Principles of Satellite Communications, 4-2 - Lab-Volt

Principles of Satellite Communications, 4-2 - Lab-Volt
Exercise
4-2
Troubleshooting the Earth Station Receiver
EXERCISE OBJECTIVE
When you have completed this exercise, you will have used a systematic
technique of signal flow tracing to diagnose instructor-inserted faults in the Earth
Station Receiver.
DISCUSSION
Troubleshooting the Earth Station Receiver
Troubleshooting the Earth Station Receiver involves observing the RF, IF, and
baseband signals under various conditions. Use the oscilloscope to observe
signals at the different test points and at the BNC connectors. Use the spectrum
analyzer to observe the IF and RF signals. A voltmeter / power meter may also
be useful.
During the course of this exercise, the instructor will insert faults in the Earth
Station Receiver only. It is important, however, to observe all signals in the
system as you troubleshoot the receiver. It can be particularly useful to compare
the baseband signals in the receiver and in the transmitter, at different stages of
baseband processing.
a
PROCEDURE OUTLINE
The Procedure is divided into the following sections:
ƒ
ƒ
ƒ
PROCEDURE
There are no faults in the Analog Demodulator section of the Earth Station
Receiver. Analog communication may be useful, however, in locating faults in
other sections of the module.
System startup
Observing normal operation
Troubleshooting an unknown fault
System startup
1. If not already done, set up the system and align the antennas visually as
shown in Appendix B.
2. Make sure that no hardware faults have been activated in the Earth Station
Transmitter or the Earth Station Receiver.
b
Faults in these modules are activated for troubleshooting exercises using DIP
switches located behind a removable panel on the back of these modules. For
normal operation, all fault DIP switches should be in the “O” position.
3. Turn on each module that has a front panel Power switch (push the switch
into the I position). After a few seconds, the Power LED should light.
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Ex. 4-2 – Troubleshooting the Earth Station Receiver  Procedure
4. If you are using the optional Telemetry and Instrumentation Add-On:
x
Make sure there is a USB connection between the Data
Generation/Acquisition Interface, the Virtual Instrument, and the host
computer, as described in Appendix B.
x
Turn on the Virtual Instrument using the rear panel power switch.
b
x
If the TiePieSCOPE drivers need to be installed, this will be done
automatically in Windows 7 and 8. In Windows XP, the Found New
Hardware Wizard will appear (it may appear twice). In this case, do not
connect to Windows Update (select No, not this time and click Next). Then
select Install the software automatically and click Next.
Start the Telemetry and Instrumentation application. In the Application
Selector, do not select Work in stand-alone mode.
b
If the Telemetry and Instrumentation application is already running, exit
and restart it. This will ensure that no faults are active in the Satellite
Repeater.
Observing normal operation
5. Make the connections shown in Figure 4-3.
Binary Sequence
Generator
(BSG) 1
Binary Sequence
Generator
(BSG) 2
Binary Sequence
Generator
(BSG) 3
BIT
CLOCK
DATA
DATA
INPUT 1
RF
OUTPUT
DATA
IF 1
OUTPUT
DATA
INPUT 2
Digital
Modulator
DATA
DATA
INPUT 3
Up Converter
1
Up Converter
2
Earth Station Transmitter
BIT CLOCK OUTPUT
I Q
I Q
Satellite
Repeater
RF OUTPUT
Earth Station Receiver
Down Converter
2
Down Converter
1
Digital
Demodulator
I Q
I Q
IF 2
OUTPUT
Figure 4-3. Connections for transmission and reception of TDM data.
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Ex. 4-2 – Troubleshooting the Earth Station Receiver  Conclusion
6. Using the appropriate instruments, review the normal operation and signals
in the Earth Station Receiver. Print or sketch the instrument screens that you
think will be useful for reference.
Compare the signals in the receiver with the corresponding signals in the
Earth Station Transmitter.
Consult your answers to procedure step questions and notes taken while
using the Earth Station Receiver.
7. Make sure that all instruments used for troubleshooting purposes are
operating normally.
Troubleshooting an unknown fault
8. Ask your instructor to activate a fault in the Earth Station Receiver.
9. Carry out the troubleshooting procedure in order to locate the fault and
diagnose the problem. Write your results on a Troubleshooting Worksheet
provided at the end of this exercise.
10. If desired, ask your instructor to activate another fault. Troubleshoot the new
fault using another Troubleshooting Worksheet.
11. When you have finished using the system, exit any software being used and
turn off the equipment.
CONCLUSION
This exercise has allowed you to improve your knowledge of troubleshooting
techniques. You learned how to apply the Troubleshooting Procedure, outlined in
the first exercise of this unit, to the Earth Station Receiver.
REVIEW QUESTIONS
1. When troubleshooting, it is essential to ensure that all instruments used for
signal observation and measurement are operating correctly. What could be
the result of using a malfunctioning RF power meter when troubleshooting a
satellite communication system?
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Ex. 4-2 – Troubleshooting the Earth Station Receiver  Review Questions
2. Digital demodulation requires recovery of the clock signal. What effect would
a defective clock recovery circuit have on the demodulation of digital signals.
3. If the carrier signal is not successfully recovered, what effect would this have
on the recovered data?
4. What is the usefulness of an RF power meter when troubleshooting a
communications system?
5. Is it necessary to verify all output channels of a TDM DEMUX?
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Ex. 4-2 – Troubleshooting the Earth Station Receiver  Troubleshooting Worksheet
TROUBLESHOOTING WORKSHEET
Student’s Name:
________________________________________________________________
Instructor’s Name:
________________________________________________________________
Fault:*
________________________________________________________________
Troubleshooting Procedure:
1.
Identify the defective module(s) or mode(s) and check visually for damage.
2.
Verify that power supplied to all modules. Note all status LEDs and other indicators.
3.
Apply the appropriate signals and use signal flow tracing to locate the problem.
4.
Verify any other input branch, if present.
5.
Make sure the malfunction located plausibly explains the problem observed.
6.
Diagnose the problem.
Problem Description and Symptoms: ________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
Defective circuit: ________________________________________________________________________
______________________________________________________________________________________
Diagnosis: _____________________________________________________________________________
______________________________________________________________________________________
Instructor’s Comments: ___________________________________________________________________
______________________________________________________________________________________
Notes: ________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
* At instructor’s discretion
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