2007:089
M A S T E R ' S T H E S I S
Design, Development and Operation of a Student Ground Station
Anura Wickramanayake
Luleå University of Technology Master's thesis
Space Science
Department of Space Science, Kiruna
Design, Development and Operation of a Student Ground Station
A.B.A.T Wickramanayake
June 2007
ABSTRACT
Design, Development and Operation of a student ground station is a Master thesis project done at the Department of Space Science (IRV), Luleå University of Technology, Sweden. The Objective of this degree project is to develop and operate the IRV student ground station that operates within amateur radio bands (VHF and UHF). Hardware and software were selected after studying the existing student ground stations. Tokyo University CubeSat XI-IV, CUTE-1 and XI-V were used for testing of the uplink and downlink performance. Those experiments gave good results for Ax.25 packets and for CW signals. Handover experiments were carried out to determine the importance of the IRV ground station in a possible student ground station network. The results showed that IRV ground station has a unique advantage due to its location. SWR measurements were carried out for VHF and UHF antenna systems that gave results below 2. It is observed that noise levels due to external electromagnetic interferences in amateur radio bands are negligible. Currently the IRV ground station is fully functional in VHF and UHF bands and has the option of expanding to S band
INDEX
ABSTRACT... i
INDEX ... ii
LIST OF FIGURES ... v
LIST OF TABLES... vii
CHAPTER 1 ... 1
INTRODUCTION ... 1
CHAPTER 2 ... 3
GROUND STATION TECHNOLOGY ... 3
Hardware... 4
Software ... 4
People... 5
Operations... 5
Decoding ratio... 7
Student Ground Stations and Student Satellites... 7
Comparison of Student Ground Station Technology... 9
Hardware... 9
Software ... 11
Hardware selection... 12
Software selection... 13
Cost of finance ... 14
Antenna theory... 15
Polarization ... 15
Standing Wave Ratio (SWR)... 16
Antenna bandwidth ... 17
Impedance... 17
Directivity of the antenna and antenna beamwidth... 17
Radiation Pattern... 18
Gain of the antenna ... 18
Omnidirectional antennas ... 18
Yagi antennas... 20
Digital communication... 22
Link Budget ... 23
Link margin... 23
Calculation of (C/N)ach... 24
Equation needed to calculate the (C/N)req for detail link budget ... 25
Receiver figure of merit... 26
Losses... 26
Global Educational Network for Satellite Operation (GENSO)... 31
CHAPTER 3 ... 33
IRV GROUND STATION STATUS ... 33
Ground station specification ... 33
Description of used hardware and software... 35
Tower and antennas ... 35
Transceivers ... 35
Rotor and rotor controller ... 36
Preamplifiers... 37
Radio Computer Interface... 38
Rotor Computer Interface ... 38
Power controller switch ... 39
The UEK-200SAT receive converter ... 39
Power supply... 40
SWR & Power meter ... 41
Audio Noise Reduction filter... 42
Cables... 42
Connection of hardware... 43
Software setup... 44
Pre-pass software ... 44
Real time software ... 44
Past-pass software... 44
Operational Procedure ... 45
CHAPTER 4 ... 46
IRV GROUND STATION PERFORMANCE ANALYSIS ... 46
Preliminary link budget ... 46
CUTE-1 FM operation to find out the decoding ratio of IRV ground station ... 51
XI-IV FM operation to find overall data download ratio ... 52
Interference monitoring ... 54
Testing of the SWR for the antenna systems ... 54
CHAPTER 5 ... 55
DISCUSSION AND FUTURE WORK... 55
CHAPTER 6 ... 57
CONCLUSION... 57
CHAPTER 7 ... 58
REFERENCE... 58
APPENDIX 1: Detail specification of hardware ... 60
ICOM IC-910H Specifications ... 60
General... 60
Transmitter... 60
Receiver ... 61
Audio Noise Reduction Filter ... 62
Cable specifications ... 63
APPENDIX 2: Glossary ... 67
LIST OF FIGURES
Figure 01: Relationship between Space segment, Ground system and Data users... 3
Figure 02: A block diagram of a basic ground station... 5
Figure 03: Picture of a student ground station (LTU ground station)... 7
Figure 04: Picture of a student satellite... 7
Figure 05: E-field variation of Linear and Circular polarization... 15
Figure 06: Definition of antenna beamwidth ... 17
Figure 06: Omnidirectional antenna (Discone type)... 18
Figure 07: Discone antenna elevation radiation patterns for 145 MHz ... 19
Figure 08: Discone antenna elevation radiation patterns for 145 MHz ... 19
Figure 09: Skeleton slot fed Yagi antenna... 20
Figure 10: Cross Yagi antenna... 21
Figure 11: Voltage polar diagram and gain against VSWR for Yagi antennas ... 21
Figure 12: Worst case distance between the satellite and the ground station... 25
Figure 13: Clear sky radio signal attenuation due to oxygen and water vapour in the atmosphere ... 26
Figure 14: Galactic and tropospheric noise temperatures at various ground antenna elevations (δ)... 27
Figure 15: Ground station receiver noise... 28
Figure 16: Attenuation Lrain and noise temperature due to rainfall at 30 deg elevation above the local horizon ... 29
Figure 17: UHF/VHF Yagi antennas ... 35
Figure 18: Picture of the ICOM IC-910H transceiver ... 36
Figure 19: Rotor and Rotor controller ... 36
Figure 20: AG-25/AG-35 preamplifier... 37
Figure 21: ARR GaAsFET Preamplifier... 37
Figure 22: ICOM CT-17 Radio Computer Interface ... 38
Figure 23: GS-232B Rotor Computer Interface... 38
Figure 24: Power controller switch... 39
Figure 25: UEK-200SAT receive converter ... 39
Figure 26: Kenwood PS-52 Power supply... 40
Figure 27: SAGA 300 Power supply ... 40
Figure 28: SWR & Power meter (1.8 – 150 MHz) ... 41
Figure 29: SWR & Power meter (140 -450 MHz)... 41
Figure 30: Audio Noise Reduction filter ... 42
Figure 31: Hardware connection... 43
Figure 32: Plot of time stamps of decoded packet at each ground station... 51
Figure 33: Comparison of downloaded data at each pass... 52
Figure 34: The integration of obtained data at each operation time. ... 53
Figure 35: The ratio of obtained data at each ground station ... 53
LIST OF TABLES
Table 1: Satellites Modes... 6
Table 2: Hardware comparison with other Universities ... 10
Table 3: Software comparison with other Universities... 11
Table 4: Hardware Selection... 12
Table 5: Software selection... 13
Table 6: Cost of finance as at 2006... 14
Table 7: IRV ground station specifications ... 34
Table 8: Preliminary downlink budget for 70 cm antenna ... 47
Table 9: Preliminary downlink budget for 2 m antenna ... 48
Table 10: Preliminary uplink budget for 70 cm antenna ... 49
Table 11: Preliminary uplink budget for 2 m antenna ... 50
CHAPTER 1
INTRODUCTION
The Objective of this degree project is to develop and operate the IRV student ground station that operates within amateur radio bands (VHF and UHF). IRV ground station was first established in 1990’s but since 1996 it has not been functional due to the lack of experience staff (for operations and maintenance) and due to the out-of-date instruments.
