“150”, Aptitude Test Questions and Answers for Signal and Telecommunication Technician – TRC.
ABSTRACT
This preparation set contains 150 challenging multiple-choice questions and answers designed for candidates preparing for the Signal & Telecommunication Technician II position at Tanzania Railways Corporation (TRC). The questions cover railway signalling, interlocking, train control, fibre-optic communication, radio communication, telecommunications, electrical and electronic fundamentals, network systems, maintenance, troubleshooting, safety, technical reporting, project planning, quantity estimation and cost calculations. The questions are structured to test both technical knowledge and practical application through realistic railway-based scenarios, calculations and closely related answer choices, helping candidates develop the technical reasoning, accuracy and problem-solving skills required for a competitive aptitude assessment.
Prepared by Signal and Telecommunication Technician
– TRC.
Compiled by Signal and Telecommunication Technician
– TRC.
0628729934.
Date: September 27, 2026
Dear applicants,
This collection of questions and answers
has been prepared to help all of you to understand the key areas tested during
the interview. The goal is to provide a useful, and practical study guide so
you can all perform confidently and fairly in the selection process. I wish you
the best of luck, and may this resource support you in achieving success!
Warm regards,
Signal and Telecommunication Technician – TRC.
For Personal Use by Applicants Preparing
for Signal and Telecommunication Technician – TRC - at Public Service
Recruitment Service.
Signal and Telecommunication
Technician – TRC.
150 Aptitude
Test Questions and Answers
1. A railway
signalling system is designed so that when a critical component fails, the
resulting condition prevents an unsafe train movement rather than permitting
normal operation. Which principle is being applied?
A. Redundant
transmission B. Fail-safe operation C. Preventive maintenance D. Automatic
restoration
Answer: B.
Fail-safe operation
Rationale: Fail-safe operation is a fundamental
principle in railway signalling because signalling systems are safety-critical.
The system is designed so that a failure, loss of power, broken circuit, or
loss of communication tends to produce the safest practical condition, normally
a restrictive indication or prevention of an unsafe route. Redundancy may
improve availability, while preventive maintenance reduces failures, but
neither describes the specific safety philosophy in which a failure results in
a safe state.
2. A
technician measures the optical power at the transmitter of a fibre-optic
railway link and finds it normal. At the receiving end, however, the optical
power is substantially lower than expected. Which investigation would most
directly help identify the location and magnitude of losses along the fibre?
A. Measuring
battery terminal voltage B. Testing radio modulation depth C. Performing an
OTDR measurement D. Checking the relay contact resistance
Answer: C.
Performing an OTDR measurement
Rationale: An Optical Time-Domain Reflectometer
(OTDR) sends optical pulses into a fibre and analyses returned reflections to
determine the location and magnitude of events such as excessive attenuation,
connectors, splices, bends and breaks. This makes it particularly useful when a
technician needs to identify where along a railway fibre route a problem has
occurred. Battery voltage, radio modulation and relay resistance may be
relevant to other systems but cannot locate optical losses along the fibre.
3. A railway
interlocking system is required to ensure that a train movement can only be
authorized when the necessary route conditions are satisfied. Which condition
is the interlocking primarily intended to prevent?
A. Instability in
railway equipment power supplies B. Excessive attenuation across transmission
links C. Loss of capacity in communication channels D. Incompatible routes
being established simultaneously
Answer: D.
Incompatible routes being established simultaneously
Rationale: An interlocking system prevents
incompatible or conflicting train routes from being established simultaneously
by enforcing predefined safety conditions before a route can be authorized.
Depending on the signalling architecture, these conditions can include route
availability, correct point position and locking, track occupancy and other
required dependencies. The primary purpose is therefore to prevent unsafe
combinations of train movements rather than to control communication bandwidth,
optical attenuation or general power-supply performance.
4. A
fibre-optic cable has an attenuation of 0.25 dB/km. If a railway communication
link contains 24 km of fibre, excluding connector and splice losses, what is
the approximate fibre attenuation?
A. 4.8 dB B. 5.2
dB C. 6.0 dB D. 6.8 dB
Answer: C. 6.0
dB
Rationale: Fibre attenuation is calculated by
multiplying attenuation per kilometre by the fibre length. Therefore, 0.25
dB/km × 24 km = 6.0 dB. The calculation excludes additional losses from
connectors, splices, bends and other components because the question specifically
asks for fibre attenuation alone. The other values result from using an
incorrect attenuation factor or arithmetic.
