The whole part that is confusing me on all this power budget stuff is the to me, the seemingly HIGH budget.
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. I assume it reflects radio waves not too far efficiently than it reflects sunlight. And it only reflects 6% of the energy it gets.
I haven't found any numbers of the moos efficiency at reflecting radio signals.
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.
or what am I missing?
Joe
Edward Cole wrote:
At 05:42 AM 7/4/2008, i8cvs wrote:
----snip----
Only considering the 2 meters downlink suppose to put AO40 at 400.000 km with the antennas pointing at the earth with low squint angle let say less than 10 degrees. The gain of the AO40 2 meters antennas was 10 dBi and we put your 10 watt on it.
Suppose that your 2 meter antenna has a gain of 13 dBi and the overall noise figure of your receiving system is NF= 0,7 dB = 51 kelvin so that the noise floor into a CW passband of 500 Hz with the antenna looking at the moon (200 kelvin) is about -178 dBW
Suppose that the station in QSO with you has a 70 cm EIRP capability to get the full 2 meters 10 watt from the transponder only for you and we can calculate it later on.
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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