Module 3-4

Question 1

What is the frequency range for VHF comms?

Answer 1

118.00 - 135.975 MHz

Question 2

What frequencies define the VHF spectrum?

Answer 2

30Mhz - 300MHz

Question 3

What is the purpose of a mic key line?

Answer 3

It allows the transceiver to turn from a reciever, to a transmitter, essentially enabling a PTT function.

Question 4

There are 2 frequencies on the Comm radio. The top is the ________ and the bottom is the _______ frequency

Answer 4

Active

Standby

Question 5

What is the purpose of a receiver squelch circuit?

Answer 5

The squelch mutes or silences the output of the frequency when you are transmitting to eliminate audio feedback

Question 6

What does the “com test” control provide?

Answer 6

It turns the squelch off, allowing atmospheric or static noise to come through the receiver, allowing for comfortable volume control. This verifies whether or not the transceiver is actually working.

Question 7

Why is HF not as reliable as VHF?

Answer 7

HF is prone to atmospheric noise, where at VHF is prone to very little atmospheric noise

Question 8

What does an antenna coupler do?

Answer 8

It electronically alters the antenna to be longer or shorter through inductance and capacitance to switch from HF to VHF

Question 9

Where is the HF typically mounted on airliners?

Answer 9

The vertical stabilizer

Question 10

What does SELCAL stand for?

Answer 10

Selective calling

Question 11

Give 2 reasons why SELCAL is used

Answer 11

It allows airliners to call specific aircraft

It reduces the pilots workload

Question 12

What 3 frequencies are distress calls sent out on by an ELT?

Answer 12

121. 500 MHz
122. 00 MHz
123. 00 MHz

Question 13

A radiowave travels at the rate of

Answer 13

3 x 10^8 meters per second

Question 14

Aircraft comms between 108.00 MHz - 135.975 MHz are considered what type of frequency?

Answer 14

VHF

Question 15

What is the name of the HF signal that bounces off the ionosphere and back to the earth?

Answer 15

Sky wave propagation

Question 16

What is the type of HF signal that travels along the curvature of the earth?

Answer 16

ground wave propagation

Question 17

What is the type of HF signal that does not bounce back to earth?

Answer 17

Space wave propagation

Question 18

3000kHz is how many MHz?

Answer 18

3.0MHz

Question 19

Waves usually below the MF band travel as ________ waves

Answer 19

ground waves

Question 20

Why should antennas never be re painted?

Answer 20

There is a special process for painting for the antenna to work properly

Question 21

What does “omnidirectional” mean?

Answer 21

This means it radiates in all directions except directly above or directly below it (Vertically polarized)

Question 22

3 components of a basic transmission system

Answer 22

Transmitter
Path (The frequency traveling through the air)
Receiver

Question 23

A VHF comm radio is a half duplex system which means

Answer 23

The signals may be transmitted in both directions but not at the same time

Question 24

How do you determine the wavelength of an antenna? How do you determine the actual length of the antenna?

Answer 24

Velocity / Frequency = Wavelength
3 x 10^8 / 135.975 = 2.206 meters
The length is usually either 1/2 wavelength long or a 1/4 wavelength long

Question 25

How to measure the impedance of a headset?

Answer 25

Put one lead on the BARREL

Put one lead on the TIP

Question 26

The normal _______ ___________ for an aircraft transceiver is 1 minute transmit by 4 minute of rest

Answer 26

Duty cycle