In 2006, Dr Priya Fernando (senior lecturer at IRV and Project manager, Ground Station Project) started the Ground Station Project to re-establish the IRV Ground Station with the aid of European Union Development fund. During this degree project, the IRV ground station build from scratch to its current fully functional state. This degree project was carried out under the supervision of Dr. Priya Fernando. In this thesis the chapter 2 is about the ground station technology related to student ground stations and it covers hardware and software comparison and selection, antenna theory and link calculation etc.
The chapter 3 is about the IRV ground station status and it covers the detail description of used hardware and software, hardware and software setup, operational procedure etc. The chapter 4 is about the IRV ground station performance analysis and it covers the preliminary link calculations and the results of the experiments. Chapter 5 is the discussion and future work and chapter 6 is the conclusion. Owing to its location in the northern hemisphere at a latitude of 67.7 degree north, the IRV ground station at Kiruna has the great advantage of having more passes for polar satellites. Secondly, the ground station is located at a considerably flat area with very low population around, so almost no interference from electromagnetic disturbances or blocking from high rise buildings, giving it a very good contact at even low elevations. With the plan of launch of its Cubesat by IRV, it’s very important to have an operational ground station. Till the Cubesat project is launched, a considerable experience in satellite communication and operation can be achieved by working on this ground station. after comparing the existing student ground stations, “CUE DEE 15X 144” VHF antenna, “CUE DEE 17 X 432” UHF antenna, “YAESU 5400B” rotor controller, “ICOM 910H” transceiver, “AG-35” and
“AG-25” preamplifiers ,“Nowa for Windows” software, “Winorbit” software, “GMS
(Ground Station Management Service)” software, “Packet Engine Pro” a software based TNC (Terminal Node Controller), terminal program (AGWTERMINAL), “Hamscope”
software and “CWget” software are selected for the project. Tokyo University Cubesat XI-IV, CUTE-1 and XI-V were used for testing of the uplink and downlink performance and obtain good results for Ax.25 packets and for CW signals. During the experiments it is observed that packet downloading and decoding can be done at very low elevation angles like 5-degrees and also found that the ground station has a data decoding rate around 40% (48.25 % CUTE-1 and 32.1% for the XI-IV). Handover experiments were carried out to determine the importance of the IRV ground station in a student ground station network. From these experiments showed that the IRV ground station has a high data downloading capacity for polar satellites (twice as university of Tokyo). SWR measurements were carried out for VHF and UHF antenna systems and both measurements are below 2. Noise levels in amateur radio bands are negligible due to external electromagnetic interferences. The preliminary link calculation shows that IRV ground station can receive the telemetry of a satellite which has a minimum EIRP of -19 dB in 70 cm or -28 dB in 2m band. Also it can upload telecommand to a satellite which has an antenna with a minimum gain of -267 dB in 70 cm band or – 275 dB in 2 m band.
Currently the IRV ground station is fully functional in VHF and UHF bands.
CHAPTER 2
GROUND STATION TECHNOLOGY
A ground station is an earth-based point of communication with the spacecraft/Space segment. They are the source for our interaction with the satellites; hence play an important part for any satellite related operation and it is very important to have a good communication link between the ground station and the satellite/space segment. Usually a ground segment/ground system involves following tasks. (Ref 6, page 477)
• Tracking and determine the position of the satellite orbit
• Telemetry operations to acquire and record satellite data and status
• Commanding operations to interrogate and control the various functions of the satellite
• Controlling operations to determine orbital parameters, to schedule all satellite passes and to monitor and load the on-board computer
• Data processing operations to present all the engineering and scientific data in the formats required for the successful progress of the mission
• Voice and data links to other worldwide ground stations and processing centres
Figure 01: Relationship between Space segment, Ground system and Data users.
Data Relay
Spacecraft and payload support
Ground System
Command and tracking data
Telemetry
Mission Data
Figure 01 shows the relationship between space segment ground segment/ground system and data users (Ref 5, page 623). Normally a ground segment can be divided in to 4 main components. (Ref 6, page 477)
• Hardware
• Software
• People
• Operations Hardware
Basically the hardware section consists of antennas, rotors, transceivers, computers, power supplies, peripherals, data recorders etc.
Software
There are mainly 3 different kinds of software uses in the student ground station operations
• Pre-pass software
• Real time software
• Post-pass software
(Normally in a commercial ground station there are 4 different kids of software involves, including the onboard software which needed for the space craft. At present most of the student satellites does not have the function to upgrade onboard software using the uplink from the ground station. Therefore the onboard software is not an essential item in a student ground station.)
Pre-pass software
The software which is required in advance of the pass of the spacecraft to
• Determination and prediction of the orbit
• Observation planning and scheduling
• Command list generation and simulation.
Real time software
The software which is required during the spacecraft is visible to the ground station. This include the antenna tracking software, computer control software, command and data handling software etc
Post-pass software
Post-pass software are the software that needs for Housekeeping, quality control and health assessment, data processing and orbit determination and for data analysis.
People
In a commercial ground station people are involved in many different areas of responsibilities such as site and project management, operation shift staff, hardware staff, software staff, data and engineering support staff, administration, specialist engineers and scientists. However in a student ground station all the operations are carried out by few staff members and couple of students.
Operations
This brings hardware, software and people together. The operations team is the fundamental human unit that integrates the mission software and hardware into on effective routine process.
Figure 02: A block diagram of a basic ground station
Ref 06
For a ground station to operate successfully with a satellite, the communication equipments should be in compatible with the selected satellite modes. The satellites modes are the combination of uplink frequency, downlink frequency, and transmission modes. Table 01 shows a list of common satellite modes. (Ref 14)
Mode Description
A This mode requires a 2 meter SSB/CW transmitter and a 10 meter SSB/CW receiver and supports CW and voice.
B This mode requires a 70 cm SSB/CW transmitter and a 2 meter SSB/CW receiver and supports CW and voice. Some satellites also support RTTY and SSTV in this mode.
K This mode requires a 15 meter SSB/CW transmitter and a 10 meter SSB/CW receiver and supports CW and voice. This mode is unique in that it can be done with a simple HF rig.
JA This mode stands for J Analog and requires a 2 meter SSB/CW transmitter and a 70 cm SSB/CW receiver and supports CW, voice.
JD This mode stands for J Digital and requires a 2 meter FM transmitter and a 70 cm SSB/CW receiver and supports packet.
S This mode requires a 70 cm SSB/CW transmitter and a 2.4 GHz SSB/CW receiver and supports CW and voice.
T This mode requires a 15 meter SSB/CW transmitter and a 2 meter SSB/CW receiver and supports CW and voice.
Table 1: Satellites Modes
Some satellites have dual modes that operate simultaneously. For example, AO-13 (Amsat Oscar 13) (Ref 14) can operate in mode BS which means that it can operate in both modes B and mode S simultaneously. Other common dual modes are KT and KA.
