FMF Combat Communications 3 — Questions and Answers
Question 1: What frequency range is typically associated with VHF (Very High Frequency) communications?
- 3–30 MHz
- 30–300 MHz (Correct answer)
- 300–3000 MHz
- 3–30 GHz
Correct answer: 30–300 MHz
VHF communications operate in the 30–300 MHz range, and are commonly used for short-range tactical communications in the Marine Corps.
Question 2: Which of the following best describes 'frequency hopping' in secure radio communications?
- Manually changing frequencies every hour based on a schedule
- Rapidly switching transmission frequencies in a pre-determined pseudo-random sequence to prevent jamming and interception (Correct answer)
- Using two frequencies simultaneously to increase bandwidth
- Alternating between AM and FM modes to confuse enemy listeners
Correct answer: Rapidly switching transmission frequencies in a pre-determined pseudo-random sequence to prevent jamming and interception
Frequency hopping spreads transmissions across many frequencies in a synchronized pseudo-random pattern, making it extremely difficult for adversaries to intercept or jam.
Question 3: What does the proword 'BREAK' indicate when used in voice communications?
- The transmission is being interrupted by a higher-priority message
- A separation between portions of the message, especially between the address and the text (Correct answer)
- The communicator has finished transmitting and is closing the net
- Authentication has failed and the message should be disregarded
Correct answer: A separation between portions of the message, especially between the address and the text
'BREAK' is used to indicate a separation between portions of a message, most commonly between the address group and the text, to improve clarity.
Question 4: In what situation would a Marine use a 'relay station' for communications?
- When communicating with a unit on the same hilltop
- When terrain or distance prevents two stations from communicating directly (Correct answer)
- When transmitting encrypted data over satellite
- When the NCS is unavailable and a backup must authenticate traffic
Correct answer: When terrain or distance prevents two stations from communicating directly
A relay station is used when terrain masking or excessive distance prevents two stations from achieving direct radio contact, allowing a third station to pass traffic between them.
Question 5: What is the correct format for a standard military grid reference used in communication messages?
- Latitude and longitude in decimal degrees
- A six-, eight-, or ten-digit grid reference based on the Military Grid Reference System (MGRS) (Correct answer)
- An alphanumeric code assigned by the operations center
- GPS coordinates expressed in degrees, minutes, and seconds
Correct answer: A six-, eight-, or ten-digit grid reference based on the Military Grid Reference System (MGRS)
MGRS grid references provide a standardized, concise way to communicate locations on military maps using six, eight, or ten digits for varying levels of precision.
Question 6: What action should a radio operator take if they suspect an enemy is attempting to 'spoof' their net?
- Immediately switch to satellite communications
- Challenge the unknown station using authentication procedures (Correct answer)
- Cease all communications until higher headquarters grants clearance
- Increase transmitter power to override the spoofed signal
Correct answer: Challenge the unknown station using authentication procedures
Authentication challenges verify that a station is friendly by requiring a correct response known only to authorized net members, countering spoofing attempts.
Question 7: Which type of wire line provides the most secure means of battlefield communication?
- Unsecured field telephone wire (TA-1/PT)
- Single wire ground return
- Secure voice over fiber-optic cable (Correct answer)
- AM broadcast over commercial frequencies
Correct answer: Secure voice over fiber-optic cable
Fiber-optic cable does not emit electromagnetic radiation and is extremely difficult to tap, making it the most secure wire-line communication method in a battlefield environment.
FMF Combat Communications 3
What frequency range is typically associated with VHF (Very High Frequency) communications?