I85PREP
⌘ K
PSRA Level 1 Exam study materials
PSRA Level 1 Exam study resources

PSRA Level 1 Exam practice questions

One question at a time. Build your PSRA Level 1 Exam understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Radio Frequency Fundamentals and Spectrum Concepts

Which frequency band is conventionally defined as spanning 30 kHz to 300 kHz?

  1. Very low frequency (VLF)
  2. Medium frequency (MF)
  3. Low frequency (LF) Correct answer.
  4. High frequency (HF)

Explanation

In the ITU band plan, LF covers 30 kHz to 300 kHz, with wavelengths of roughly 1 km to 10 km. VLF sits below it (3-30 kHz), while MF (300 kHz-3 MHz) and HF (3-30 MHz) sit above. Each decade step in frequency corresponds to a tenfold change in the band boundary.

Question 2Radio Frequency Fundamentals and Spectrum Concepts

A signal has a frequency of 150 MHz. What is its approximate wavelength in free space?

  1. 2 m Correct answer.
  2. 20 m
  3. 150 m
  4. 0.5 m

Explanation

Wavelength equals the speed of light divided by frequency: 300/150 = 2 meters when using the shortcut lambda (m) = 300 / f (MHz). This shortcut is standard for quick field calculations in the VHF range. Higher frequency always means shorter wavelength for the same propagation medium.

Question 3Radio Frequency Fundamentals and Spectrum Concepts

Which property of an electromagnetic wave is measured in hertz?

  1. Frequency Correct answer.
  2. Phase
  3. Wavelength
  4. Amplitude

Explanation

Frequency counts the number of complete cycles per second and is expressed in hertz. Amplitude describes signal strength, wavelength describes physical distance per cycle, and phase describes position within a cycle. These are independent properties, though they are related by the wave equation.

Question 4Radio Frequency Fundamentals and Spectrum Concepts

What is the primary reason spectrum is regulated and allocated by national administrations?

  1. To reduce the cost of radio hardware
  2. To increase the speed of light in free space
  3. To ensure the physical medium can carry more data
  4. To prevent harmful interference among competing users Correct answer.

Explanation

Radio spectrum is a finite shared resource, so uncoordinated use would produce harmful interference between services. Regulators allocate bands and set technical conditions so that users can coexist. The other options describe physical or economic effects that regulation does not cause.

Question 5Radio Frequency Fundamentals and Spectrum Concepts

Which unit expresses absolute radio frequency power referenced to one milliwatt?

  1. dBc
  2. dB
  3. dBi
  4. dBm Correct answer.

Explanation

dBm is a logarithmic unit of power relative to 1 mW, so 0 dBm equals 1 mW. dBi is antenna gain relative to an isotropic radiator, plain dB is a relative ratio, and dBc is relative to carrier power. The reference suffix is what distinguishes these decibel variants.

Question 6Radio Frequency Fundamentals and Spectrum Concepts

How does bandwidth relate to the range of frequencies a signal occupies?

  1. Bandwidth is the difference between the highest and lowest frequencies occupied Correct answer.
  2. Bandwidth is the time taken for one cycle
  3. Bandwidth is the center frequency of the signal
  4. Bandwidth is the peak power of the signal

Explanation

Bandwidth is the width of the occupied frequency range, calculated as the upper frequency minus the lower frequency. It is distinct from center frequency, which is the midpoint of that range. Wider bandwidth generally supports higher information throughput.

Question 7Radio Frequency Fundamentals and Spectrum Concepts

Which propagation mode allows HF signals to travel beyond the horizon by refracting through the ionosphere?

  1. Sky wave Correct answer.
  2. Ground wave
  3. Tropospheric scatter
  4. Line-of-sight

Explanation

Sky-wave propagation occurs when the ionosphere refracts HF signals back toward the Earth, enabling long-distance communication over the horizon. Ground wave follows the Earth's surface and is limited in range at HF. Tropospheric scatter and line-of-sight rely on lower atmospheric or direct paths.

Question 8Radio Frequency Fundamentals and Spectrum Concepts

What is the relationship between a frequency of 3 MHz and its wavelength in free space?