Decoding ratio
Ground station decoding ratio is defined as the ratio of decoded packets in the ground station to packets sent from the satellite. Packets sent from a satellite are estimated from duration of pass time and the interval of packet output. The interval of packet output is a property of the satellite.
Student Ground Stations and Student Satellites
Figure 03: Picture of a student ground station (LTU ground station)
The student ground stations (Ref 11-16) are mainly design to communicate with student satellites. Most of the universities have their own satellite programs to give experience to the students about the design of satellites. Most of these satellites are weighing less than 5 kg and communicate via UHF and VHF bands using Ax.25 packets (communication protocol).(Ref 4- page 256, Ref 8) Cubesat (a small satellite of 10 x 10 x 10 cm cube and weigh less than one kg ) is a popular satellite program among the universities (Ref 12).
Figure 04: Picture of a student satellite Ref 16
Currently there are number of student satellites in orbit. Tokyo University XI-IV, XI-V, CUTE-1(Ref 15), California Polytechnic State University (CalPoly) CP-3, CP-4 (Ref 16) are some examples. Since most of the student satellites communicate via the UHF/ VHF amateur radio bands, the minimum requirement of a student ground station is the ability to communicate via UHF/VHF amateur radio bands. But, some universities are developing satellites which can communicate via S band (Ref 15), so in the future student ground stations may need the equipments to communicate via S band as well.
Comparison of Student Ground Station Technology Hardware
Hardware University of Tokyo , Japan (Ref 15)
California
Polytechnic State University , USA
(Ref 16)
JMUW, Germany
(Ref 10)
Tower • Creative Design
CR-30
• Rohn JRM23810
• JRM23810
• Hummel Teletower Jumbo III Antenna 1 (2m -VHF) • x213 : VHF
(Creative Design)
NDA • M2 2MCP22
Antenna 2 (70 cm -
UHF) • x727 : UHF
(Creative Design)
• M-squared 436CP42
• M2
436CP42U/G Antenna Rotor • Elevation Rotator
ERC5A (Creative Design)
• Azimuth Rotator RC5A-3
(Creative Design)
• Yaesu G-5500 • Yaesu G-5500
Rotor controller NDA • Yaesu G-5500
controller
Yaeau G-5500 controller Rotor computer
interface • Yurin (Original control system use PIC)
• GS-232B • WinRotor
Rotor computer
interface driver • RS-232 NDA • WinRotor XP
Transceiver • IC-910D (ICOM) • Yaesu 847
• ICOM IC-910H
• ICOM
IC-910H Preamplifier 1 ( for
VHF) • AG-25 NDA • LNA-145,
SLN Series Preamplifier 2 ( for
UHF) • AG-35 • SP-7000 • LNA-145,
SLN Series Radio computer
interface • CT 17 • CT-17 NDA
Radio computer
interface driver • RS-232 CI-V interface
NDA NDA
Power controller switch • Original hardware High power Solid State Relay (OMRON)and relay interface system (RBIO series/Kyoritsu RBIO-4S
NDA NDA
Power controller switch
interface driver • USB NDA NDA
1200 MHZ – 144 MHz
down converter NDA - NDA
Power supply 1 • GSS1200
Diamond Antenna
NDA • Microset
13.5 V Power supply 2 • GSV3000
Diamond Antenna
NDA • Microset
13.5 V SWR & power meter 1 • SX-400
(Diamond)
NDA NDA
DSP • Downlink: TNC-
555 (Tasco)
• Uplink: TNC-505 (Tasco)
NDA NDA
Noise filter NDA NDA NDA
Cables • 10D-FB coax
(Fujikura co. ltd.)
• LMR-400 coax
• LMR-600 coax
NDA
PC 1 • DELL NDA • Fujitsu
Siemens
PC 2 NDA NDA • Fujitsu
Siemens
Wide screen NDA NDA NDA
Table 2: Hardware comparison with other Universities
Software
Software University of
Tokyo , Japan
(Ref 15)
California
Polytechnic State University , USA
(Ref 16)
JMUW, Germany (Ref 10)
Operating system Windows XP Linux -
Pre-Pass software • Virtual Ground Station
• MacDopplerPRO X
• SatPC32
• Predict
• Mercury GS system
• Predict Real time software • Virtual
Ground Station
• GMS 6
• GMS Client
• CS
• MacDopplerPRO X
• SatPC32
• Predict
• InstantTrack
• Mercury GS system
• Predict
Past-pass software CS NDA NDA
Software TNC NDA MixW NDA
Table 3: Software comparison with other Universities Remarks:
1. CS - Custom software 2. NDA - No Data Available
Hardware selection
Hardware selection was carried out considering the current and future requirements (communicate via S band) of the IRV ground station, weather conditions in Kiruna, already available equipments and the available budget. Advice and recommendations from collaborative universities/ industries were taken into account during the decision making.
Hardware 1st selection 2nd selection Remarks
Tower CUE DEE - aa
Antenna 1 (2m -VHF) CUE DEE 15 X 144 - aa
Antenna 2 (70 cm -UHF) CUE DEE 17 X 432 - aa
Antenna Rotor YAESU G-5400 B - aa
Rotor controller YAESU G-5400 B - aa
Rotor computer interface GS 232B -
Rotor computer interface driver
RS-232 Winrotor
Radio ICOM IC-910H YAESU FT 736R sa
Preamplifier 1 ( for VHF) ICOM AG-25 ARR P144VDG sa Preamplifier 2 ( for UHF) ICOM AG-35 ARR P435VDG sa
Radio computer interface CT-17 -
Radio computer interface driver
RS-232 CI-V interface -
Power controller switch RBIO-4S -
Power controller switch interface driver
RS-232 - 1200 MHZ – 144 MHz
down converter
UEK-200SAT - aa
Power supply 1 PS 52 SAGA 300 aa
Power supply 2 PS 52 SAGA 300 aa
SWR & Power meter DAIWA CN-460M - aa
Noise Filter DSP-59 + - aa
Cables aircom puls 50 ohm
cables
Nokia communication cables
aa/sa
PC 1 Dell, Intel GHz, 1GB
Ram, 80 GB HDD
-
PC 2 Dell, Intel GHz, 1GB
Ram, 80 GB HDD
-
Wide screen HITACHI 42 Inch -
Table 4: Hardware Selection Remakes:
1. aa- Already available in the ground station 2. sa- Some parts/amount are already available
Software selection
Software selection was carried out considering the current and future requirements (ground station networking) of the IRV ground station, available hardware and the available budget. Advice and recommendations from collaborative universities/ industries were taken into account during the decision making.
Software 1st selection 2nd selection Remarks
Operating system Windows XP Linux -
Pre-Pass software Nova for Windows Virtual Ground Station
Winorbit -
Real time software Nova for Windows Virtual Ground Station GMS
GMS Client AGWTERMINAL CWget
Winorbit Winorbit
Hamscope
-
Past-pass software AGWTERMINAL
CWget Hamscope
-
Software TNC Packet Engine Pro - -
Table 5: Software selection
Cost of finance
Item Cost (SEK)
Tower 15000*
Antenna 1 (2m -VHF) 1272
Antenna 2 (70 cm -UHF) 1080
Antenna Rotor 5000*
Rotor controller -
Rotor computer interface 5200
Rotor computer interface driver -
Radio 18000
Preamplifier 1 ( for VHF) 1500
Preamplifier 2 ( for UHF) 1540
Radio computer interface 840
Radio computer interface driver -
Power controller switch 2000
Power controller switch interface driver - 1200 MHZ – 144 MHz down converter -
Power supply 1 2000*
Power supply 2 2000*
SWR & Power meter 1 1750
Noise filter -
Cables 10000*
PC 1 10000
PC 2 10000
Wide screen 18000
GMS -
GMS Client -
Packet Engine pro 500
Nova for windows 500
Hamscope - CWget -
AGWTERMINAL -
TOTAL 106182
Table 6: Cost of finance as at 2006 Remarks:
1. Most of the prices are taken from the invoices and some are from the internet 2. *: Approximate value
Antenna theory
Antennas are the most important part of a ground station. They are the essential link between free space and the transmitter or receiver and play a vital part in determining the characteristics of the complete system. Design of antennas and its working environment will decide the effectiveness of any given ground station (Ref 16). In this section attention is given only to the UHF and VHF antennas.
Polarization
Figure 05: E-field variation of Linear and Circular polarization.
The polarization of the signal is identified from the direction of the e-field vector. Mainly there are two kind of polarization.
• Linear polarization
• Circular polarization
If the e-field vector exists in vertical plane then the polarization is liner and vertical. If the e-field vector exists in horizontal plane then the polarization is liner and horizontal.
Simple way to identify which polarization an antenna communicate when it transmit (or is most sensitive for which polarization during receiving) is to note the direction of the radiator elements (figure 05). For vertical polarization the radiator elements are vertical and for horizontal polarization the radiator elements are horizontal. (Ref 1, Ref 3, Ref 20)
Radiator elements
Ref 20
If the signal is composed of two plane waves of equal amplitude but differing in phase by 90°, then the signal is said to be circularly polarized. The tip of the electric field vector appears to be moving in a circle. If the electric vector of the electromagnetic wave appears to be rotating clockwise (as it coming toward), the wave is said to be right- circularly polarized. If it rotates counter clockwise, then it is said to be left-circularly polarized. (Ref 3, Ref 2)
Standing Wave Ratio (SWR)
SWR is a measurement of how efficiently the antenna system will radiate the power available from the radio. In simple terms, the radio would like to radiate all of its power, but can only do so if the other components cooperate. Bad coaxial cables and mounts, or inefficient antennas and ground plane can cause system bottlenecks.
There are several methods to measure SWR.(Ref 1) Measuring the maximum and minimum voltage along the line and using equation 1 can calculate the “Voltage Standing Wave Ratio” (VSWR).
Or it is possible to calculate by comparing the antenna feedpoint resistive impedance (ZL) to the transmission line characteristic impedance (Z0). Equation 2 or 3 can be use for impedance comparing.
It is possible to measure the forward power (PF) and reflected power (PR) to calculate the SWR (by using equation 4).
VSWR = VMAX
VMIN (1)
(ZL > Z0 )
VSWR = ZL
Z0
(3) (Z0 > ZL )
VSWR = Z0
ZL
(2)
+ SWR = √PF - √PR
√PR
√PF
(4)
Antenna bandwidth
Bandwidth of an antenna refers generally to the range of frequencies over which the antenna can be used to obtain a specified level of performance. The bandwidth is often referenced to some SWR value. But SWR bandwidth is not always related to gain bandwidth. (Ref 1)
Impedance
The impedance at a given point of the antenna is determined by the ratio of the voltage to the current at that point. Antenna impedance may be either resistive or complex depending on whether the antenna is at resonant at the operating frequency. (Ref 1)
Directivity of the antenna and antenna beamwidth
All antennas are exhibit directive effects, means, some directions will have more radiation compare to other directions. This property is called as the directivity of the antenna. A directional antenna radiates and receives through a main lobe and several side lobes (as shown in figure 06). The side lobes are usually undesirable, as they attract spurious noise, and efforts are made through the antenna design to suppress them. As shown in the figure 06 the antenna beam width is the 3 dB angle respect to its bore site maximum power. (Ref 3)
Figure 06: Definition of antenna beamwidth Ref 03
Radiation Pattern
A graphical representation of the intensity of the radiation of the antenna plotted against the angle (from the perpendicular axis). The graph is usually circular, the intensity indicated by the distance from the centre. (Ref 8, Ref 9)
Gain of the antenna
The gain of an antenna is a combination of directivity and efficiency when compared with a reference antenna. Normally the reference antenna will be an isotropic one.
Omnidirectional antennas
Omnidirectional antennas are the simplest one that can use in a ground station. It will simplify the building of the ground station tremendously, as no rotors or rotor interface are needed. Most of the amateur satellites can be heard by using omnidirectional antennas. The “Discone” antenna (figure 06) is often used where a single omnidirectional antenna covering several VHF/UHF bands is required. The Discone antenna consist of a disc mounted above a cone, and ideally should be constructed from sheet material. There will be a small loss of performance if the components are made of rods or tubes. At least 8 or preferably 16 rods are required for the disk and cone for reasonable results. This kind of antenna is capable of covering the 70,144 and 432 MHz bands or 144, 432, 1290 MHz.
(Ref 8)
Figure 06: Omnidirectional antenna (Discone type) Disk
Cone
Rods
Ref 08
Antenna can be operate over roughly a 10:1 frequency range. Since the antenna is radiate harmonics present in the transmitter output, it is needed to use suitable filters for attenuation. These antennas have VSWR of less than 2:1 over the octave range. Figure 07 and 08 shows the radiation patterns of a Discone antenna for 145 MHz and 435 MHz bands. (Ref 1, Ref 3, Ref 7, Ref 9, Ref 10)
Figure 07: Discone antenna elevation radiation patterns for 145 MHz
Figure 08: Discone antenna elevation radiation patterns for 145 MHz Ref 08
Ref 08
Yagi antennas
Since most of the student satellites produce low strength (due to the low power) circular polarized waves (due to the spinning of the satellites) it is preferred to use Yagi antennas.
The number of elements on a Yagi and array length is directly proportional to the gain of the antenna. More elements mean more gain but smaller beamwidth. The array length is of greater importance than the number of elements, within the limit of a maximum element spacing of just over 0.4λ.
The antenna should mount considering the polarization of the wave. The difference between horizontal and vertical polarization is (theoretically) infinite. If the orbiting antenna is horizontally polarized and ground station antenna is vertically polarized, nothing will receive. If the orbiting antenna circularly polarized and ground satiation antenna linearly polarized then maximum loss will be 3 dB. But if the orbiting and ground satiation antennas are circularly polarized then maximum loss can be 10 dB due to the polarization mismatch. (Ref 1, Ref 3, Ref 7, Ref 9, Ref 10)
Figure 09: Skeleton slot fed Yagi antenna
The simplest way of being able to select polarisation is to mount a horizontal Yagi and a vertical Yagi on the same boom giving the cross Yagi antenna configuration (shown in
Ref 08
figure 10). Separate feeds to each section of the Yagi brought down to the operation position enable the user to switch to either horizontal or vertical polarization.