5. A
technician is troubleshooting a railway communication system. The equipment
powers up normally, but communication with the control centre is unavailable.
Local diagnostic indicators show that the communication interface is
operational. Which fault should be investigated first?
A. The external
transmission path B. The remote application configuration C. The local
equipment power supply D. The equipment cooling arrangement
Answer: A. The
external transmission path
Rationale: If the equipment has normal power and its
local communication interface indicates normal operation, attention should
first move toward the path connecting the equipment to the remote system.
Depending on the network architecture, this may include fibre, copper, radio,
switches, connectors or intermediate transmission equipment. The remote
application and environmental conditions can also cause communication problems,
but the confirmed local status makes examination of the transmission path an
appropriate first diagnostic step.
6. A
conventional track circuit detects a train when its wheelsets enter an
energized section of track. Which electrical effect normally causes the
detection system to recognize the section as occupied?
A. Opening the
electrical path between the rails B. Providing a low-resistance path between
the rails C. Increasing the applied track-circuit frequency D. Disconnecting
the track relay from the circuit
Answer: B.
Providing a low-resistance path between the rails
Rationale: In a conventional track circuit, the
rails form part of an electrical detection circuit. When a train enters the
section, its wheelsets and axles provide a relatively low-resistance electrical
path between the two rails, altering the electrical condition of the circuit
and causing the associated relay or electronic detector to indicate occupancy.
The precise circuit arrangement varies between signalling systems, but the
essential principle is that the train changes the electrical state of the track
circuit.
7. A railway
fibre link has a transmitter output of +2 dBm and the measured receiver input
is −10 dBm. Ignoring any equipment margins, what is the approximate total loss
of the link?
A. 8 dB B. 10 dB C.
12 dB D. 14 dB
Answer: C. 12
dB
Rationale: Link loss is determined from the
difference between transmitted and received optical power expressed in dBm.
Therefore, +2 dBm − (−10 dBm) = 12 dB. The negative receiver value means the
receiver is receiving less power than the transmitter output, and the
difference represents the total loss across the link. This type of calculation
is useful when checking whether measured fibre performance is consistent with
the expected link budget.
8. During
maintenance, a technician discovers that a railway signal remains at its
restrictive aspect even though the operator has requested a route that would
normally permit a less restrictive indication. Which approach is most
appropriate before replacing signalling equipment?
A. Replace the
signal immediately B. Bypass the interlocking temporarily C. Investigate the
relevant safety conditions D. Reset every system without inspection
Answer: C.
Investigate the relevant safety conditions
Rationale: A restrictive signal may be the correct
result of an unresolved safety condition rather than a failed signal itself.
The technician should systematically establish whether the track section is
occupied, points are correctly positioned and locked, the route is available,
required detection circuits are healthy, and communication or control
conditions are satisfied. Replacing equipment without diagnosis or bypassing
interlocking would be unsafe because they could defeat protections intended to
prevent an unsafe train movement.
9. A radio
communication system operates at 450 MHz. Approximately what is the wavelength
of the radio signal in free space?
A. 0.33 m B.
0.67 m C. 1.50 m D. 2.25 m
Answer: B.
0.67 m
Rationale: Wavelength is calculated using λ = c/f,
where c is approximately 3 × 10⁸
m/s and f is 450 × 10⁶ Hz. Therefore, λ ≈
3 × 10⁸
/ 450 × 10⁶ = 0.667 m, or approximately 0.67 m. This
relationship is important when considering radio propagation, antenna
dimensions and communication-system design.
10. A railway
communication cabinet experiences repeated equipment resets whenever the main
electrical supply becomes unstable. The equipment has a backup battery, but the
resets continue. Which part of the system should be investigated first?
A. The backup
power switching and DC supply path B. The fibre cable jacket and
identification markings C. The cabinet ventilation label and equipment
nameplate D. The external antenna mounting arrangement
Answer: A. The
backup power switching and DC supply path
Rationale: If equipment resets continue despite the
presence of a backup battery, the technician should investigate whether the
battery is actually being connected to the load correctly and whether the
transfer, charger, DC distribution, protection or associated power path is
functioning properly. A backup battery does not guarantee uninterrupted
operation if the switching or distribution system is defective. The other
options do not directly explain resets associated with instability of the
primary electrical supply.
11. A
technician is preparing a fibre-optic link budget for a railway project. The
fibre contributes 4 dB of loss, connectors contribute 2 dB, splices contribute
1 dB, and the design requires a 3 dB engineering margin. What minimum total
allowance should be considered?
