CED Radio & Telecommunication Systems 3 — Questions and Answers
Question 1: A dispatcher hears two units transmitting at the same time, causing an unintelligible noise. This is called:
- Simulcasting
- Doubling or kerchunking (Correct answer)
- Squelch break
- Interference patching
Correct answer: Doubling or kerchunking
When two units transmit simultaneously on the same frequency, the overlapping signals create noise called 'doubling,' making neither transmission intelligible.
Question 2: What is the function of the squelch control on a radio?
- To increase transmission power during low-signal conditions
- To suppress background noise when no signal is being received (Correct answer)
- To encrypt outgoing transmissions
- To switch between primary and secondary channels
Correct answer: To suppress background noise when no signal is being received
Squelch mutes the receiver's audio output when signal strength falls below a set threshold, eliminating static noise between transmissions.
Question 3: During a major incident, the Incident Commander requests a dedicated radio channel for command communications. The dispatcher should:
- Assign an existing talk group or channel per agency protocol and notify all affected units (Correct answer)
- Deny the request unless approved by a supervisor
- Open all channels to allow unrestricted communication
- Patch the IC into the public telephone system
Correct answer: Assign an existing talk group or channel per agency protocol and notify all affected units
Dispatchers should follow agency protocol to assign a dedicated channel or talk group and notify all units of the change to maintain organized command communications.
Question 4: What is the primary advantage of P25 (Project 25) digital radio standards in public safety?
- Lower cost compared to all analog systems
- Standardized interoperability between different manufacturers' equipment (Correct answer)
- Unlimited range without repeaters
- Automatic encryption of all transmissions by default
Correct answer: Standardized interoperability between different manufacturers' equipment
P25 establishes common technical standards so that public safety radios from different manufacturers can communicate with each other.
Question 5: A unit transmits 'Signal 9' and then goes silent. If 'Signal 9' means officer needs assistance, the dispatcher should FIRST:
- Log the transmission and wait 30 seconds for a follow-up
- Immediately broadcast on the channel for the unit to confirm their status and location (Correct answer)
- Call the unit's supervisor to verify
- Switch to the backup channel and wait
Correct answer: Immediately broadcast on the channel for the unit to confirm their status and location
When a distress signal is received, the dispatcher must immediately broadcast to confirm unit status and location to initiate appropriate response.
Question 6: In radio communications, what does 'radio dead zone' or 'shadow' refer to?
- A scheduled maintenance window when radios are offline
- A geographic area where radio signals cannot reliably reach due to terrain or structures (Correct answer)
- A channel reserved for encrypted emergency traffic only
- The delay between a dispatcher's transmission and a unit's receipt
Correct answer: A geographic area where radio signals cannot reliably reach due to terrain or structures
A dead zone is an area where terrain features, buildings, or other obstacles block or absorb radio signals, preventing reliable coverage.
Question 7: What does 'DTMF' stand for in the context of telephone and radio systems?
- Digital Trunk Management Framework
- Dual-Tone Multi-Frequency (Correct answer)
- Direct Transmission Mode Function
- Dispatcher Telephone Monitoring Feed
Correct answer: Dual-Tone Multi-Frequency
DTMF (Dual-Tone Multi-Frequency) is the signaling system used by telephone keypads that generates a combination of two audio tones for each digit.
CED Radio & Telecommunication Systems 3
A dispatcher hears two units transmitting at the same time, causing an unintelligible noise.
This is called: