I've done moon bounce. And many of these numbers seem to be not too far from Moonbounce numbers, and that is a horrid dead piece of rock reflector. that has a efficiency of a wet sponge. ...And it only reflects 6% of the energy it gets.
My guess is ... That 6% is an awful lot of power considering the 3.6 million square miles of surface doing the reflecting. Conversly, any amateur transmitter at the moon would have a much smaller receiving/transmitting antenna. Though lots more concentrated power.
So what you gain in changing from a 1/R^4 to a 1/R^2 path loss you lose a lot of it in the loss of signal receive aperture. Or something like that maybe.
Bob, WB4APR
but i would think anything there that is active circutry is a thousand times more efficient at sendinga signal back as compared to the moons surface.
2 meters downlink budged calculation:
Satellite power ................................... + 10 dBW Satellite antenna gain.......................... + 10 dBi
Satellite EIRP..................................... + 20
dBW (100 W EIRP)
2 m isotr. attenuation 400.000 km.. -188 dB
power density received on a ground isotropic 2 meters antenna..................-168 dBW
2 m ground station antenna gain.........+ 13 dBi
Power density at 2 m RX input...........- 155 dBW 2 m receiver noise floor......................- 178 dBW
Received CW signal S/N.................... + 23 dB
If we increase the BW to 2500 Hz for a SSB QSO than the
noise floor
of the receiving system increases by log (2500/500) = 7
dB i.e.
10
it becames about -171 dB and the SSB signal will be received
with a
S/N ratio = 23-7 = 16 dB wich is a very strong SSB signal.
Be aware that the above figures are based on the assumption
that the
satellite antennas are pointig toward the earth wich is not
the case with
a moon orbiting satellite.
In addition we assume that the station in QSO with you has a
70 cm
EIRP capability in order to get 10 watt from the 2m
transponder only
for you.
On the other side if a fixed 10 dBi 2 meters antenna is
placed over the
moon and it is oriented toward the earth could easily cover
the inclination
X libration window without any adjustement and only from
the point of
view of the downlink with 10 watt it can be easily used for
a transponder
on the moon.
If you make again the downlink budged calculation
considering that
the 2 meter transponder will develope only 2.5 watt for
you then you
will realize that the transponder will accomodate 3 more
stations if each
one is getting 2.5 watt as well. In this case your S/N ratio will be still +15.5 dB on CW and
+8.5 dB
in SSB and the same is true for the other 3 users.
73" de
i8CVS Domenico
Good example of path link analysis, keeping it simple!
But the trick is limiting input to four stations with a
linear
transponder and they all running an equal uplink. Reality is
this
doesn't happen so the shared portion of downlink power may
and most
likely will be less with reduced S/N. My experience with
AO-40 was
that to have a reasonably good SSB contact you needed at
least S/N of
10-dB. In fact that resulted in a fairly weak signal which
was
difficult to copy. 20-dB S/N made for arm-chair reception.
Not discussed were the 70cm uplink requirements. I suppose
one could
run high power to achieve that. My AO-40 experience was
running up
to 60w at a 16.5 dBdc antenna (18.6 dBic). Most of the time
I was
good with about 5-10w if the satellite was lightly loaded.
But with
high numbers of stations trying to operate I needed the full
EIRP =
72x60 = 4320w or in dB: 18.6 + 47.8 = 66.4 dBW
My AO-40 mode-US station consisted of a FT-847+60w linear at
the
antenna (M2-436CP42UG) for uplink. The 2.4 GHz downlink was
a
33-inch dish with helix feed+MKU-232A2 preamp+Drake
converter+FT-847
(on 123-MHz).
I'm not going to go into those calculations.
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