  1. Wavelength is about 1 meter
  2. Wavelength is about 100 meters Correct answer.
  3. Wavelength is about 1000 meters
  4. Wavelength is about 10 meters

Explanation

Using lambda (m) = 300 / f (MHz), 300/3 gives 100 meters. This places 3 MHz at the boundary between MF and HF. Each tenfold increase in frequency reduces wavelength by a factor of ten.

Question 9Radio Frequency Fundamentals and Spectrum Concepts

A receiver front end has a bandwidth of 20 kHz. What is this bandwidth expressed in hertz?

  1. 2,000 Hz
  2. 200 Hz
  3. 20,000 Hz Correct answer.
  4. 200,000 Hz

Explanation

The prefix kilo means one thousand, so 20 kHz equals 20,000 Hz. Converting between hertz, kilohertz, and megahertz is a simple factor-of-1000 operation. Consistent units are essential when calculating noise power or link budgets.

Question 10Radio Frequency Fundamentals and Spectrum Concepts

Which statement correctly describes the difference between a simplex and a duplex radio channel?

  1. Simplex allows transmission in one direction at a time; duplex supports simultaneous two-way communication Correct answer.
  2. Simplex uses two frequencies for simultaneous two-way traffic; duplex uses one
  3. Simplex is limited to HF; duplex is limited to VHF
  4. Simplex relies on ionospheric reflection; duplex relies on ground wave

Explanation

Simplex operation shares a single path so only one party transmits at a time, while duplex provides simultaneous two-way communication, often using separate uplink and downlink frequencies. This distinction is about channel structure, not the propagation mode or band. Duplex systems are common in mobile networks and repeaters.

Question 11Radio Frequency Fundamentals and Spectrum Concepts

A power level increases from 10 W to 100 W. What is the increase in decibels?

  1. 10 dB Correct answer.
  2. 3 dB
  3. 1 dB
  4. 20 dB

Explanation

A tenfold increase in power equals 10 dB, since dB = 10 log10(P2/P1) = 10 log10(10) = 10. A doubling of power would be about 3 dB, and a hundredfold increase would be 20 dB. Logarithmic decibel values compress large linear ratios into manageable figures.

Question 12Radio Frequency Fundamentals and Spectrum Concepts

Which factor most directly determines the maximum data rate achievable over a given radio channel?

  1. The color of the equipment enclosure
  2. The frequency of the mains supply
  3. The antenna mast height alone
  4. The channel bandwidth and signal-to-noise ratio Correct answer.

Explanation

Shannon's theorem states capacity depends on bandwidth and the signal-to-noise ratio, so both must be considered. Antenna height affects coverage and path loss but is not the direct determinant of capacity. The other options are irrelevant to channel capacity.

Question 13Radio Frequency Fundamentals and Spectrum Concepts

What happens to free-space path loss as the operating frequency increases for a fixed distance and fixed antenna gains?

  1. It remains constant
  2. It becomes zero above 1 GHz
  3. It increases Correct answer.
  4. It decreases proportionally to frequency

Explanation

Free-space path loss grows with frequency because the effective aperture of a fixed-gain antenna shrinks as wavelength shortens. The Friis relationship shows loss rising by 20 log10(f) for a fixed distance. This is why higher bands require more gain or denser infrastructure.

Question 14Radio Frequency Fundamentals and Spectrum Concepts

Which of the following best characterizes the VHF band in the ITU plan?

  1. 3 GHz to 30 GHz
  2. 300 kHz to 3 MHz
  3. 30 MHz to 300 MHz Correct answer.
  4. 3 kHz to 30 kHz

Explanation

VHF spans 30 MHz to 300 MHz, covering services such as FM broadcast, airband, and marine VHF. The band sits between HF and UHF and supports largely line-of-sight propagation. Remembering the decade boundaries helps place any service in the correct band.

Question 15Radio Frequency Fundamentals and Spectrum Concepts

A spectrum analyzer displays a signal centered at 433.92 MHz with a span of 2 MHz. What are the lower and upper displayed frequencies?

  1. 431.92 MHz and 435.92 MHz
  2. 433.92 MHz and 435.92 MHz
  3. 432.92 MHz and 434.92 MHz Correct answer.
  4. 431.92 MHz and 433.92 MHz

Explanation

The span is split evenly around the center frequency, so each edge is 1 MHz from the center. Subtracting and adding 1 MHz to 433.92 MHz gives 432.92 MHz and 434.92 MHz. This is the standard way to set start and stop frequencies from center and span.