Figure 11 shows the voltage polar diagram and gain against VSWR of Yagi antennas for six and eight elements. (Ref 8)
Figure 10: Cross Yagi antenna
Figure 11: Voltage polar diagram and gain against VSWR for Yagi antennas Ref 08
Ref 08
Digital communication
In the context of TT&C digital communication is much more interest than the analog communication. Specially most of the student satellites are communicating via JD satellite mode.
In digital communication the Bit Error Ratio (BER) is the primary quality criterion. BER must be keet at minimum to obtain a better link quality. Normally suitable modulation methods and forward error correction (FEC) methods are using to minimize the BER.
FEC will give a considerable coding gain and therefore FEC acts like a virtual amplifier(Ref 3).
Where
C: Carrier power N: Noise power
(C/N): Carrier to noise ratio
(5)
(6)
(7)
(8)
N0 = N/B (9)
Eb: Amount of energy manage to pack in to the each bit in a digital data stream (C/r) r: Bit rate ( bits per second)
N0: Normalize noise power with respect to the bandwidth (Noise spectral density) B: Frequency Bandwidth
(C/N)req : Required carrier to noise ratio (C/N)ach : Achieved carrier to noise ratio
Link Budget
A link budget is the accounting of all of the gains and losses from the transmitter to the receiver in a satellite communication system. When calculating the link budget, it is in practice to calculate both preliminary and detail link budgets. Normally preliminary link budget is calculated to find out the rough value of the link margin. When calculating the preliminary link budget the losses are not taking in to account. For the telemetry the system noise temperature (Tsys) is decided by considering only the galactic and tropospheric noise temperatures (commonly is taken as 80 K) and it is used to determine the carrier-to-noise ratio. In the detail link budget, the noise and attenuation due to various sources are taken in to account (Ref 3).
To achieve an acceptable quality signal, following requirement must be fulfilled.
Link margin
Is the difference between ‘Achieve (C/N) and required (C/N) in dB for a particular BER
The Minimum required link margin for a good reception is approximately 3 dB in a detail link budget and 10 dB for the preliminary link budget (in case of unexpected link losses)
(Ref 3)
(10)
Link margin = (C/N)ach (dB) – (C/N)req (dB) (11)
Calculation of (C/N)ach
In a satellite communication system the received power can be expressed as following relationship
Where
Pt: is transmitted power in Watts Pr: is received power in Watts Gt: is transmitter antenna gain Gr: is receiver antenna gain λ: is the wave length
d: is the distance between satellite and the ground station
To distinguish the received signal from the noise it is important to know the relationship between carrier power (C), induce noise power (N); and from that it is possible to calculate the carrier-to-noise ratio (C/N) (Equation 12).
Where
k: Boltzman constant ( 1.38 x 10-23 J/K) T: Noise temperature
c: Speed of light ( 3.108 m/s) f: Frequency
2
4 ⎟
⎠
⎜ ⎞
⎝
= ⎛
G d G P P
r t t rπ
λ
(12)[Watts]
(13)
(14) (15)
EIRP: Equivalent Isotropic Radiated Power (transmit power (Pt) multiply by the transmit antenna gain (Gt))
Equation needed to calculate the (C/N)req for detail link budget
Where
And L1, L2 are the losses causes due to the weather, antenna pointing errors, polarization mismatch etc.
Figure 12: Worst case distance between the satellite and the ground station
Here “d” is the worst case distance when the elevation angle δ.
For the non-zero elevation angle, the distance is “d’”
(16)
(17) Ref 03
Receiver figure of merit
Gr/T: the amount of thermal noise picked up by the antenna side lobes
Losses
Free space loss
The quantity of {λ/ (4πd)} 2 is know as the free space loss (from equation 12); the amount of the radio signal dissipated in free space.
Losses due to the O2 and Water vapour
Figure 13: Clear sky radio signal attenuation due to oxygen and water vapour in the atmosphere
Note : Thickness of the O2 layer ~ 5 Km, thickness of the H2O layer ~2 km. O2
attenuation loss Latm can be obtain by using the figure 13 and calculating the path length of the signal through the O2 layer (by using equation 18, here h=5 km).
(18)
Ref 03
System noise temperature
During the telecommand the satellite antenna is looking down at earth. Therefore it sees the earth surface and some surrounding space. During the telemetry the ground station antenna looks up and sees sun, moon, outer space, the ionosphere, the troposphere, surrounding topography etc.
Where
Tsys: System noise temperature
Tant: Noise temperature collected by the satellite antenna due to the earth radiation during the telecommand and noise temperature collected by the ground station antenna due to various sources (sun, moon etc) during telemetry.
Lline: Resistive noise contribution from the signal line (between antenna and receiver) Trx: Noise temperature depending on chosen frequency and receiver technology
Figure 14: Galactic and tropospheric noise temperatures at various ground antenna elevations (δ)
(19)
Ref 03
Figure 14 shows galactic and tropospheric noise temperatures at various ground antenna elevations δ. Here it assumes that, the ground station antenna never sees sun or moon during the telemetry.
Noise temperatures due to hot bodies
If the ground station antenna sees the sun or moon during the telemetry then the noise temperatures should take in to account (equation 20). The sun is treated as a hot body with a temperature of 5805 K and moon is treated as a hot body of temperature of 200K.
Where α is the fraction that heat source occupies within the antenna coverage (3 dB beam width)
Ground station receiver noise
Ground station receivers produce noise depending on their technology. Figure 15 shows the relationship between ground station technology, noise temperature and frequency.
Figure 15: Ground station receiver noise
(20)
Ref 03
Noise and attenuation due to Rain
Rain fall introduces attenuation by absorption and scattering of signal energy, and the absorptive attenuation introduces noise.
Figure 16 shows the attenuation loss due to rain (Lrain) and the corresponding noise temperature (Train) where rain rate measured in mm/h and it is assumed that the cloud temperature is 290K and the antenna boresight elevation angle is 30 deg above the local horizon.
Figure 16: Attenuation Lrain and noise temperature due to rainfall at 30 deg elevation above the local horizon
The thickness of the rainy part of the atmosphere is 3 km at elevation angle 90 deg. The equation 22 gives the elevation dependent thickness.
(21)
(22) Ref 03
Equation 23 gives the induce loss due to rain according to the elevation angle.
Line noise and attenuation
A typical coaxial cable causes a signal loss of 0.5 dB per meter. Therefore a 1 meter cable represents a loss [Lline] =0.5 dB, corresponding to Lline=1.1. This loss also gives rise to an equivalent noise temperature. Equation 24 shows the relationship between line losses to the noise temperature.
Polarization loss
The maximum polarization isolation between an antenna with linear polarization and one with circular polarization is 3 dB. Equation 25 gives the relationship between the polarization loss and the mismatch angle. The equation 26 shows the relationship between the signal frequency and the average day time Faraday rotation angle (Ref 3).
