----- Original Message ----- From: "MM" ka1rrw@yahoo.com To: kg4zlb@gmail.com; amsat-bb@amsat.org; "Jack K." kd1pe.1@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