ETM3086 Mobile and Satellite Communications
MSC1
FACULTY OF ENGINEERING
LAB SHEET
MOBILE AND SATELLITE
COMMUNICATIONS
ETM 3086
TRIMESTER I (2012/2013)
MSC1: Testing of Mobile Radio
At Telecommunications Lab AR4022
All students are expected to read through the manual before attending this laboratory session.
Please bring along the print out that illustrate the use of network analyser
ETM3086 Mobile and Satellite Communications
MSC1
EXPERIMENT MSC1
TESTING OF MOBILE RADIO
1.0
OBJECTIVES
 To understand the importance of the following mobile radio tests: transmit power; transmit
frequency, modulation characteristics, audio frequency (AF) bandwidth tests, and harmonic
analysis.
 To acquire the technical skill in measuring the power of a transmitted radio signal.
 To acquire the technical skill in measuring the frequency of a transmitted radio signal.
 To acquire the technical skill in measuring the modulation parameters of a transmitter.
 To acquire the technical skill in measuring the AF bandwidth of a radio transmitter.
 To acquire the technical skill in making harmonic analysis at radio frequency (RF) range.
2.0
INTRODUCTION
To study the functionality of a mobile radio transceiver as per recommended specifications, it is
necessary to check the performance of both transmitter and receiver. The number and type of tests
carried out on a radio transceiver depend on whether development, manufacturing or servicing of
the radio are being carried out. The tests proposed in this experiment are those normally used to
check the performance of a mobile radio that is within the set limits, which are stipulated by
appropriate regulatory bodies of the country.
Transmitter testing is carried out by modulating the transmitter with an audio source usually an 1kHz tone. The signal is then captured for analysis with something that emulates the receiver. The
instrument normally used for this function is a modulation meter.
In the receiver testing, the receiver requires some form of signal source which emulate a transmitter.
Once the receiver has demodulated the RF signal to produce an audio signal, various tests on the
audio output will be conducted to study the performance of the receiver. The instrument normally
used for this purpose is an audio power meter, possibly incorporating a switch-able 1 kHz notchfilter, or a distortion factor meter.
In general, some of the In-Band tests and experiments which can be conducted are:
 Transmitter Testing:
Transmitter Power Output, Transmitter Frequency, Modulation
Characteristics, Modulation Frequency Response / AF Bandwidth, Modulation Distortion, Hum
and Noise.
 Receiver Testing: SINAD Sensitivity, Quieting Sensitivity, Signal to Noise (S/N), Sensitivity,
and Audio Frequency Bandwidth.
Other tests and experiments, especially Out-of-Band tests which can be implemented are:
 Transmitter Testing: Spurious emission measurement, supply voltage variation test.
 Receiver Testing: Selectivity, inter-modulation and blocking (desensitization), spurious
response, image frequency rejection, AGC response, supply voltage variation tests.
In this experiment, you are required to conduct the following tests:
Transmit Power Test
The maximum allowable transmit power of a mobile device is governed by local regulatory body.
Excessive transmit power may cause adjacent channel interference to other devices or health related
problems.
Transmit Frequency Test
ETM3086 Mobile and Satellite Communications
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The frequency at which the transmitter operates (i.e. the carrier frequency) is an important
parameter for the following reasons:
 If the transmitter is not operating at the desired frequency, interference with other transmission
channels will be resulted.
 If the transmitter frequency is slightly deviated, the receiver may receive an apparently distorted
signal. (i.e. frequency matching between the transmitter and receiver is essential for proper
operation of the radio channel.)
Modulation Characteristics Test
This test is preformed to investigate the consequences of over modulation in the transmitter. If a
transmitter is allowed to over-modulate it may cause interference to other users. Over-modulation
is caused by incorrect gain settings at the output stages of the transmitter, extending the amount of
modulation for large amplitudes of the modulating signal to a level for which the system is not
designed. When a transmitted signal is over-modulated, the frequency spectrum of the modulated
signal will expand beyond the allocated occupancy and could cause interference to other receivers.
Audio Frequency Bandwidth Test
This test measures the audio frequency bandwidth of the transmitter modulator circuits.