Question 16Radio Frequency Fundamentals and Spectrum Concepts

What is the main purpose of a frequency allocation table published by a national regulator?

  1. To define the speed of light for each band
  2. To list which services may use each band and under what conditions Correct answer.
  3. To guarantee interference-free operation for every user
  4. To specify the retail price of radio equipment

Explanation

Allocation tables assign bands to radiocommunication services and set the technical and regulatory conditions for their use. They do not set equipment prices or alter physical constants. Coordination reduces but cannot entirely eliminate interference.

Question 17Radio Frequency Fundamentals and Spectrum Concepts

Two signals at 100 MHz and 101 MHz are transmitted together. What spacing does this represent?

  1. 10 MHz
  2. 1 MHz Correct answer.
  3. 1 kHz
  4. 100 kHz

Explanation

The difference between 101 MHz and 100 MHz is 1 MHz, equal to 1,000 kHz. Channel spacing is commonly specified in kilohertz or megahertz depending on the service. Accurate spacing calculations prevent adjacent-channel overlap.

Question 18Radio Frequency Fundamentals and Spectrum Concepts

Which phenomenon causes a received signal to vary in strength as a mobile station moves through an urban environment?

  1. Frequency allocation
  2. Duplex spacing
  3. Multipath fading Correct answer.
  4. Antenna polarization

Explanation

Multipath fading arises when reflected copies of a signal combine constructively or destructively at the receiver, producing rapid amplitude variation. Allocation and duplex spacing are regulatory or system-design parameters, not propagation effects. Polarization mismatch causes a steady loss rather than location-dependent fading.

Question 19Radio Frequency Fundamentals and Spectrum Concepts

Which decibel value corresponds to halving the power?

  1. -3 dB Correct answer.
  2. -1 dB
  3. -6 dB
  4. -10 dB

Explanation

Halving power gives 10 log10(0.5), which is approximately -3 dB. This rule of thumb is widely used for quick link-budget estimates. A tenfold reduction would be -10 dB, and doubling would be about +3 dB.

Question 20Radio Frequency Fundamentals and Spectrum Concepts

Why is spectrum above roughly 30 GHz often described as having high atmospheric attenuation?

  1. The speed of light decreases sharply above 30 GHz
  2. Absorption by atmospheric gases and water vapor increases at millimeter wavelengths Correct answer.
  3. Antennas cannot be built for those frequencies
  4. Ionospheric reflection becomes stronger at those frequencies

Explanation

At millimeter wavelengths, resonant absorption by oxygen and water vapor becomes significant, producing attenuation peaks near specific frequencies. Ionospheric reflection is negligible at these frequencies, and the speed of light remains essentially constant. Antennas are in fact physically small and practical at these bands.

Question 21Radio Frequency Fundamentals and Spectrum Concepts

A transmitter delivers 0 dBm into a lossless antenna. What power does this represent in milliwatts?

  1. 0.1 mW
  2. 10 mW
  3. 1 mW Correct answer.
  4. 100 mW

Explanation

By definition, 0 dBm equals 1 mW, since dBm is referenced to one milliwatt. Positive dBm values indicate more than 1 mW and negative values less. For example, 10 dBm would be 10 mW and -10 dBm would be 0.1 mW.

Question 22Radio Frequency Fundamentals and Spectrum Concepts

A signal occupies 88 MHz to 92 MHz. Which description of its bandwidth and center frequency is correct?

  1. Bandwidth 4 MHz, center 90 MHz Correct answer.
  2. Bandwidth 92 MHz, center 4 MHz
  3. Bandwidth 2 MHz, center 90 MHz
  4. Bandwidth 4 MHz, center 88 MHz

Explanation

Bandwidth is 92 minus 88, which is 4 MHz, and the center is the midpoint at 90 MHz. This matches the structure of a typical FM broadcast band segment. Confusing center with an edge is a common calculation error.

Question 23Radio Frequency Fundamentals and Spectrum Concepts

Which statement about the relationship between frequency, period, and wavelength is correct?