A. 7 dB B. 8 dB C.
9 dB D. 10 dB
Answer: D. 10
dB
Rationale: The total link budget allowance must
include all stated losses and the required engineering margin. Therefore, 4 dB
fibre loss + 2 dB connector loss + 1 dB splice loss + 3 dB margin = 10 dB. The
margin is important because real systems can experience variations caused by
ageing, temperature, additional handling, connector degradation and other
factors. Omitting the margin would underestimate the required optical power
budget.
12. An
electronic railway system receives correct data from a field device, but the
control centre displays the information several seconds late. Which parameter
is most directly associated with this problem?
A. Transmission
latency B. Conductor resistance C. Battery capacity D. Antenna polarization
Answer: A.
Transmission latency
Rationale: Latency is the time taken for information
to travel through a communication system from source to destination. Excessive
latency may result from transmission equipment, network congestion, processing,
routing, buffering or other network conditions. While resistance, battery
capacity and antenna polarization can affect other aspects of system
performance, they do not directly describe the delay between sending and
receiving valid information.
13. A railway
technician needs to determine whether a copper communication cable has an open
circuit before reconnecting it to operational equipment. Which instrument is
most appropriate for a basic continuity test?
A. Optical power
meter B. Multimeter C. Spectrum analyser D. OTDR
Answer: B.
Multimeter
Rationale: A multimeter can be used in continuity or
resistance mode to establish whether an electrical conductor provides a
continuous path. This is an appropriate first-level test for a copper cable
suspected of being open-circuit. An OTDR is intended primarily for optical
fibre, while an optical power meter measures optical power and a spectrum
analyser examines signal characteristics over frequency. The correct instrument
therefore depends on the physical medium and fault being investigated.
14. A railway
signalling circuit uses a relay whose contacts change state when its coil is
energised. What is the primary function of such a relay in a conventional
control circuit?
A. Convert light
into data B. Provide controlled electrical switching C. Increase fibre
transmission distance D. Measure radio frequency deviation
Answer: B.
Provide controlled electrical switching
Rationale: An electromechanical relay uses an
electrically energised coil to operate contacts, allowing one circuit to
control another circuit electrically. Relays have historically been important
in railway signalling because their defined contact states can be incorporated
into logic and interlocking circuits. They do not inherently convert optical
signals, extend fibre distance or measure radio-frequency deviation.
15. During
inspection of an underground railway communication cable, a technician finds
that the cable insulation has deteriorated and moisture has entered the cable
route. Which consequence is most likely to require immediate technical
attention?
A. Increased
electrical leakage B. Reduced label visibility C. Increased cabinet height D.
Reduced rail gauge
Answer: A.
Increased electrical leakage
Rationale: Moisture entering a deteriorated cable
can reduce insulation resistance and create leakage paths between conductors or
between conductors and earth. This can cause communication errors,
interference, equipment malfunction and potentially unsafe electrical
conditions depending on the circuit. The condition therefore requires technical
investigation and corrective action. The other listed effects are unrelated to
the electrical consequences of moisture penetration.
16. A
train-control communication channel becomes unavailable while a train is
approaching a controlled section. From a railway safety perspective, which
response is most appropriate?
A. Permit normal
movement automatically B. Ignore the communication failure temporarily C.
Apply the prescribed safe failure procedure D. Increase train speed to clear
the section
Answer: C.
Apply the prescribed safe failure procedure
Rationale: Train-control and signalling systems are
safety-critical, so loss of communication must be handled according to the
approved operating and technical failure procedure. The appropriate response
depends on the specific signalling and train-control architecture, but it
should preserve safe separation and prevent an unauthorised movement.
Automatically permitting normal movement or increasing speed would undermine
the purpose of the safety system.
17. A
fibre-optic technician observes that the optical loss increases significantly
whenever a particular section of cable is sharply bent. Which physical
phenomenon most likely explains the observation?
A.
Bending-induced optical loss B. Increased electrical resistance C. Reduced
radio modulation D. Transformer saturation
Answer: A.
Bending-induced optical loss
Rationale: Excessive bending can cause optical
energy to escape from the fibre's guided mode, producing additional
attenuation. The severity depends on fibre type, bend radius, wavelength and
cable construction. This is why fibre installations must observe manufacturer-specified
minimum bend radii. Electrical resistance, radio modulation and transformer
saturation are not the direct mechanisms responsible for optical loss caused by
bending a fibre.
18. A
technician is asked to prepare a quantity and cost estimate for installing a
new communication cable along a railway route. Which information is most
essential for establishing the material quantity?