If the audio frequency bandwidth is too narrow, the listener who is receiving the signal will have
great difficulty in determining what is being broadcasted due to the limited audio frequency range.
On the other hand, the audio frequency bandwidth is too wide; there will be few detrimental or
beneficial effects to the received transmission, because the receiver will still be configured to the
normal, narrower audio bandwidth. Thus, a wide audio bandwidth transmission will restrict the
number of adjacent channels that can be used.
RF Harmonic Analysis
The harmonic content of a transmitter output can be analyzed using the harmonic analyzer function.
ETM3086 Mobile and Satellite Communications
LEVEL
dB
MSC1
0 dB
Rx
3 dB
WHAT RECEIVER
ACCEPTS
f
LEVEL
dB
AUDIO FREQUENCY BANDWIDTH
TOO NARROW
f
AUDIO FREQUENCY BANDWIDTH
TOO WIDE
LEVEL
dB
f
Fig.: (Top):
(Middle)
(Bottom)
Correct Receiver Audio Bandwidth
Compressed Transmitter Audio Bandwidth
Expanded Transmitter Audio Bandwidth
3.0
EQUIPMENT LIST
 1 unit of BNC to BNC RF connector
 1 unit of Motorola GP300 walkie-talkie with battery fully charged
 1 unit of Communications Service Monitor CSM2945A
 1 unit of Motorola Portable Radio Test Set, RTX-4005B
 1 unit of 13.8V power supply for GP300 walkie-talkie
4.0
PREPARATION
 Fully Charged battery (by Lab Technician)
 Read the lab sheet. Conduct background study about the experiment.
 Bring the followings: a log book for recording observations and results, a scientific
calculator, and graph papers.
5.0
REFERENCES
 Marconi Instrument, “Communications Service Monitor 2945A Operating Manual”.
 Motorola Test Equipment: Portable Radio Test Set RTX-4005B Manual
ETM3086 Mobile and Satellite Communications
6.0
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PROCEDURES
6.1 Transmitter Test Setup
In principle, the Communications Service Monitor (CSM2945A) generates an AF signal that
goes into a mobile radio (Motorola GP300 walkie-talkie), which performs frequency modulation
(FM) and then transmits the signal in the RF range. The RF signal is then fed into the
CSM2945A unit for analysis.
1. Connect the RF connector to the GP300 walkie-talkie. Connect (with RF test cable) the
CSM2945A ‘RF I/O’ port to RF connector on the walkie-talkie. The I/O port must be
configured as an Input port (by pressing the SELECT button).
2. Connect the service cable from GP300 microphone / speaker jack to "Service Cable" receptor
on the Portable Radio Test Set RTX-4005B. Make sure the jack is inserted fully.
3. Connect (with BNC to crocodile clip cable) ‘AF Gen Out’ port of CSM2945A to ‘Audio In’
port of Portable Radio Test Set RTX-4005B.
4. Place the meter selector of the Interface Unit RTX-4005B to MIC position.
5. Use a fully charged battery to power the GP300 walkie-talkie, or alternately connect the 13.8V
power supply to walkie-talkie.
6. Press the [Tx TEST] button on the CSM2945A. It is now in ‘Auto Tune’ mode now by default.
[Tx Freq] > [Auto Tune]
7. Apply 550 mV, 1 kHz tone from ‘AF Gen Out’ port of the CSM2945A. [Audio Gen] > [FREQ]
1 [kHz] > [LEVEL] 550 [mV]
8. [Tx TEST] > [Audio Gen] > [Gen 1/Gen 2] allows you to switch between AF1 and AF2. Use
only AF1. Select AF2, turn it off by pressing the [ON/OFF] button.