  1. Period is inversely proportional to frequency and wavelength is proportional to frequency
  2. Period is proportional to frequency and wavelength is inversely proportional to frequency
  3. Period is inversely proportional to frequency and wavelength is inversely proportional to frequency Correct answer.
  4. Period is proportional to frequency and wavelength is proportional to frequency

Explanation

Period equals 1/f, so it falls as frequency rises, and wavelength equals c/f, so it also falls as frequency rises. Both quantities are therefore inversely proportional to frequency. Keeping these two relationships straight avoids unit and scaling errors in link design.

Question 24Radio Frequency Fundamentals and Spectrum Concepts

An engineer doubles both the transmitter power and the antenna gain while the receiver and distance stay the same. What is the approximate net change in received power in dB?

  1. 20 dB
  2. 6 dB Correct answer.
  3. 3 dB
  4. 10 dB

Explanation

Doubling power contributes about 3 dB and doubling antenna gain contributes another 3 dB, for roughly 6 dB total. When quantities in decibels are cascaded, their dB values add rather than multiply. This additive property is why decibels simplify link budgets.

Question 25Radio Frequency Fundamentals and Spectrum Concepts

A receiver must detect a signal at -110 dBm in a 200 kHz channel. Which change would most improve the achievable signal-to-noise ratio without altering the transmitted power?

  1. Increasing the receiver bandwidth
  2. Reducing the receiver noise figure Correct answer.
  3. Increasing the antenna feedline loss
  4. Lowering the antenna gain

Explanation

Reducing the noise figure lowers the noise floor, which directly improves the signal-to-noise ratio for a given signal level. Wider bandwidth admits more noise, and added feedline loss or reduced gain lowers the received signal. Noise figure is therefore the key receiver parameter to optimize.

Question 26Radio Frequency Fundamentals and Spectrum Concepts

An antenna is described as having 6 dBi of gain. What does the "i" in dBi indicate about the reference used?

  1. The gain is referenced to a short vertical whip over a ground plane
  2. The gain is referenced to an isotropic radiator that radiates equally in all directions Correct answer.
  3. The gain is referenced to a half-wave dipole in free space
  4. The gain is referenced to the transmitter output measured in milliwatts

Explanation

The suffix "i" in dBi means the gain is expressed relative to an isotropic radiator, a theoretical antenna that radiates uniformly in every direction with 100 percent efficiency. Because the isotropic radiator is the fundamental reference, dBi values are always 2.15 dB higher than the same antenna expressed in dBd.

Question 27Radio Frequency Fundamentals and Spectrum Concepts

A regulator wants to describe how much of the radio spectrum is occupied by a single digital emission so that adjacent channels can be planned without interference. Which emission characteristic should be specified?

  1. The spurious emission limit measured at the antenna port
  2. The frequency tolerance allowed for the transmitter's carrier under all conditions
  3. The peak envelope power measured during the strongest modulation excursion
  4. The occupied bandwidth containing a defined percentage of the emission's total mean power Correct answer.

Explanation

Occupied bandwidth defines the width of the frequency range that contains a specified percentage (commonly 99 percent) of an emission's mean power, which is exactly what channel planning needs to avoid overlap. Peak envelope power, frequency tolerance, and spurious limits describe other aspects of transmitter performance and do not quantify spectral width.

Question 28Radio Frequency Fundamentals and Spectrum Concepts

A transmitter feeds 40 W into a coaxial cable that has 3 dB of loss. What power reaches the antenna?

  1. 20 W Correct answer.
  2. 80 W
  3. 10 W
  4. 37 W

Explanation

A loss of 3 dB corresponds to halving the power, so 40 W is reduced to 20 W at the antenna. Losses in decibels add along the chain, and each 3 dB of attenuation removes half of the remaining power.

Question 29Radio Frequency Fundamentals and Spectrum Concepts

A station transmits at 145 MHz while a nearby receiver is tuned to 435 MHz. Which relationship between these two signals is being described?

  1. They are co-channel signals because both propagate by line of sight
  2. They are harmonically related because 435 MHz is an exact multiple of 145 MHz
  3. They lie in different bands, with the second frequency roughly three times the first Correct answer.
  4. They occupy the same band because both fall within the VHF range

Explanation

145 MHz lies in the 2 m VHF band while 435 MHz lies in the 70 cm UHF band, so they are separated by band as well as by roughly a factor of three in frequency. Band membership is determined by the ITU frequency ranges, not by propagation mode.

