Download - Link Budget Tutorial Xx
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Link Budget Tutorial
CS 401
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Full-Duplex Communications
VHF MonopoleReceiving
VHF YagiTransmitting(Command)
UHF DipoleTransmitting
UHF YagiReceiving
Using UHF for spacecrafttransmission and VHFfor command. Most commonamateur radio modes.
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Basic HardwareCubesat Ground
Station
Transmitting Dipole Yagi
Transmitting Antenna Gain
0dB 10.2dB
Receiving Antenna
Monopole Yagi
Receiving Antenna Gain
0dB 14.15dB
Transceiver Helio-100 TS-9000
RF output Power
.5-1W 50W
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Link Budget Overview• Gains – losses• Done for both sides
– Satellite to ground station (transmit mode)– Ground station to satellite (command mode)
• Gains – Transmitter power (RF output)– Antenna
• Losses– Line loss from cable– Connector losses– Free space loss– Atmospheric loss– Ionospheric loss– System noise loss
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Decibel units
• Logarithmic unit• Ratio of power/intensity to a reference value
• P1 and P0 must measure same type and have the same units
• Solving for P1
)0
1(log10 10 P
PLdB
0101 10 PPdBL
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• dB’s are easier to add and subtract• 500mW = ? dBm• dBm = 10log10(500/1)• =10log10(500)• ~27dBm• 500mW = ? dBW• =10log10(0.5/1)• =0dBW (don’t show –dBW)
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• dB’s are easier to add and subtract• 500mW ~= 27dBm • Examples:• 10mW = 10dB• 100mW = 20dB• 1000mW = 30dB
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dB units for RF links
• dBm or dBmW – power relative to 1mWReferenced to a 50ohm load• dBc – noise or peak power relative to carrier
power• dBi – forward gain relative to a theoretical
isotropic antenna. Gain for a ½ wave dipole is 2dBi
• dBd – forward gain relative to a ½ wave dipole so gain for a ½ wave dipole is 0 dBd
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Elevation Angle• Angle between ground
station and spacecraft relative to earth
• When spacecraft is directly overhead, elevation angle is 90
• When spacecraft is on horizon, elevation angle is 0
• 0 degrees difficult to communicate, requires full line of sight. Trees, buildings, etc. may obstruct view.
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Specs required for link budget
Cubesat Ground Station
Transmitter power 500mW 50W
Antenna Gain 0dB 10.2dB
Cable length (estimate) 19cm (max) 25m
Frequency 434MHz 144MHz
Bandwidth 15000Hz 15000Hz
Modulation/BER
Altitude 800km 800km
Other specs are estimated
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Link elements
• XMTR power in Watts – RF output power• XMTR power in dBW – convert Watts to dBW• XMTR system losses in dB
-cable loss – function of frequency and length -connectors -filters -antenna mismatch – see next slide
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Antenna Mismatch• Based on VSWR ratio which will be > 1• Calculated for both GS and Spacecraft separatelyLet TX = transmitter output power, V = VSWRPL – power lossPT – power transmittedPLdB – Power loss due to mismatchThen the following are used to compute PLdB
PL = TX*((V-1)2/(V+1)2)PT = TX-PLPLdB = -10*log10(PT/TX)
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Antenna Mismatch Examples
PL = TX*((V-1)2/(V+1)2)PT = TX-PLPLdB = -10*log10(PT/TX)
Let TX = 50W and V = 1.5PL = 50((1.5-1)^2/(1.5+1)^2) =
2WPT = 48WPLdB = -10*log(48/50) =
0.18dB
Let TX = 1W and V = 2PL = 0.11WPT = 0.89WPLdB = -10*log(0.89/1) = 0.51 dB
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Link Values so farCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1
0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.35
1 - estimates
Antenna Gain – take gain of antenna and add 2dBi. Because we have no attitudecontrol, we are subtracting 3dB to account for pointing losses.Cubesat has gain of 0dB + 2dBi - 3 dB = 0dBiGS uplink antenna has gain of 10.2dB + 2.15dBi = 12.35dB – 3dB = 9.35dBi
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EIRPEffective (or equivalent)isotropically radiatedpower (EIRP)
EIRP (dBm) = Pt(dBm)– Lc(dB) + Ga (dBi),
wherePt – transmitted power (dBm)Lc – Line/cable losses (dB)Ga – Antenna Gain (dBi)
Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W)
1W 50W
XMTR Power (dBm)
0 17
XMTR System Losses (dB)1
0.5 2
XMTR Frequency (MHz)
434 144
XMTR Antenna Gain (dBi)
0 9.4
XMTR EIRP(dBm)
-0.5 24.4
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Slant Range
d – elevation angle
S -slant rangeRe – radius of the earth, 6376.136kmh – altitude of Cubesat, e.g. 800km
r = h + Re
S
Re
Earth surface
Satellite orbit
h
S = Re[{r^2/Re^2 – cos^2(d)}^1/2-sin(d)]
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Slant Range Calculations
)sin(Re*))cos*Re)(Re( 222 hS
S - slant rangeRe – radius of the earthh– mean orbital altitudeΘ – elevation angle
Use whichever formula is easiest to calculate in Excel:
)sin())(cosRe/)(Re(Re* 222 hS
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Slant Range Computations• Use Excel and compute
the slant ranges for an altitude of 325km at the elevations given on the chart.