Transmitter Test Setup
___________________________________________________________
CSM 2945A
________________________
|
|
| AF GEN
|
| OUT AF INPUT RF IN/OUT |
|
o
o
o
|
|__________________|
MIC/SPK JACK

RF CONN

________________________________
__________________
| o o
o o
O |
| AC/DC AUDIO Service Cable |
| Mtr
IN
Receptacle |
|
|
|__________________|
|
13.8V
|
| Power Supply |
|__________|
GP300
walkie-talkie


RTX-4005B
___________________________________________________
ETM3086 Mobile and Satellite Communications
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6.2 Experimental Procedures
6.2.1 Transmit Power Measurement
a) Switch on the walkie-talkie and select a channel (say, Channel 1).
b) At AF signal level as high as 550 mV, the walkie-talkie transmits immediately once you turn it
on (as indicated by its red LED being ON). At this point, if its LED remains OFF, it shows that
the battery has depleted. Replace the battery or use the 13.8V power supply instead.
c) Observe that the CSM unit quickly tunes to the transmitted signal and it records a stable value
of transmission power.
d) Press the [DISPLAY HOLD] button to freeze the display.
e) Turn off the walkie-talkie.
Precaution: The walkie-talkie may be overheated if it being keeps transmitting. Turn it on only
when taking measurement data. Otherwise, turn it off.
f) Record the Transmit (Tx) Power of the mobile radio (i.e. walkie-talkie).
Tx Power: ____________ dBm
Attention: Throughout the experiment, if the Tx Power drops to a very low level (say, < 15 dBm),
that means the battery runs out of power. Replace the battery or use the 13.8V power supply to
power up the walkie-talkie.
6.2.2 Transmit Frequency Measurement
a) Record the Transmit (Tx) Frequency.
Tx Frequency: _____________ MHz
b) Press the [DISPLAY HOLD] button again to release the display.
c) To measure the Tx Frequency Offset from the initial recorded value, enter the reference
frequency of the walkie-talkie by selecting the [Tx Freq] function. (If you do not key in any
value, the Tx FREQ value at the moment you select the [Tx Freq] function is taken as the initial
recorded value.)
d) Press the [DISPLAY HOLD] button to freeze the display.
e) Record the Tx Frequency Offset. Comment the significance of the recorded value.
Tx Frequency Offset: ________________ Hz
f) Select the [Print] function to print your result. Make sure the printer is set to “ON LINE” mode
before you start printing.
g) Press the [DISPLAY HOLD] button again to release the display.
h) Select the [Auto Tune] function again.
6.2.3 Modulation Characteristics (vary Am while fm is fixed)
a) Keep the existing experimental setup.
b) In frequency modulation (FM), the frequency deviation varies with the amplitude (Am )and
frequency (fm) of the modulating signal
To investigate the modulation characteristic of the radio transmitter, the frequency of the
modulating signal is fixed at a constant value while varying the amplitude of the modulating
signal. Observe the changes in frequency deviation.
Explain the type of signal that serves as the input to the walkie-talkie and modulates the carrier.
Identify its range of frequency.
c) Choose a frequency of the modulating signal frequency that is representative of the above range
of frequency.
ETM3086 Mobile and Satellite Communications
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d) Now vary the modulating signal amplitude and observe the changes in frequency deviation as
recorded in the CSM2945A unit. Comment on your observation.
To adjust the modulating signal level, you may follow these steps: [Tx TEST] > [Audio Gen] >
[Gen 1/Gen 2] > [LEVEL].
Note: When the AF Gen level reduces to lower than approximately 220 mV, the walkie-talkie
may cease transmission (the LED on the walkie-talkie turns off). In this case, press the push-totalk button to initiate the transmission (the LED will turn on).
To observe the level of frequency deviation, you may follow these steps: [Mod Meter] >
[More] > [FM Dev Pk / rms], choose ‘Pk’.
It is necessary to choose the appropriate cutoff frequencies for the AF filter and the intermediate
frequency (IF) filter used in the CSM2945A, by following these steps:
[Mod Meter] > [AF Filter] > Choose an appropriate value
[Mod Meter] > [IF Filter] > Choose a value larger than the cutoff frequency you set for the
[AF Filter]
Justify your choices.
e) Prove/Show that the CSM2945A unit successfully demodulates the radio signal transmitted
from the walkie-talkie.