Question 30Radio Frequency Fundamentals and Spectrum Concepts

An HF circuit is planned between two points 2,000 km apart. The operator observes that contacts are possible on 14 MHz during daylight but the same path fails on 28 MHz at midday, while 28 MHz works well near sunset. Which explanation best fits these observations?

  1. The maximum usable frequency for the path is lower at midday than in the evening, so 28 MHz is above the daytime MUF Correct answer.
  2. The maximum usable frequency falls as the ionosphere darkens, so 28 MHz is supported only when the MUF drops below 14 MHz
  3. The lower frequency is absorbed more strongly in daylight, so only 28 MHz can use the daytime path
  4. The higher frequency needs a lower critical frequency, so it is only supported when the ionosphere weakens after sunset

Explanation

The maximum usable frequency for an ionospheric path depends on the ionization density along the path; stronger daytime ionization generally raises the MUF, but for a given 2,000 km path the effective MUF at midday can still be below 28 MHz while 14 MHz remains usable. As the ionosphere weakens toward evening the MUF drops, and the observation that 28 MHz works near sunset is consistent with the path geometry and MUF changing rather than with a simple rule that higher frequencies need lower critical frequencies.

Question 31Public Safety Land Mobile Radio Systems and Architectures

In a public safety land mobile radio system, what does the term 'talkgroup' primarily define?

  1. A frequency pair assigned to a single subscriber unit for its exclusive use
  2. A cryptographic key set used to encrypt transmissions between two radios
  3. A physical repeater site that provides coverage to a single county
  4. A logical grouping of radios that share a common voice channel selection and hear each other's calls Correct answer.

Explanation

A talkgroup is a logical identity that lets a defined set of subscribers share calls on a trunked or conventional system, regardless of which site or channel each radio is currently using. It is an addressing concept, not a physical site, a dedicated frequency, or an encryption artifact.

Question 32Public Safety Land Mobile Radio Systems and Architectures

Which trunking behavior most directly improves channel efficiency compared with a conventional repeater system?

  1. All subscribers transmit continuously so the controller can track them
  2. Channels are pooled and assigned on demand from a controller rather than fixed to a user group Correct answer.
  3. Voice is always digitized at the lowest possible bit rate to save bandwidth
  4. Each talkgroup is permanently assigned its own dedicated repeater channel

Explanation

Trunking pools a limited number of channels and grants them on demand, so a small number of channels can serve many talkgroups with low blocking probability. Fixed per-group channel assignment is the conventional model that trunking is designed to replace.

Question 33Public Safety Land Mobile Radio Systems and Architectures

A dispatcher needs to reach every radio affiliated to a talkgroup across all sites in a wide-area system with a single transmission. Which call type is designed for this?

  1. A data call to the console's registration server
  2. A group call to the talkgroup, delivered to all affiliated sites Correct answer.
  3. A private call to one subscriber unit
  4. An emergency call to a single site controller

Explanation

A group call addressed to a talkgroup is routed to every site where at least one subscriber is affiliated, giving system-wide reach in one transmission. Private calls target one unit, and the other options do not distribute voice to the group.

Question 34Public Safety Land Mobile Radio Systems and Architectures

What is the primary purpose of a site affiliation in a multi-site trunked radio system?

  1. To tell the system which site should deliver group calls to a given subscriber Correct answer.
  2. To authenticate the subscriber's encryption keys at power-up
  3. To record the subscriber's GPS position for mapping only
  4. To assign the subscriber a permanent home channel for all transmissions

Explanation

Affiliation registers a subscriber at a site so the system knows where to route group traffic for that radio. Without affiliation, the system cannot efficiently deliver calls to the correct site.

Question 35Public Safety Land Mobile Radio Systems and Architectures

In a conventional (non-trunked) repeater system, what typically determines whether a subscriber hears a transmission?

  1. Whether the radio has an active registration with the network core
  2. Whether the subscriber is affiliated to the correct wide-area site
  3. Whether the controller grants the subscriber a pooled channel
  4. Whether the radio is tuned to the same channel and tone/color code as the transmitting unit Correct answer.