• Use the following constants:
Re – radius of the earth = 6378.14
h – mean orbit altitude = 325km
Slant ranges for mean orbit altitudeof 800km
Elevation Slant Range
(deg) (km)
5 2784
10 2367
20 1769
30 1395
40 1159
50 1006
60 907.2
70 845.1
80 810.9
90 800
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Link Budget so far…Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5deg elevation)
2784 2784
The slant range is the same no matter which direction – from space to ground orground to space.
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Path Loss (Free Space Loss)• Path loss is a function of distance
and wavelength.• Recall that distance, i.e. the slant
range is a function of elevation• RF often refers to wavelengths
instead of frequency• Note: Cubesat transmits on UHF but
ground station transmits on VHF• Make sure that wavelength and
distance are in the same units• UHF (amateur bands)
– Frequency: 420-450MHz– Wavelength: 70cm
• VHF (amateur bands)– Frequency: 144-148MHz– Wavelength: 2m
]**4
[log*20 10 d
PathLoss
See Diallo link budget for alternative formula.
Using formula above for UHF and elevation angle of 5 degrees:
D= 2783.9 km (slant range at 5 degrees)λ = 70x10-5 (km)
Path loss = 153.97dB
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Adding Path Loss Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) 153.97 144.85
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Antenna Polarization• Linear polarization –
confines the electrical field vector to a given plane along the direction of propagation
• Circular polarization describes an electrical field that is circular over time. See URL:
• http://upload.wikimedia.org/wikipedia/commons/8/81/Circular.Polarization.Circularly.Polarized.Light_Right.Handed.Animation.305x190.255Colors.gif
Linear polarization
VerticalHorizontal
Circular polarization
Source: http://www.ccrs.nrcan.gc.ca/glossary/index_e.php?id=3089
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More Polarization Examples
Circularly polarizedRight-Hand CP
Linearly polarized(Vertical)
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Polarization Mismatches
• Antennas transmit and receive in exactly the same way.
• A vertically polarized antenna will not communicate with a horizontally polarized antenna
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Polarization Loss Factors• Given two linearly polarized
antennas rotated from each other by angle φ
• Polarization Loss Factor (PLF) = cos2φ
• If they have the same polarization, PLF = 0
• If one is vertically polarized and the other is horizontally polarized, then φ=90 and they will not communicate.
• Given a circularly polarized antenna and a linearly polarized antenna
• The LP antenna will pick up the in-phase component of the CP wave.
• So polarization mismatch will be 0.5 or -3dB no matter what angle the LP antenna is rotated to.
• Since using CP antennas (Yagis) for GS and LP (dipole and monopole) antennas on the Cubesat, PLF = 3dB
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Adding Polarization Matching LossCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (km) (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) (dB)
153.97 144.85
Polarization Matching Loss (dB)
3 3
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Atmospheric Losses• Power loss due to
absorption, refraction and scattering.
• Lower the elevation, longer the distance in the troposphere
• Major cause of signal attentuation – rain and fog
• Use a look-up table • Source: “Radiowave
Propagation in Satellite Communications” Louis J. Ippolito
ElevationAngle (deg)
Atmospheric Loss (dB)
0 10.2
5 2.1
10 1.1
30 0.4
45 0.3
90 0
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Adding Atmospheric LossesCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (km) (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) (dB)
153.97 144.85
Polarization Matching Loss (dB)
3 3
Atmospheric Losses (dB) (5 deg elev)
2.1 2.1
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Isotropic Signal at Received Antenna
• Basically gain – losses• EIRP – Losses which are
the sum of:– Path Loss– Polarization Matching
Losses – Atmospheric Losses
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Adding to Link Budget…Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
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Receiver Component
• Received signal at GS (transmit from Cubesat)
• Received signal on Cubesat (command from GS)
• Elements– Receive Antenna Gain– Receive Noise
Temperature– Receive G/T– Receive C/No– Bandwidth– Receive Eb/No– Required Receive Eb/No– Link Margin
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Receive Antenna Gain
• Receiving at Cubesat• Recall antenna gain =
0dBi
• Receiving at GS• Antenna gain = 14.15dB• Convert to dBi• =14.15dB + 2.15 dBi =
16.3dBi• Subtract 3dB for
pointing loss• =16.3-3 = 13.3dBi
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Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
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Receive Noise Temperature• Somewhat complicated• Factors include:
– Antenna Temperature/Sky Temperature
– System Line (physical) Temperature
– Noise temperature of amplifiers
– Computed feedline coefficent
– More• Will use estimates
• 377K – Receive Noise Temperature at GS
• 293K – Receive Noise Temperature at Spacecraft
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Cubesat ->Ground StationDownlink
Ground Station-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
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Receive G/T
• Receive G/T - Real measure of the receiver’s performance
• Is the “figure of merit”• Receive G/T • = Receive gain in dBi -
10 log10 ( receive noise temperature T ).
