time but Iím afraid it hasnít gotten very far
>along.
>
>Dan Schultz N8FGV
>
>
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>

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