Explanation

Conventional systems use a fixed channel plus a subaudible or digital squelch code (such as CTCSS or a color code) to select which transmissions a radio will unmute. Channel pooling, affiliation, and core registration are trunking concepts.

Question 36Public Safety Land Mobile Radio Systems and Architectures

Which frequency band is most commonly associated with legacy VHF public safety land mobile radio in North America?

  1. 806-824 MHz
  2. 450-470 MHz
  3. 150-174 MHz Correct answer.
  4. 1850-1910 MHz

Explanation

The 150-174 MHz range is the classic VHF high-band allocation used for public safety land mobile radio. The 450-470 MHz range is UHF, 806-824 MHz is the 800 MHz band, and 1850-1910 MHz is PCS, not land mobile public safety.

Question 37Public Safety Land Mobile Radio Systems and Architectures

What does P25 Phase 2 improve relative to Phase 1 in a trunked system?

  1. It uses a wider 25 kHz channel to increase audio fidelity
  2. It uses two-slot TDMA on a 12.5 kHz channel to double voice capacity per channel Correct answer.
  3. It eliminates the need for a system controller
  4. It replaces digital voice with analog FM for backward compatibility

Explanation

P25 Phase 2 employs two-slot TDMA within a 12.5 kHz channel, effectively providing two voice paths per channel and doubling capacity compared with Phase 1's FDMA approach. It does not widen channels or revert to analog.

Question 38Public Safety Land Mobile Radio Systems and Architectures

What is the function of a control channel in a trunked radio system?

  1. It carries only encrypted data between consoles
  2. It carries all voice traffic for the system
  3. It provides backup power to repeater sites
  4. It carries signaling that grants voice channels and manages subscriber requests Correct answer.

Explanation

The control channel carries outbound and inbound signaling so the controller can grant channels, track affiliations, and manage calls. Voice traffic is carried on separate traffic channels once a grant is issued.

Question 39Public Safety Land Mobile Radio Systems and Architectures

A radio is affiliated to a talkgroup but its user reports hearing no traffic while other units on the same talkgroup do. Which troubleshooting step is most appropriate first?

  1. Re-key the encryption on all radios in the fleet
  2. Verify the radio's selected talkgroup and site affiliation match the active group Correct answer.
  3. Replace the antenna on the affected radio
  4. Reboot the system controller

Explanation

If other units receive the traffic, the network is delivering the call, so the issue is likely local selection or affiliation. Confirming the talkgroup and site affiliation is a low-risk first step before hardware or system-wide actions.

Question 40Public Safety Land Mobile Radio Systems and Architectures

A talkgroup is delivered to a site only when at least one subscriber is affiliated there. What is this behavior called?

  1. Roaming handoff
  2. Priority scan
  3. Affiliation-based (on-demand) site routing Correct answer.
  4. Simulcast transmission

Explanation

On-demand routing delivers group traffic only to sites with affiliated subscribers, conserving backhaul and channel resources. Simulcast, roaming, and scan are different mechanisms that do not describe this resource-saving routing.

Question 41Public Safety Land Mobile Radio Systems and Architectures

Why is simulcast used in wide-area public safety radio systems?

  1. To route private calls through a single repeater
  2. To transmit the same signal on the same frequency from multiple sites to reduce coverage gaps and handoff disruptions Correct answer.
  3. To assign different frequencies to each site for maximum channel reuse
  4. To encrypt traffic differently at each site

Explanation

Simulcast broadcasts the same signal on the same frequency from synchronized sites, filling coverage gaps and avoiding hard handoffs at site boundaries. It requires careful timing to avoid interference in overlap zones.

Question 42Public Safety Land Mobile Radio Systems and Architectures

What is the primary risk in a simulcast overlap region if site timing is not properly synchronized?

  1. Subscribers are forced to affiliate to a different talkgroup
  2. The control channel automatically changes frequency
  3. Encryption keys are automatically rotated
  4. Destructive interference that degrades or drops received audio Correct answer.

Explanation

In simulcast overlap zones, signals arriving with different delays can combine destructively, producing distortion or dropped audio. Precise timing alignment and delay equalization are required to keep the overlap usable.