• Example• Let RG=receive antenna
gain in dBI, e.g. 13.3• Let RT = receive noise
temperature, e.g. 377• Receive G/T • =RG – 10log10(RT)
• =13.3 – 10log10(377)
• =-12.5
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Cubesat ->Ground StationDownlink
Ground Station-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
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Receive C/No (dB-Hz)• Carrier to Receiver Noise Density• C/No = Signal at Rcvr Ant + Received G/T –
Boltzmans Constant(dBW/K/Hz)• Boltzman’s constant = -228.6 dBW/K/Hz• Downlink Example:Iso. Signal at Rcvr Ant (at 5deg elevation) = -159.57Received G/T = -12.5C/No = -159.57 + (-12.5) – (-228.6) = 56.5dB-Hz
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Bandwidth
• Need to indicate bandwidth in Hz• Bandwidth – difference between upper and
lower frequency for a range of frequencies• CW < 100Hz• Bandwidth – 15000Hz – frequency range for
Cubesat and GS receivers
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Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
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Eb/N0
• Eb/N0 (the energy per bit to noise power spectral density ratio) is an important parameter in digital communication or data transmission.
• normalized signal-to-noise ratio(SNR) measure, also known as the "SNR per bit".
• No is the thermal noise density = kT , k – Boltman’s constant in Joules/Kelvin and T is in Kelvin.
• Measure of the signal-to-noise ratio for a digital communications system
• Receive Eb/N0 = C/N0 – 10log10(Bandwidth)• Required Eb/N0 is a function of the modulation scheme and
desired bit error rate (BER)
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Modulation/Demodulation Method: CUBE -Sat 2005 July 16
NOTE: Select Here: Choice Made: Result:
UPLINK:
Modulation, Coding & BER Option: 10 GMSK Eb/No:
Command Link Threshold
Option: Modulation Type: Coding: Bit Error Rate Spec: Required Eb/No (dB): 10.6
1 AFSK/FM None 1.00E-04 21.0 dB
2 AFSK/FM None 1.00E-05 23.2
3 G3RUH FSK None 1.00E-04 16.7
4 G3RUH FSK None 1.00E-05 18.0
5 Non-Coherent FSK None 1.00E-04 13.4
6 Non-Coherent FSK None 1.00E-05 13.8
7 Coherent FSK None 1.00E-04 10.5
8 Coherent FSK None 1.00E-05 11.9
9 GMSK None 1.00E-04 8.4
10 GMSK None 1.00E-05 9.6
11 BPSK None 1.00E-05 9.6
12 BPSK None 1.00E-06 10.5
13 QPSK None 1.00E-05 9.6
14 QPSK None 1.00E-06 10.5
15 BPSK Convolutional R=1/2, K=7 1.00E-06 4.8
16 BPSK Conv. R=1/2,K=7 & R.S. (255,223) 1.00E-06 2.5
17 BPSK Conv. R=1/6,K=15 & R.S. (255,223) 1.00E-07 0.8
18 User Defined None 1.00E-05 9.6
Operator Estimate of Implementation Loss
NOTE: Implementation Loss Estimate: 1.0 dB
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Required Eb/N0
• From AMSAT chart, required Eb/N0 is 9.6dB + an implementation loss of 1.0dB = 10.6dB
• Receive Eb/N0 (for elevation of 5deg)
C/N0 – 10log10(Bandwidth)
Downlink: 56.5 – 10log10(15000)Uplink: ?
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Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
Receive Eb/N0 (dB) 14.74 40.74
Required Eb/N0(dB) 10.6 10.6
Link Margin (dB) 4.14 30.14
![Page 46: Link Budget Tutorial Xx](https://reader035.vdocuments.net/reader035/viewer/2022081413/547acce7b4af9fa5158b4c1a/html5/thumbnails/46.jpg)
Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
Receive Eb/N0 (dB) 14.74 40.74
Required Eb/N0(dB) 10.6 10.6
Link Margin (dB) 4.14 30.14
![Page 47: Link Budget Tutorial Xx](https://reader035.vdocuments.net/reader035/viewer/2022081413/547acce7b4af9fa5158b4c1a/html5/thumbnails/47.jpg)
Your assignment• Complete Diallo’s link budget using Excel • Add 5, 20, 30, 45, 60 degree elevation angles for uplink• Add 10 degree elevation angle for downlink• Add formulas to compute slant ranges• Add all needed values/formulas for added elevation angles• Change the mean orbital altitude to 325km• Write a 1-page description of link budget in your own
words emphasizing the key elements. Indicate assumptions: RF power, orbital altitude, antenna gain, etc.
• Link budget due today• Paper due next Wednesday