Section 114 Communications

Question 1

What is amplitude

Answer 1

More energy a wave is carrying the more amplitude it has

Question 2

What is wavelength

Answer 2

Distance of a complete wave cycle (usually peak-peak or trough-trough)

Question 3

What is Frequency

Answer 3

• Number of wave cycles per unit of time
• Hz = Waves/sec
• Higher frequency transmits more info faster

Question 4

What is the HF Frequency Band

Answer 4

HF = 1.600-29.999 MHz

Question 5

What is the VHF frequency band

Answer 5

VHF = 30.000-224.999 MHz

Question 6

What is the UHF frequency band

Answer 6

225.000-3,000 MHz (3GHz)

Question 7

What are the UHF propagation characteristics and what is it used for?

Answer 7

• Line of sight propagation
• Forward Air Control (FAC)
• LOS Comms

Question 8

What are HF propagation characteristics, range and uses?

Answer 8

• Long and short range secure voice and data comms
• Range: 30km man pack / 100km vehicle
• Ground wave and Sky wave propagation (over the horizon)
• Sky wave: ionosphere bounce w/ skip zone
• Ground wave: decreased range with vegetation, mountains, dry desert

Question 9

What is a net and what is net control

Answer 9

Net: a frequency and all stations using it.

Net Control: station responsible for managing traffic on that net

Question 10

What are the Transmission Power Levels & Ranges?

Answer 10

• LO (manpack/vehicular lo) 200-400m
• M (medium) 400m-5km
• Hi (high) 5-10km
• PA (power amplified) 10-40km

Question 11

What is critical LOS or optical LOS

Answer 11

Two antennas need to be able to “see” each other to function. Applies to UHF. Waves reflect which may benefit in MOUT

Question 12

What are the data transmission speeds for UHF and HF

Answer 12

UHF: up to 16kbps
HF: up to 2.4kbps

Question 13

What are vulnerabilities of UHF

Answer 13

• Absorbed by foliage (decreased range)
• Vulnerable to radio direction finding (RDF)
• Usually poor performance in rural areas

Question 14

What is the primary MAGTF VHF Radio

Answer 14

• Single Channel Ground and Airborne Radio System (SINCGARS)

- Uses frequency hopping, integrated COMSEC

Question 15

VHF Characteristics and Planning Factors

Answer 15

• “radio LOS” instead of optical or critical
• Diffracts around curvature of the earth but much less than HF
• Absorbed by foliage but less than UHF
• Good performance in rural areas
• vulnerable to accurate RDF

Question 16

HF Characteristics and Planning Factors

Answer 16

• Capable of long & short range secure voice and data comms
• Data comms are very slow: 2.4kbps
• Modem must be designed for ops in this band

Question 17

What are the 3 types of HF Sky waves

Answer 17

• Near Vertical Incidence Skywave (NVIS) near 90 degree
• Medium-Haul skywave approx 50 degree
• Long-Haul skywave approx 20 degree

Question 18

HF disadvantages/limitations

Answer 18

• Slow data rate
• can be intercepted/traced by enemies 100s of miles away
• limited bandwidth
• solar storms can eliminate HF

Question 19

What bands do single channel radios (SCR) work in?

Answer 19

• HF
• VHF
• UHF
• UHF-tactical satellite (TACSAT)

Question 20

What are the benefits of frequency hopping

Answer 20

• Prevents enemy from jamming or locking on to a freq

Question 21

What is the channel spacing and timing for frequency hopping?

Answer 21

• 25 KHz channel spacing

- all radios must be synch’d within 4 seconds

Question 22

What is a Hopset?

Answer 22

The set of frequencies on which an FH net hops

Question 23

What is the difference between plain text and cipher text?

Answer 23

• Plain text: uncovered

- Cypher text: covered/encrypted