A. Colour of the control-room walls B.
Technician's preferred equipment brand C. Number of railway passengers per day D.
Cable route length and installation requirements
Answer: D.
Cable route length and installation requirements
Rationale: A meaningful quantity estimate requires
the physical scope of work, including route length, cable type, installation
method, protection requirements, joints, termination points and relevant
allowances. These determine how much cable and associated material will be
required. Passenger numbers may be useful for broader planning but do not
directly establish cable quantity, while personal brand preference and wall
colour are irrelevant to the material calculation.
19. A railway
communication system has a nominal data rate of 2 Mbps. Which statement best
describes the meaning of this value?
A. Two million
signal cycles per second B. Two million bits transmitted per second C. Two
million bytes transmitted per second D. Two million packets transmitted per
second
Answer: B. Two
million bits transmitted per second
Rationale: Mbps means megabits per second and
describes a data rate of approximately two million bits per second under the
stated nominal value. A bit is not the same as a byte; one byte consists of
eight bits. Similarly, packet rate depends on packet size and network
conditions, while signal frequency is a separate physical characteristic.
Correctly distinguishing bits, bytes, packets and frequency is essential in
telecommunications.
20. A railway
technician measures a 24 V DC circuit and finds a load drawing 3 A. Assuming
the load behaves normally, what is its approximate electrical power?
A. 8 W B. 27 W C.
72 W D. 96 W
Answer: C. 72
W
Rationale: Electrical power in a DC circuit is
calculated using P = V × I. Therefore, P = 24 V × 3 A = 72 W. The result
represents the approximate power consumed by the load under the stated
conditions. The other values arise from using an inappropriate arithmetic relationship
between voltage and current.
21. During an
accident investigation involving a signalling failure, the technical team
discovers that an equipment alarm had appeared several hours before the
incident but was not acted upon. What should the investigation primarily
establish regarding this information?
A. Whether the
alarm was technically relevant to the subsequent event B. Whether the alarm
had been acknowledged by the operating staff C. Whether the alarm occurred
during a period of scheduled maintenance D. Whether the alarm originated from
the same equipment involved in the failure
Answer: A.
Whether the alarm was technically relevant to the subsequent event
Rationale: Accident investigation should establish
the sequence of events, technical conditions, alarms, failures, responses and
contributing factors. An earlier alarm may provide important evidence if it was
associated with the eventual failure, but investigators must establish its
technical relevance rather than automatically assuming that it caused the
incident. Other information such as acknowledgement, maintenance timing and
alarm origin may also assist the investigation, but the primary question is
whether the warning has a demonstrable technical relationship to the event.
22. A digital
railway communication system transmits a binary sequence, but interference
causes the receiver to interpret some transmitted 1s as 0s. Which communication
problem has occurred?
A. Frequency
drift B. Packet duplication C. Transmission latency D. Bit error
Answer: D. Bit
error
Rationale: A bit error occurs when the value
received differs from the value that was transmitted. In this case,
interference causes the receiver to interpret a transmitted binary 1 as 0,
which is directly a bit error. Noise, interference, attenuation and distortion
can contribute to bit errors by reducing the receiver's ability to distinguish
between the intended signal states. Packet duplication, latency and frequency
drift describe different communication problems.
23. A railway
signal installation uses two independent power sources so that failure of one
source does not immediately interrupt the critical system. Which engineering
objective is primarily being achieved?
A. Increased
system redundancy B. Reduced transmission latency C. Improved signal
modulation D. Increased circuit operating frequency
Answer: A.
Increased system redundancy
Rationale: Redundancy involves providing additional
components, paths or resources so that a system can continue performing its
required function when one element fails. Providing independent power sources
is an example of redundancy intended to improve system availability and
resilience. Redundancy must nevertheless be properly designed so that common
points of failure do not defeat the intended protection and so that failures do
not introduce unsafe conditions.
24. A
technician is inspecting a railway radio installation and finds that the
transmitter output is normal when tested directly at the equipment, but the
signal received at the remote station is weak. Which part of the system should
be investigated first?
A. The equipment
cabinet colour B. The technician's identity card C. The transmission path and
antenna system D. The railway timetable format
Answer: C. The
transmission path and antenna system
Rationale: If transmitter output is confirmed to be
normal at the equipment, a weak signal at the remote station suggests that the
problem may lie in the transmission path, feeder, connectors, antenna,
propagation environment or receiving side. A systematic investigation should
therefore examine those components before replacing a transmitter that has
already demonstrated normal output. This approach avoids unnecessary
replacement and follows sound fault-isolation practice.