Question 43Public Safety Land Mobile Radio Systems and Architectures

A subscriber traveling between sites in a multi-site trunked system needs to keep receiving its talkgroup. What mechanism supports this?

  1. The radio re-affiliates at the new site and the system routes group traffic there Correct answer.
  2. The radio permanently locks to its original site
  3. The radio disables its encryption during travel
  4. The radio switches to a conventional channel automatically

Explanation

As the subscriber moves, it registers or affiliates at the new site, and the system updates routing so group calls follow the radio. This is the basis of seamless wide-area roaming.

Question 44Public Safety Land Mobile Radio Systems and Architectures

Which statement best describes the role of a comparator in a voted receive system?

  1. It assigns voice channels to requesting talkgroups
  2. It synchronizes simulcast transmitters
  3. It selects the best-quality audio from multiple receivers covering the same channel Correct answer.
  4. It encrypts outbound control channel data

Explanation

A comparator (voter) evaluates audio from several receivers on the same channel and passes the best signal to the console, improving inbound coverage. Channel assignment, encryption, and simulcast timing are separate functions.

Question 45Public Safety Land Mobile Radio Systems and Architectures

What is the main purpose of a backup control channel in a trunked system?

  1. To carry voice traffic when all traffic channels are busy
  2. To maintain system signaling if the primary control channel fails Correct answer.
  3. To synchronize GPS clocks at sites
  4. To provide encryption key distribution

Explanation

A backup control channel provides redundancy so subscribers can continue to register and receive grants if the primary control channel is lost. It is a signaling path, not a voice or key-management resource.

Question 46Public Safety Land Mobile Radio Systems and Architectures

A P25 system uses a talkgroup with encryption enabled, but one subscriber hears only garbled audio. What is the most likely cause?

  1. The control channel is on a backup frequency
  2. The subscriber lacks the correct encryption key for that talkgroup Correct answer.
  3. The subscriber is scanning too many channels
  4. The subscriber's antenna is too short for the band

Explanation

Garbled audio on an encrypted talkgroup typically indicates a key mismatch, such as a missing or incorrect key in that radio. Physical or system-level issues would usually affect reception or access rather than producing decryptable-but-wrong audio.

Question 47Public Safety Land Mobile Radio Systems and Architectures

Which architecture places the channel controller and core functions at a central location with sites connected by backhaul?

  1. A direct-mode simplex network
  2. A single-site conventional repeater
  3. A centralized (star) trunked architecture Correct answer.
  4. A standalone repeater with no controller

Explanation

A centralized architecture keeps the controller and core at a central point, with remote sites linked by backhaul for signaling and voice. Single-site, simplex, and controller-less repeaters lack this centralized multi-site structure.

Question 48Public Safety Land Mobile Radio Systems and Architectures

In a distributed core architecture, what is a key advantage over a single centralized core?

  1. Improved resilience because call control can continue if one core node fails Correct answer.
  2. Elimination of the need for site backhaul
  3. Guaranteed unlimited voice capacity per site
  4. Removal of the requirement for subscriber affiliation

Explanation

Distributing core functions across nodes provides redundancy so that failure of one node does not necessarily stop call processing. Backhaul, capacity limits, and affiliation requirements still apply.

Question 49Public Safety Land Mobile Radio Systems and Architectures

A first responder presses the emergency button on a P25 subscriber. Which behavior best characterizes a properly configured emergency alarm?

  1. The radio disables its encryption automatically
  2. The radio shuts down to preserve battery
  3. The radio switches to a conventional simplex channel
  4. A high-priority indication is sent to the console and the radio is granted priority access to the system Correct answer.

Explanation

An emergency alarm alerts the dispatcher and typically grants the subscriber priority access so its traffic is handled ahead of routine calls. It does not change channel type, disable encryption, or power down the radio.

Question 50Public Safety Land Mobile Radio Systems and Architectures

What does a site's 'busy' or blocking probability describe in trunked capacity planning?

  1. The number of subscribers affiliated to the site
  2. The average battery life of subscriber radios
  3. The likelihood that a call request is denied because no traffic channel is available Correct answer.
  4. The percentage of time the control channel is idle

Explanation

Blocking probability estimates how often a request finds all channels occupied and is queued or denied. It is a function of offered load and channel count, not of control channel idle time, affiliation count alone, or battery life.