# [amsat-bb] Re: The Moon is our Future

Joe nss at mwt.net
Fri Jul 3 03:59:19 PDT 2009

```This is all good except for one thing,

The IF window is 10 times too small.

Look at the mess the FM single channel birds are with their tiny surface
foot print.  Imagine now a whole hemisphere worth of people trying to
use it at once.  The thing would be useless

i8cvs wrote:

>----- 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:
>>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
>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.
>
>
>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.
>
>
>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
>
>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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