25. A railway
communication project requires a technical report after completion of
maintenance work. Which combination would provide the most useful engineering
record?
A. Work
performed, findings, measurements and recommendations B. Work location,
personnel involved, equipment age and maintenance duration C. Equipment
condition, environmental observations, photographs and operator comments D.
Fault description, corrective action, material usage and work completion date
Answer: A.
Work performed, findings, measurements and recommendations
Rationale: A technical maintenance report should
provide an objective record that allows supervisors and future technicians to
understand what was done, what was discovered, what measurements or tests were
obtained, what equipment condition was established, and what further action is
recommended. Other information such as location, personnel, environmental
observations, materials and completion dates may also be useful, but a
technically meaningful report must contain verified findings and measurements
together with the work performed and resulting recommendations.
26. In a
railway signalling installation, a point machine has moved the turnout toward
the requested position, but the detection circuit does not confirm that the
point has reached and locked the required position. What should the signalling
system normally do?
A. Permit the
route after a time delay B. Indicate the route as safely established C.
Prevent the route from being cleared D. Increase the signal transmission power
Answer: C.
Prevent the route from being cleared
Rationale: A signalling system should not regard a
route as safely established merely because a point machine has been commanded
to move. The system must receive reliable detection that the points have
reached the required position and, where applicable, are properly locked. If
detection is absent or contradictory, the safe response is to prevent the
relevant route from being cleared. This protects against a train being directed
over points whose actual position has not been safely confirmed.
27. A
technician is comparing single-mode and multimode fibre for a long-distance
railway communication backbone. Which characteristic generally makes
single-mode fibre more suitable for such a link?
A. Lower modal
dispersion B. Larger optical core C. Higher electrical conductivity D.
Simpler copper termination
Answer: A.
Lower modal dispersion
Rationale: Single-mode fibre has a much smaller core
and allows essentially one propagation mode, greatly reducing modal dispersion
over long distances. This permits higher bandwidth and longer transmission
distances than conventional multimode fibre. Multimode fibre has a larger core
and supports multiple propagation modes, making it useful for shorter links but
more susceptible to modal dispersion. Neither fibre type relies on electrical
conductivity for optical transmission.
28. A railway
control network uses IP-based equipment. A technician can successfully ping a
field device, but the control application cannot exchange the required
operational data with that device. Which interpretation is technically most
appropriate?
A. IP
connectivity is available, but a higher-layer service or configuration may be
preventing data exchange B. Successful ping proves that all application ports
and services are operating correctly C. The communication medium must be
physically disconnected because application data is unavailable D. The device
cannot participate in the network because an IP address is responding to the
test
Answer: A. IP
connectivity is available, but a higher-layer service or configuration may be
preventing data exchange
Rationale: A successful ping provides evidence that
basic IP-level communication is functioning, but it does not establish that the
required application service, port, protocol, firewall rule or application
configuration is operating correctly. The fault may therefore exist above the
basic connectivity layer. This distinction is important in railway control
networks because network reachability and successful application-level
communication are separate diagnostic conditions.
29. A 48 V DC
railway telecommunications load draws 2.5 A continuously. Approximately how
much power does the load consume?
A. 96 W B. 108 W C.
120 W D. 144 W
Answer: C. 120
W
Rationale: DC electrical power is calculated using P
= V × I. Therefore, P = 48 V × 2.5 A = 120 W. This calculation is important
when assessing power supplies, battery systems and backup capacity for
telecommunications equipment. The other values result from incorrect
multiplication or from using an inappropriate relationship between voltage and
current.
30. A railway
fibre link develops intermittent errors whenever heavy maintenance activity is
conducted close to the cable route. Previous optical measurements taken when
the route was undisturbed were within specification. Which condition should be
investigated first?
A. Mechanical
stress, bending or disturbance of the fibre route B. A change in the nominal
operating frequency of an unrelated radio channel C. The colour identification
scheme used on signalling equipment D. The physical height of nearby signal
posts
Answer: A.
Mechanical stress, bending or disturbance of the fibre route
Rationale: The correlation between maintenance
activity and intermittent fibre errors makes physical disturbance an important
suspect. Bending, crushing, pulling or vibration can temporarily or permanently
increase optical attenuation, even where earlier measurements were
satisfactory. The investigation should therefore examine the cable route,
protection, bends, joints and other locations that may have been mechanically
disturbed.
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