Hint: You can view the demodulated signal on the scope by selecting [Scope/Bar] function,
which toggles between three different views: a power meter (bar chart display), a scope
(standard display), and a larger scope (expanded display). Print out the result to prove your
case.
f) Based on your observation above, specify the amplitude of modulating signal, beyond which
distortion might be experienced. Show your proof.
g) Identify the maximum frequency deviation.
6.2.4 Audio Frequency Bandwidth(vary fm while Am is fixed)
a) Keep the existing experimental setup as before.
b) Now we want to examine the range of audio frequencies, which is acceptable to the walkietalkie. This test is conducted by keeping the amplitude of modulating signal at a fixed value
while varying the frequency of the modulating signal frequency and observing the frequency
deviation as measured by the CSM2945A unit.
c) Choose an appropriate amplitude level of modulating signal.
d) Choose an appropriate range of the modulating signal frequency to be examined. Explain your
choice.
Note: You may need to reselect the cutoff frequencies for the AF and IF filters used in the
CSM2945A unit.
e) Now vary the modulating signal frequency within the selected range, and observe the changes
in the recorded frequency deviation. Plot the frequency deviation versus modulating signal
frequency on a graph to illustrate their relationship. Explain your observation.
f) Based on your observation, conclude on the audio frequency range that is acceptable to the
walkie-talkie. Justify your conclusion.
Alternative: There is more than one way to conclude on the acceptable bandwidth of the modulating
signal. The following is one possible alternative:
ETM3086 Mobile and Satellite Communications
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Choose an appropriate modulating signal frequency. The resulting frequency deviation will
serve as a reference by setting the following: [Mod Meter] > [More] > [Mod dBr]. The
measurement unit of the frequency deviation now becomes ‘dBr’.
Now decreasing the modulating signal frequency slowly and observe the changes in the
frequency deviation (in ‘dBr’). Continue decreasing until the frequency deviation reaches -3
dBr. Record this modulating signal frequency value. This is the lower cutoff point of the
acceptable bandwidth. Also known as the lower sideband.
Now increasing the modulating signal frequency slowly and observe the changes in the
frequency deviation (in ‘dBr’). Continue increasing until the frequency deviation reaches -3 dBr.
Record this modulating signal frequency value. This is the upper cutoff point of the acceptable
bandwidth. Also referred to as the upper sideband.
Calculate the modulating signal bandwidth that is acceptable to the walkie-talkie.
6.2.5 RF Harmonic Analysis
a) Select [Tx Power] > [Harmonic Analysis]. The harmonic content of the transmitted signal is
shown on the bar charts. The unit is dB relative to the carrier level (dBc).
b) Explain the meaning of harmonic frequencies and the method of calculation.
c) Identify the number of harmonics you have observed. Explain why the number is not high.
d) Print screen and show it as a proof.
Marking Scheme
Assessment Components
1
Acquisition of the technical skills in using radio test equipment to measure radio
signal power and frequency
2
Reasonable choices in modulating signal level and its range of frequencies in the
investigation of modulation characteristic
3
Correctness in relating and explaining changes in frequency deviation with
respect to modulating signal level and frequency
4
Reasonable settings of AF and IF filter frequency ranges, followed by
justification
5
Proof of demodulated signal
6
Correct identification of the modulating signal level that would cause distortion
7
Reasonable choices in modulating signal frequency and the range of signal levels
in the investigation of the bandwidth acceptable to the mobile radio
8
Reasonable estimation of the bandwidth acceptable to the mobile radio
9
Correct understanding of harmonic frequencies
10 Effectiveness in working as a team to ensure smooth running of the lab session
Total
Marks
10
10
10
10
10
10
10
10
10
10
100
ETM3086 Mobile and Satellite Communications
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Appendix
FM fundemental:
Carrier Signal
c(t )  Ac cos 2f ct
Modulating signal: s(t) = Amm(t)
e.g.
s(t )  Am cos( 2f mt )
Instantaneous frequency fi(t) varies with s(t)
fi(t) = fc + kf Am m(t)
= fc + fvm(t)
Modulation Index:
fv

fm
fv - frequency deviation
fm – frequency of modulating signal
kf - frequency sensitivity (Hz/V)