elective hf

3MHZ TO 30 MHZ

HF FREQUENCY RANGE

TRUE

VHF communication is primarily limited by line-of-sight propagation. HF, on the other hand, can use the ionized layers of the upper atmosphere to propagate radio waves over much longer distances.

SO HF FOR LONG DISTANCE

2.85 MHZ TO 23.35 MHZ

ALLOTED HF BANDS

VHF

uses conventional AM (with a carrier and two sidebands) primarily because of aviation's established communication standards and operational requirements,

bandwidth and transmitter power

hf commonly uses SSB to conserve _______ __ ______ ____ for long - distance communication

2 maximum audio frequency

bandwidth dsb

1 maximum audio frequency

bandwidth ssb

complicated

receiver ssb. carrier must be recreated

no

is dsb power efficient?

yes

is ssb power efficient?

selcal

helps ensure that crews do not need to continuously monitor noisy HF channels.

selcal codes

are uniquely allocated to particular aircraft by air traffic control

short burst

selcal operates by transmitting a ____ of audio tones.

tone pulses

Each SELCAL code consists of two consecutive ___

1 second duration 0.2 second interval

duration of tone pulses and interval

312.6

selcal tone A

vdl

used heavily during continental operation

HFDL

useful for oceanic or polar operation

phase shift keying

modulation technique of vhf

phase shift keying

binary signal to be transmitted changes the phase shift of a sine wave character depending upon whether a binary 0 or binary 1 is to be transmitted

24 BIT

Every aircraft has its own identifier which is a ___ ICAO Address.

8 bit

once aircraft is logged on, the aircraft is allocated an ___ address code

32

Each ground station transmits a “squitter” frame every __ seconds.

balance modulator

in transmit mode The DSB suppressed - carrier signal is generated using a ?

in transmit mode The balanced modulator removes the carrier, leaving only the upper and lower sidebands.

squitter

avoids data collision and ensures reliable communication

vertical stabilizer

Early aircraft commonly used external wire antennas, typically running from the fuselage to the top of the ?.

external

However, ___ wire antennas proved unreliable and unsuitable for modern high -speed passenger aircraft.

probe

Large external ___ antennas are also undesirable due to their vulnerability to static discharge and lightning strikes.

tailfin mounted antenna

is an effective location for an internal HF antenna.

notch antenna

uses part of the aircraft structure/airframe as part of the radiating system.

standing wave ratio

indicates how well a load is impedance -matched to a transmission line.

hf coupler

matches the HF antenna to the radio across the operating frequency range.

single side band

What sideband is used for aircraft HF communication?

sellective calling

What does SELCAL do? -automatic alert that tells the crew, “Someone is calling your aircraft.”

Phase Shift Keying - 300,600,1200, and 1800 bps

What modulation does HFDL use and what data rates are usually used?

true

What is the purpose of the HF antenna coupling unit? match the radio to the antenna