[amsat-bb] Re: Phase 4 versus Eagle

[Edward Cole]

Have to agree with Drew even if this reduces signal levels at extreme 
latitudes.  I would assume that the P4 centered on the NA&SA would 
boresight the equator with a beam chosen to match the earth's 
apparent angular size = arcsin (8000/23500) = 19.9 deg. which 
corresponds with an antenna with 19.5 dB.  At 2.4 GHz an 18-inch dish 
has about 19.7 dB gain.  Such a footprint would only be 3 dB down at the poles.

I would guess that at 145 and 435 MHz the satellite antennas will not 
be large enough to produce 20 dB* of gain, so only a percentage of 
their signal will hit earth with a larger amount radiating uselessly 
into space.  The reverse issue for the satellite Rx antenna; only a 
small percent of the beam will see earth signals.  This means mode UV 
(old Mode-B) will require larger ground station 
antennas.  Calculating this is straight forward path-link 
calculations.  One can plug in the range and Tx power (say 50w) and 
receiver sensitivity (-145 dBm) to come up with antenna gain requirements.
No I will not do that for you this time - hint I have a calculator on 
my webpage that a clever person could modify - check out
Mar's Reconnaissance Orbiter (MRO) Radio Test at the bottom of:

  http://www.kl7uw.com/raseti.htm

How does the range to Geostationary orbit compare with apogee on 
AO-13 or AO-40?  I think you will find that a standard AO-13 mode-B 
antenna system will be adequate (depending on the power and antennas on P4).

73 Ed - KL7UW
*Note:  on 144 MHz my eme array produces 21.3 dBi gain  (a bit large 
to install on a satellite)

At 12:00 PM 12/14/2007, Andrew Glasbrenner wrote:



>>Probably a good pointing spot would be where XM and Sirius Point their
>>antennas - just about on the Canadian Border close to Winnipeg- Manitoba
>>73
>>Robin VE3FRH.
>
>Probably not if we care about covering the Southern Hemisphere. We 
>really don't know enough even to speculate, but this likely won't be 
>a spot beam like the Ku and C band transponders use. Range will be 
>less than AO-40, so the earth is a fairly big target still.
>
>73, Drew KO4MA

73,
Ed - KL7UW
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