Where Ф is the mismatch angel and/or average day time Faraday rotation angle
Antenna pointing loss
(23)
(24)
(25)
(26)
(27)
Where
θ3dB : is the antenna beamwidth in degrees ε : is the pointing error in degrees
Implementation losses
0.5 to 3 dB due to the frequency dependent losses in the hardware Summary of sources of Noise and Losses
Here Ts is the sum of all noise temperature contributions. Lline1, Lline2 and Lpoint1 and Lpoint2 represent the line and pointing losses in both transmitter and receiver sides.
Global Educational Network for Satellite Operation (GENSO)
GENSO is a project that initiated under the auspices of the International Space Education Board (ISEB). This board consists of the Education Departments of the Canadian Space Agency (CSA), the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA) and the National Aeronautics and Space Administration (NASA).
Currently the project is managed by the Education Projects Division of ESA. It is expect to run a first pilot phase of the project in the summer of 2007. The main objectives of this GENSO project are (Ref 18)
• To provide unparalleled near-global levels of access to educational spacecraft in orbit,
• To allow remote access for operators to real-time mission data, even in cases when their local ground station is experiencing technical difficulties,
• To provide remote control of all participating ground stations,
• To optimise uplink fidelity by calculation of real-time link budgets and uplink station selection,
• To perform downlink error-correction by comparing multiple data streams,
(28)
• To define and implement a global standard for educational ground segment software,
• To define and instantiate an optional well-defined standard solution for educational ground-segment hardware (in order to expedite participation in GENSO),
• To support a common interface for applying for frequency allocation and coordination.
CHAPTER 3
IRV GROUND STATION STATUS
Ground station specification
Ground station name SK2UL
University Luleå University of Technology
City Kiruna
Country Sweden
Altitude 382 m
Latitude 67.7 N
Longitude 20.3 E
Tower CUE DEE
Operating frequencies 144-146 MHz, 432-438 MHz
Antenna 1 (2m –VHF) (Gain: 13 dB)
(Beamwidth: 44 deg)
CUE DEE 15 X 144
Antenna 2 (70 cm –UHF) (Gain: 14 dB )
(Beamwidth: 40 deg )
CUE DEE 17 X 432
Antenna Rotor Yaesu G-5400B
Rotor controller Yaesu G-5400B
Rotor computer interface Yaesu GS 232B
Rotor computer interface driver RS 232
Radio 1 ICOM 910H
Radio 2 YAESU FT-736 R
Preamplifier 1 ( for VHF) (Gain: 15 dB )
ICOM AG-25 Preamplifier 2 ( for VHF)
(Gain: 24 dB)
ARR P144VDG Preamplifier 3 ( for UHF)
(Gain: 15 dB)
ICOM AG-35 Preamplifier 4 ( for UHF)
(Gain: 24 dB) ARR P435VDG
Radio computer interface CT-17
Radio computer interface driver RS-232 CI-V interface
Power controller switch RBIO-4S
Power controller switch interface driver RS 232
1200 MHZ – 144 MHz down converter UEK-200SAT
Power supply 1 Kenwood PS-52
Power supply 2 SAGA 300
SWR & power meter 1 DAIWA CN-101L
SWR & power meter 2 DAIWA CN-460M
Noise filter DSP-59 +
Cables ECOFLEX-10 LAGFORLUST Nokia telecommunication cables aircom puls 50 ohm cables
PC 1 Dell, Intel 3 GHz, 1GB Ram, 80 GB
HDD
PC 2 Dell , Intel 3 GHz, 1GB Ram, 80 GB
HDD
Wide screen HITACHI 42 Inch
Operating system Windows XP
Pre-pass software Nova for Windows
Winorbit
Virtual Ground Station
Real time software Nova for Windows
Winorbit
Virtual Ground Station GMS
GMS Client AGWTERMINAL Hamscope
CWget
Past-pass software AGWTERMINAL
Hamscope CWget
TNC software Packet Engine pro
Table 7: IRV ground station specifications
Description of used hardware and software Tower and antennas
Figure 17: UHF/VHF Yagi antennas
Antennas are the transducers that convert the wave signal into an electrical signal and vice versa. The present configuration uses two antennas mounted on a 4 m high aluminium tower. These are:
CUE DEE 15X 144 Antenna used for a frequency range of 144 to 146 MHz CUE DEE 17 X 432 Antenna used for a frequency range of 432 to 438 MHz
Transceivers
ICOM IC-910H (All Modes) transceiver is used. The IC-910H is a 144 MHz /440 MHz/1.2 GHz all mode satellite radio. It features a powerful 100 W of output on 2 meter band, and 75 W on 70 cm band.The IC-910H has two data sockets for simultaneous two band packet communications. High speed PLL lockup time makes 9600 bps high speed packet communications possible.
Figure 18: Picture of the ICOM IC-910H transceiver
Rotor and rotor controller
The Yaesu G-5400B provide 360 deg azimuth and 180 deg elevation control of medium and large-size unidirectional satellite antenna arrays under remote control from the station operating position. The two factory-lubricated rotator units are housed in weather- proof melamine resin coated die-cast aluminium. Rotor contains a thermal sensor to prevent damage from overheating during periods of high usage.
The controller unit is a desktop unit with dual meters and direction controls for azimuth and elevation.
Figure 19: Rotor and Rotor controller
Preamplifiers
Both “ICOM AG” and ARR GaAsFET type of preamplifiers are used in the ground station. The “ICOM AG” type preamplifiers are water proof all weather type with improved S/N ratio and receiver sensitivity, and make DX-communication possible. The coaxial cable is working also as the DC cable.
Figure 20: AG-25/AG-35 preamplifier
ARR GaAsFET preamplifiers have been specifically designed for amateur use. Each unit is housed in a completely shielded, rugged, custom aluminium enclosure. To maintain a high degree of RF shielding a feed-through type capacitor is provided for the DC ground connection. These preamplifiers are suitable for fixed, mobile, or portable operations.
Power supply requirements are 10-16 Volts DC supply with 15 mA current.
Figure 21: ARR GaAsFET Preamplifier
Radio Computer Interface
ICOM CT-17 is using to connect the transceiver to the PC via the PC's RS-232C port.
This allows to control the Radio from the PC and/or transfer the data from the receiver to the PC. Control is provided via ICOM's CI-V communication interface.
Figure 22: ICOM CT-17 Radio Computer Interface
Rotor Computer Interface
The GS-232B provides digital control of Yaesu antenna rotators from the serial port of an external personal computer. The async serial line can be configured for serial data rates from 1200 to 9600 baud. Firmware of the GS-232B supports either direct key board control, or commands from programs written specially to support it.
Figure 23: GS-232B Rotor Computer Interface
Power controller switch
Figure 24: Power controller switch
RBIO-4S power switch is used to switch on/off all the hardware via computer command.
Computer serial interface is used to connect to the PC and “OMRON” 10 A, 264 VAC solid state relays are using as the switches.
The UEK-200SAT receive converter
The UEK-200SAT is an S-band receive converter. UEK-200SAT provides approximately 50 MHz of RF bandwidth starting at 2400 MHz as well as 50 MHz bandwidth starting at 144 MHz. The UEK-200SAT is constructed on Teflon printed circuit board material to achieve low losses and excellent noise figure at 2400 MHz.
