----- Original Message -----
From: "Bob- W7LRD" <w7...@comcast.net>
To: "STeve Andre'" <and...@msu.edu>
Cc: <amsat-bb@amsat.org>
Sent: Saturday, June 02, 2012 7:16 AM
Subject: [amsat-bb] Re: European Lunar Lander - Call for Declarations
Just for the "fun" of it I'd like to see an accurate link budget written up. It
is a little bit out of my comfort zone. Maybe Domenico or one of you who has
this knowledge could do it. I may even learn something.
73 Bob W7LRD
Hi Bob, W7LRD
Suppose to have a L/S linear transponder on the moon with the antennas
perfectly oriented toward the Earth.
L band is for the uplink from the Earth and S band is for downlink from the
Moon.
The L/S antenna gain has been selected the maximum as possible to have the
antennas main lobe pointing at the Earth despite the relative movement of the
Moon in respect of the Earth due of Libration and a fixed 20 dBi antenna on the
Moon into L/S bands could easily cover the inclination X libration window with
no need of the lunar antennas pointing correction for most of the time into a
month.
DATA FOR the 23 cm (1268 MHz) LUNAR receiving system.(UPLINK)
Noise Figure of the 23 cm lunar receiver NF = 1 dB equivalent to ( 75 kelvin )
Equivalent total Noise Temperature Te as seen by the lunar 23 cm receiver
with the antenna connected and looking at the earth..........Te = 100 kelvin
Linear Transponder 23 cm receiver Band Width................BW =150 KHz
BW: Same as in Mode-B on OSCAR-10 and in OSCAR-13
23 cm RX Noise Floor into 2.4 KHz BW and Te = 100 kelvin: KTB = -175 dBW
23 cm RX lunar transponder RHCP Helix Antenna Gain..................G = 16 dBic
23 cm TX terrestrial RHCP Helix Antenna Gain...............................G =
20 dBic
1268 MHz free space attenuation earth-moon at 380.000 Km............-206 dB
EARTH-MOON LINK BADGED CALCULATION FOR THE 23 cm UPLINK
23 cm terrestrial power =100 watt pep equivalent to...............+20 dBW
23 cm terrestrial RHCP antenna Gain........................................+20
dBic
-------------
23 cm EIRP transmitted from the earth.....................................+40
dBW
23 cm free space attenuation earth-moon 380.000 Km..........-206 dB
-------------
23 cm received power in to a 23 cm isotropic antenna
on the
moon...............................................................................-166
dBW
23 cm antenna gain connected to 23 cm lunar receiver........... +16 dBi
-------------
23 cm available power at the input of the 23 cm lunar RX ....-150 dBW (*)
23 cm lunar receiver Noise Floor in to a 2400 Hz SSB
Band Width and Equivalent Noise Temp. = 100 K ................-175 dBW
---------------
S+N/N ratio available at the lunar 23 cm receiver output......+25 dB
Now suppose that the S band 2400 MHz downlink of the lunar transponder
is 20 watt pep and that 10 earth stations are putting the same signal level
of S+N/N = +25 dB into the input of the 23 cm lunar receiver.
In this conditions the S transponder will deliver the same power to each of
the users i.e. 20 W / 10 = 2 watt pep to each user.
Now suppose that the 2400 MHz antenna of the lunar transponder is a RHCP
Helix with 20 dBic gain.
The free space attenuation of the path Moon-Earth of 380.000 km at 2400 MHz
is -212 dB
Suppose that your receiving system on the ground station is similar to that you
have used for AO40 i.e. a 120 cm parabolic dish with gain G = 27 dBic and a
2400 MHz downconverter with NF = 1 dB equivalent to 75 kelvin and performe
a Downlink Budged Calculation as follows:
MOON-EARTH LINK BADGED CALCULATION FOR 2400 MHz DOWNLINK
Power delivered for each user = 2 watt pep equivalent to .....................+
3 dBW
2400 MHz lunar TX RHCP antenna
Gain..................................................+ 20 dBic
----------------
2400 MHz EIRP transmitted from the Moon to each user.......................+ 23
dBW
2400 MHz free space attenuation Moon-Earth 380.000 Km...................-212 dB
---------------
Received power in to a 2400 MHz isotropic antenna on Earth ..............- 189
dBW
2400 MHz 120 cm parabolic antenna gain on
Earth................................+ 27 dBic
--------------
2400 MHz available power at the input of terrestrial receiver..............-
162 dBW (*)
2400 MHz Earth receiver Noise Floor in to a 2400 Hz SSB
Band Width and Equivalent Noise Temp. = 85 Kelvin (75 kelvin
for RX plus 5 kelvin for Cold Sky of the Moon = 85 kelvin )................
-175.5 dBW
---------------
S+N/N ratio available at the output of 2400 MHz ground receiver + 13.5 dB
CONCLUSION:
The above results are very close from those obtined using the calculator
suggested by jari oh3uw at the following url provided you convert my data
signed (*) from dBW to dBm
http://www.changpuak.ch/electronics/calc_10.php
A good L/S ground station of the class used for AO40 made with a 16 dBi gain
antenna on 1268 MHz with 100 watt pep at the antenna and receiving at 2400 MHz
using a 120 cm parabolic dish (27 dBi) with a Low Noise downconverter ( NF = 1
dB )
can receive from the Moon a signal with a S+N/N ratio of + 13,5 dB provided
that
the transponder on the Moon has a 23 cm receiving RHCP antenna with gain
G = 16 dBi connected to a receiver of NF = 1 dB (75 kelvin ) and a 2400 MHz
TX with 20 watt pep supplying an RHCP antenna with gain G = 20 dBic
The above characteristics are far away from those of a conventional EME
CW and SSB station and having the opportunity of a launch from ESA a
transponder on the Moon is viable in theory by all who were users of AO40
BTW the environmental conditions to get survive a transponder on the Moon
are not easy to manage particularly because of the very high change in
temperature.
I hope this helps.
73" de
i8CVS Domenico
_______________________________________________
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
