© Electronic Systems Laboratory 1999
by Buchan Milne
WWW:sunsat.ee.sun.ac.za
The Sunsat imager downlink was planned to give real time downlinking of areas close to Stellenbosch. At the University, we have a 4.5m diameter dish which we are modifying to include a LEO tracking capability. There are larger professional quality ground stations elsewhere in SA that can extend the communications slant range beyond the 1700km assumed for Stellenbosch.The imager bit rate (and receiver noise bandwidth) is adjusted to maintain square pixels at the various orbit heights. Apogee and perigee cases are given below.
Sunsat's transmitter antenna is a 2-turn RHCP helix. Assume Tx gain = 0dBi to allow for cable and mispointing losses.
For elavation = 30 degrees, Range = 2 * altitude
For 30 degrees elevation and 850km altitude, 33Mbit/s
Diam_metres = 4.5, GHz = 2.25, Eta = 0.6, ===> Dish ant gain =38.29 dB_i
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Inputs
Carrier frequency GHz = 2.25
Range km = 1700
Transmitter dBm dBm = 37
Transmitter gain dBi = 0
Receiving gain dBi = 38.29
Total noise temp, ant+cables+rx Kelvins = 100
Receiver G/T dBi = 18.29
Receiver IF bandwidth Hz = 3.3e+007
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Received power dBm = -88.8
Microvolts into 50 Ohms uV = 8.115
Equivalent input noise power dBm = -103.4
IF Signal to noise ratio dB = 14.61
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For 30 degrees elevation and 520km altitude, 60Mbit/s
Diam_metres = 4.5, GHz = 2.25, Eta = 0.6, ===> Dish ant gain =38.29 dB_i
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Inputs
Carrier frequency GHz = 2.25
Range km = 1040
Transmitter dBm dBm = 37
Transmitter gain dBi = 0
Receiving gain dBi = 38.29
Total noise temp, ant+cables+rx Kelvins = 100
Receiver G/T dBi = 18.29
Receiver IF bandwidth Hz = 6e+007
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Received power dBm = -84.54
Microvolts into 50 Ohms uV = 13.26
Equivalent input noise power dBm = -100.8
IF Signal to noise ratio dB = 16.28
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For 5 degrees elevation and 850km altitude, 3Mbit/s
Diam_metres = 4.5, GHz = 2.25, Eta = 0.6, ===> Dish ant gain =38.29 dB_i
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Inputs
Carrier frequency GHz = 2.25
Range km = 2400
Transmitter dBm dBm = 37
Transmitter gain dBi = 0
Receiving gain dBi = 38.29
Total noise temp, ant+cables+rx Kelvins = 100
Receiver G/T dBi = 18.29
Receiver IF bandwidth Hz = 3e+006
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Received power dBm = -91.8
Microvolts into 50 Ohms uV = 5.748
Equivalent input noise power dBm = -113.8
IF Signal to noise ratio dB = 22.03
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Sunsat 435 Mhz downlink
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Inputs
Carrier frequency GHz = 0.435
Range km = 2400
Transmitter dBm dBm = 40
Transmitter gain dBi = 0
Receiving gain dBi = 0
Total noise temp, ant+cables+rx Kelvins = 300
Receiver G/T dBi = -24.77
Receiver IF bandwidth Hz = 1.5e+004
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Received power dBm = -112.8
Microvolts into 50 Ohms uV = 0.5113
Equivalent input noise power dBm = -132.1
IF Signal to noise ratio dB = 19.25
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Sunsat 145 Mhz downlink
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Inputs
Carrier frequency GHz = 0.145
Range km = 2400
Transmitter dBm dBm = 36
Transmitter gain dBi = 0
Receiving gain dBi = 0
Total noise temp, ant+cables+rx Kelvins = 1000
Receiver G/T dBi = -30
Receiver IF bandwidth Hz = 1.5e+004
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Received power dBm = -107.3
Microvolts into 50 Ohms uV = 0.9679
Equivalent input noise power dBm = -126.8
IF Signal to noise ratio dB = 19.57
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