Figure 25: UEK-200SAT receive converter
Power supply
“Kenwood PS-52” and “Saga 300” power supplies are used to power the hardware.
Kenwood PS-52 (13V, 20 Amp) is used to power the transceiver, the CT-17 communication interface and the GS-232B Rotor computer interface. Saga 300 (13.8 V, 3 Amp) is used to power the ARR GaAsFET preamplifiers (when they used instead of ICOM AG preamplifiers).
Figure 26: Kenwood PS-52 Power supply
Figure 27: SAGA 300 Power supply
SWR & Power meter
Figure 28: SWR & Power meter (1.8 – 150 MHz)
SWR and power indicators are installed in single meter unit. One scale will indicate forward power; another scale reflected power and SWR is indicated at the crossing point of the 2 needles. This unique feature makes it possible to read forward power, reflected power, and SWR all at the same time.
Figure 29: SWR & Power meter (140 -450 MHz)
Audio Noise Reduction filter
The DSP-59 + is an audio noise filter for amateur radio voice, data and CW operation.
This filters and reduces noise and interference to improve the radio reception. The DSP- 59+ uses digital signal processing technology to implement algorithms that perform three basic filter functions
1. Random noise reduction
2. Adaptive multi-tone notch filtering ( Tone noise reduction) 3. Band-pass / High-pass / Low-pass filtering
Push-button switches permit simultaneous selection of these three functions
Figure 30: Audio Noise Reduction filter
Cables
“ECOFLEX-10 LAGFORLUST” Co-axial cables, “Nokia” telecommunication cables and “aircom puls” 50 ohm coaxial cables are used (details in appendix 1). The length of the cable is about 25 m from the antenna to the transceiver.
Connection of hardware
Figure 31: Hardware connection Rotor
Computer
IC 910H CT-17
PS-52
GS-232B
G-5400B AG-35
UHF Antenna VHF Antenna
AG-25
Software setup Pre-pass software
Nova for windows software, win orbit software, and “Virtual Ground Station” software (developed by the Tokyo University) are using as pre-pass software to determine the Satellite AOS, LOS, azimuth and elevation angels.
Real time software
Nova for windows software, win orbit software, and “Virtual Ground Station” software are used to determine the Satellite crossing times, elevations and azimuth angles according to the satellite position.
GMS (Ground Station Management Service) (Ref 12) software (developed by the Tokyo University) is used to control the radio and the antennas autonomously according to the satellite position.
The “Packet Engine Pro” a software based TNC (Terminal Node Controller) and a terminal program (AGWTERMINAL) are used to decode and encode the AX.25 packets in real time. The “Hamscope” software and “CWget” software are used to decode the CW beacons in real time.
Past-pass software
The “Packet Engine Pro” a software based TNC (Terminal Node Controller) and a terminal program (AGWTERMINAL) are used to decode the AX.25 packets from a recorded satellite downlink. The “Hamscope” software and “CWget” software are used to decode the CW beacon from a recorded downlink CW signal.
Operational Procedure
This section gives a brief detail of how the entire system works and can be controlled.
1. Identify the target satellite.
After knowing the satellite, its beacon, uplink and downlink frequencies can be obtained from the satellite webpage or satellite detail sheet.
2. To obtain the updated TLE (Two Line Elements)
The updated TLE of the satellite can be obtained from internet (Ref 17)
3. To determine the AOS, LOS, azimuth and elevation angles.
The updated TLE is used in the Nova for windows software, “Virtual Ground Station” software or “Winorbit” software to determine the AOS, LOS, azimuth and elevation angles.
4. Controlling the antenna rotor and the transceiver
For this the “GMS” software is used. The satellite details and the ground station details are fed in to the GMS client program. First the frequency of the transceiver is fixed to the beacon frequency to detect the satellite when it’s in range. Then the transceiver is fixed to the telemetry and telecommand frequencies to communicate via AX.25 packets.
5. To start the communication via AX.25 packets, the software TNC program and the terminal (AGWTERMINAL) program are used.
6. To start the communication via CW, the “Hamsocpe” program or “CWget”
program is used.
CHAPTER 4
IRV GROUND STATION PERFORMANCE ANALYSIS
During the IRV ground station performance analyses following tasks were carried out.
1. Calculating the preliminary downlink budget for 70 cm antenna system 2. Calculating the preliminary uplink budget for the 70 cm antenna system 3. Calculating the preliminary downlink budget for 2 m antenna system 4. Calculating the preliminary uplink budget for the 2 m antenna system 5. Experiments to find out the data decoding ratio of the ground station
6. Experiments to find out the overall data downloading ratio compare to other ground stations
7. Experiments to find out the required minimum elevation angle (δ) 8. SWR measurements in 70 m antenna system
9. SWR measurements in 2 m antenna system
10. Monitoring the external electromagnetic interferences in amateur radio bands Preliminary link budget
The preliminary link budget is calculated to get a rough idea about the required minimum EIRP for a successful downlink and/or uplink. Since the ground station EIRP is directly known from its antenna gain and transmitter power, it is possible to calculate the required minimum antenna gain for the spacecraft. Or for a known spacecraft it is possible to calculate the required minimum EIRP from the ground station and check whether the ground station EIRP is sufficient for successful uplink. For the calculation the earth radius has taken as 6371 km and the Noise temperature (T) assumed as 80 K. Here it is assumed that the required link margin is 10 dB and required minimum ground station elevation angle (δ) is 10 degrees for a successful communication. The bit error rate for AFSK modulation is assumed as 10-5.
