Module 3-4 Flashcards
What is the frequency range for VHF comms?
118.00 - 135.975 MHz
What frequencies define the VHF spectrum?
30Mhz - 300MHz
What is the purpose of a mic key line?
It allows the transceiver to turn from a reciever, to a transmitter, essentially enabling a PTT function.
There are 2 frequencies on the Comm radio. The top is the ________ and the bottom is the _______ frequency
Active
Standby
What is the purpose of a receiver squelch circuit?
The squelch mutes or silences the output of the frequency when you are transmitting to eliminate audio feedback
What does the “com test” control provide?
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.
Why is HF not as reliable as VHF?
HF is prone to atmospheric noise, where at VHF is prone to very little atmospheric noise
What does an antenna coupler do?
It electronically alters the antenna to be longer or shorter through inductance and capacitance to switch from HF to VHF
Where is the HF typically mounted on airliners?
The vertical stabilizer
What does SELCAL stand for?
Selective calling
Give 2 reasons why SELCAL is used
It allows airliners to call specific aircraft
It reduces the pilots workload
What 3 frequencies are distress calls sent out on by an ELT?
- 500 MHz
- 00 MHz
- 00 MHz
A radiowave travels at the rate of
3 x 10^8 meters per second
Aircraft comms between 108.00 MHz - 135.975 MHz are considered what type of frequency?
VHF
What is the name of the HF signal that bounces off the ionosphere and back to the earth?
Sky wave propagation
What is the type of HF signal that travels along the curvature of the earth?
ground wave propagation
What is the type of HF signal that does not bounce back to earth?
Space wave propagation
3000kHz is how many MHz?
3.0MHz
Waves usually below the MF band travel as ________ waves
ground waves
Why should antennas never be re painted?
There is a special process for painting for the antenna to work properly
What does “omnidirectional” mean?
This means it radiates in all directions except directly above or directly below it (Vertically polarized)
3 components of a basic transmission system
Transmitter
Path (The frequency traveling through the air)
Receiver
A VHF comm radio is a half duplex system which means
The signals may be transmitted in both directions but not at the same time
How do you determine the wavelength of an antenna? How do you determine the actual length of the antenna?
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
How to measure the impedance of a headset?
Put one lead on the BARREL
Put one lead on the TIP
The normal _______ ___________ for an aircraft transceiver is 1 minute transmit by 4 minute of rest
Duty cycle
