[amsat-bb] Re: The Moon is our Future
i8cvs
domenico.i8cvs at tin.it
Thu Jul 2 21:31:18 PDT 2009
----- Original Message -----
From: "MM" <ka1rrw at yahoo.com>
To: <kg4zlb at gmail.com>; <amsat-bb at amsat.org>; "Jack K." <kd1pe.1 at gmail.com>
Sent: Thursday, July 02, 2009 1:31 PM
Subject: [amsat-bb] The Moon is our Future
> We need a simple Mode-J transponder (2-meters up, 440 down).
> Low power consumption.
> Assume minimal antenna gain from the Lander (3 dBd on each antenna)
> Assume transmitter power 5-10 watts.
>
> Questions:
> What’s the link budget?
> How much gain will be needed on earth for such a setup?
> Can we build a working mockup in 1 year or less.
>
> The Moon is within Reach. Let’s Go for IT.
>
> Miles WF1F MarexMG.org
Hi Miles, WF1F
The gain of the 2 meters antenna on the Lander is 3 dBd = 5.14 dBi
Assume that the Noise Figure of the 2 meter receiver is 0.5 dB = 35 kelvin
and the sky temperature as seen by the 2 meter Lander antenna looking at
the earth is conservatively 290 kelvin but (probably more ).
The isotropic path loss earth-moon in 2 meters at an average distance of
380.000 km is 187 dB
You don't specify the IF bandwidth of your transponder so that for
simplicity I will assume that only one QSO will be possible in SSB and 3
on CW in a total BW = 2.5 KHz
With the above data the calculated Noise Floor (KTB) of the above 2 meter
Lander receiver is -139 dBm
We assume to use an earth 2 meters antenna with a gain of 13 dBi and a power
of 100 watt pep in 2 meters.
UPLINK BUDGED:
Earth TX power 100 watt.............................+ 50 dBm
Earth antenna gain............................. .............+ 13 dB
------
Earth EIRP.....................................................+ 63 dBm
2 m isotropic attenuation earth-moon..............-187 dB
------
Isoptropic power received on the moon .........- 124 dBm
2 meters Lander antenna gain.........................+ 5 dBi
------
Power applied to the 2 m Lander receiver......- 119 dBm
Lander receiver 2 m Noise Floor...................- 139 dBm
------
S/N ratio available from the Lander receiver.. + 20 dB
COMMENT:
With a 2 meter signal +20 dB above the noise floor the
70 cm TX on the Lander transponder is in condition to
supply a noise-less power between 5 to 10 watt pep to
the 70 cm TX antenna.
DOWNLINK BUDGED:
The gain of the 70 cm antenna on the Lander is 3 dBd = 5.14 dBi
and the 70 cm power is 10 watt pep
Assume that the Noise Figure of the 70 cm earth receiver is
0.5 dB = 35 kelvin and the sky temperature as seen by the 70 cm
antenna looking at the moon is 75 kelvin
Assume that the antenna gain of the 70 cm earth receiver is 18 dBi
The isotropic path loss earth-moon in 70 cm at an average distance of
380.000 km is 197 dB
With the above data the calculated Noise Floor (KTB) of the 70 cm
ground receiver is -144 dBm
Lander 70 cm TX power 10 watt...................+ 40 dBm
Lander antenna gain.......................................+ 5 dBi
------
70 cm EIRP from the moon...........................+ 45 dBm
70 cm moon-earth isotropic attenuation .........-197 dB
------
70 cm power available in to isotropic antenna -152 dBm
70 cm earth receiving antenna gain..................+ 18 dBi
------
70 cm power on input of the earth receiver.....-134 dBm
70 cm Noise Floor of the earth receiver..........-144 dBm
------
S/N ratio at the output of 70 cm receiver.......+ 10 dB
COMMENT:
Using a Lander transponder on the moon with 2 meters and
70 cm antenna's gain in the order of 5 dBi will not produce
serious problems of pointing at the earth due of libration.
If the Lander transponder is capable to develope 10 watt
pep and the IF bandwidth is very narrow in the order of
2.5 KHz it is possible to accomodate one SSB QSO or 3 CW
QSO just using the actually available TX and RX equipments for
satellite communications i.e.
For the uplink in 2 meters 100 watt pep and a 13 dBi antenna gain
For the downlink in 70 cm a receiving system with an overall Noise
Figure of 0.5 dB and antenna gain of 18 dBi
The rate of change of the frequency due of doppler shift in 2 meters
and 70 cm is very slow and easily manually compensated even into
only a 2.5 KHz bandwidth
The antenna polarization is very important because a linear signal
transmitted from the earth or from the moon by stations located in
different continents can be reversed from Vertical to Horizontal
polarization so that at least on the earth circular RHCP and LHCP
switchable polarization is recommended.
Best 73" de
i8CVS Domenico
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