No Parameter Liner value
dB Remarks 1 Max satellite altitude h ( km) 850.00
2 Radial distance (km) 7221.00
3 Bit rate (bps) 1200.00
4 Bit error rate 1.00E-05 Assumed
5 Modulation method AFSK
6 Min elevation angle (deg) 10.00
7 Link frequency (MHz) 450.00
8 Ground station antenna gain (dB) 14.00 9 Ground station antenna beamwidth
(deg)
40.00 70 cm
antenna
9 Noise temperature T ( K) 80.00
10 Boltzmann constant μ (J/K) 1.38E-23
(C/N) req
11 Bandwidth B ( Hz) 2.70E+03 Ref 19
12 Eb/N 4.01E-03 Eq 6
13 Eb/N0 1.08E+01 Eq 8
14 C/N req 4.81E+00 6.82 Eq 7
(C/N) ach
15 Max distance d (km) 2.47E+03 Eq 18
16 Wave length (m) 6.67E-01 Eq 15
17 Max free space loss 4.62E-16 -153.35 Eq 12
18 Required link margin (dB) 10.00 Assume
19 (C/N) ach ( Required) 16.82 Eq 11
20 GS Noise Power N 2.98E-18 -175.26 Eq 14
21 GS received power (Required) -158.44 19+20 22
Minimum EIRP
( Required from SC) -19.09 Eq 12
Table 8: Preliminary downlink budget for 70 cm antenna
No Parameter Liner value
dB Remarks 1 Max satellite altitude h ( km) 8.50E+02
2 Radial distance (km) 7.22E+03
3 Bit rate (bps) 1.20E+03
4 Bit error rate 1.00E-05 Assumed
5 Modulation method AFSK
6 Min elevation angle (deg) 1.00E+01
7 Link frequency (MHz) 1.44E+02
8 Ground station antenna gain (dB) 13.00 9 Ground station antenna beamwidth
(deg)
4.00E+01 70 cm
antenna
9 Noise temperature T ( K) 8.00E+01
10 Boltzmann constant μ (J/K) 1.38E-23
(C/N) req
11 Bandwidth B ( Hz) 2.70E+03 Ref 19
12 Eb/N 4.01E-03 Eq 6
13 Eb/N0 1.08E+01 Eq 8
14 C/N req 4.81E+00 6.82 Eq 7
(C/N) ach
15 Max distance d (km) 2.47E+03 Eq 18
16 Wave length (m) 2.08E+00 Eq 15
17 Max free space loss 4.51E-15 -143.45 Eq 12
18 Required link margin (dB) 10.00 Assumed
19 (C/N) ach ( Required) 16.82 Eq 11
20 GS Noise Power N 2.98E-18 -175.26 Eq 14
21 GS received power (Required) -158.44 19+20 22
Minimum EIRP
( Required from SC) -27.98 Eq 12
Table 9: Preliminary downlink budget for 2 m antenna
No Parameter Liner value
dB Remarks 1 Max satellite altitude h ( km) 850.00
2 Radial distance (km) 7221.00
3 Bit rate (bps) 1200.00
4 Bit error rate 1.00E-05 Assumed
5 Modulation method AFSK
6 Min elevation angle (deg) 10.00
7 Link frequency (MHz) 450.00
8 Ground station antenna gain (dB) 14.00 Ground Station Transmitter Power
(W) 75
18.75 9 Ground station antenna beamwidth
(deg) 44.00 70 cm
antenna 9 Noise temperature at receiver T ( K) 80.00
10 Boltzmann constant μ (J/K) 1.38E-23
(C/N) req
11 Bandwidth B ( Hz) 2700.00 Ref 19
12 Eb/N 4.01E-03 Eq 6
13 Eb/N0 1.08E+01 Eq 8
14 (C/N) req 4.81E+00 6.82 Eq 7
(C/N) ach
15 Max distance d (km) 2.47E+03 Eq 18
16 Wave length (m) 6.67E-01 Eq 15
17 Max free space loss 4.62E-16 -153.35 Eq 12
18 Required link margin (dB) 10.00 Assume
19 (C/N) ach 16.82 Eq 11
20 SC Noise Power N 2.98E-18 -175.26 Eq 14
21 GS EIRP 262.51 19+20
22
Minimum required SC antenna
gain -267.59 Eq 12
Table 10: Preliminary uplink budget for 70 cm antenna
No Parameter Liner value
dB Remarks 1 Max satellite altitude h ( km) 850.00
2 Radial distance (km) 7221.00
3 Bit rate (bps) 1200.00
4 Bit error rate 1.00E-05 Assumed
5 Modulation method AFSK
6 Min elevation angle (deg) 10.00
7 Link frequency (MHz) 144.00
8 Ground station antenna gain (dB) 13.00 Ground Station Transmitter Power
(W)
100
20.00 9 Ground station antenna beamwidth
(deg)
44.00 2 m antenna 9 Noise temperature at receiver T ( K) 80.00
10 Boltzmann constant μ (J/K) 1.38E-23
(C/N) req
11 Bandwidth B ( Hz) 2700.00 Ref 19
12 Eb/N 4.01E-03 Eq 6
13 Eb/N0 1.08E+01 Eq 8
14 (C/N) req 4.81E+00 6.82 Eq 7
(C/N) ach
15 Max distance d (km) 2.47E+03 Eq 18
16 Wave length (m) 2.08E+00 Eq 15
17 Max free space loss 4.51E-15 -143.45 Eq 12
18 Required link margin (dB) 10.00 Assumed
19 (C/N) ach 16.82 Eq 11
20 SC Noise Power N 2.98E-18 -175.26 Eq 14
21 GS EIRP 260.00 19+20
22
Minimum required SC antenna
gain -274.98 Eq 12
Table 11: Preliminary uplink budget for 2 m antenna
CUTE-1 FM operation to find out the decoding ratio of IRV ground station
The experiments were conducted during the handover pass with Tokyo (UT) - Kiruna (IRV). First, during the link time in Tokyo, UT ground station sent the command to the CUTE-I to start the FM downlink. During the handover from Tokyo to Kiruna, both ground stations successfully received the FM telemetry (FM packets from CUTE-I) data at each link time. As a result of this collaborative operation continuous status data was obtained for more than 15 minutes. The interval time (time between LOS at Tokyo (UT) and AOS at Kiruna (IRV)) between the each link time was only 3 minutes (theoretically) but the interval time obtained from the experiment was about 8 minutes (as shown in figure 32). This is because of its difficulty in data decoding in low elevation angle.
Figure 32: Plot of time stamps of decoded packet at each ground station
Note:
1-Orange dots: Tokyo (UT) 2-Blue dots: Kiruna (IRV)
Packet decoding rate for CUTE-1 cube satellite
The interval time for packet output for CUTE-1 was 4 seconds 76(packets) / 158 (packets) = 48.25%
1 2
XI-IV FM operation to find overall data download ratio Handover experiments were carried out for the passes
1. Tokyo (UT) –Kiruna (IRV)
2. Kiruna (IRV) – California Polytechnic State University (CalPoly)
During the link time the respective ground stations uplink the commands to achieve the downlink data and more than 60 Kbytes of data (68% of the total picture data stored in the CUTE-1) were downloaded using 3 ground stations. The status data (three times for each pass) and all the picture data from ROM 2, 3, 4 and 5 (data from ROM 1 was not able to download during the experiment) were downloaded. Figure 33 shows the amount of data obtained during the experiment. During the handover passes of Tokyo (UT) – Kiruna (IRV) all the offset data sets were completely downloaded from ROM 2 and ROM 5 and the handover passes of Kiruna (IRV) - CalPoly the data sets of ROM 4 were completely downloaded.
Figure 33: Comparison of downloaded data at each pass.
Local Time (@Kiruna) [hour]
Figure 34: The integration of obtained data at each operation time.
Figure 35: The ratio of obtained data at each ground station
Figure 33 shows the comparison of the download data by each ground station. Figure 34 shows the cumulative value of downloaded data from each ground station. And figure 35 shows the total percentage of data downloaded by each ground station.
Local Time (@ Kiruna) [hour]
Packet decoding rate for XI-IV cube satellite 438(packets) / 1364(packets) = 32.1%
(In case of uplink success rate to be 90%, 438 / (1364 X 0.9) = 35.7%) Interference monitoring
Frequency scanning in VHF and UHF amateur radio bands were carried out once in every hour for few days to track or listen to any kind of electromagnetic interference or radio traffic.
Only the thermal noise can be hear when receivers are used at high sensitivity mode. But it was not able to hear any kind of electromagnetic interference or radio traffic in normal conditions.
Testing of the SWR for the antenna systems
SWR was measured by using SWR meters and the reading was below 2 for both VHF and UHF antenna systems
