Mod 9-10-11-12 Flashcards
What is the range of operating frequencies for VHF com systems on an aircraft?
118.000 MHz to 135.975 MHz
What is the purpose of the ‘test’ switch on a VHF com control panel?
To disable the squelch circuit, allowing the background noise to be heard
When adjusting the squelch control on a VHF com system, why is it important to NOT turn the squelch too far past the point where the noise disappears?
It may cause a weak station to not be received
Which of the following radio circuits is NOT part of the receiver function of an aircraft VHF com radio?
Compression circuit
Which of the following specifications for receiver sensitivity would provide the greatest range (distance between transmitter and receiver), while still allowing a signal to be heard?
2 µV, for 6 dB S/N ratio
Which type of antenna is used with an aircraft VHF com system?
A ¼ wavelength vertically polarized antenna
How much of an increase in transmitter output power would be required in order to double the range?
4 times the power
What is the effective range of a VHF com transceiver on an aircraft that is flying at 4500 feet above ground level (AGL)?
73.8
What is the range of operating frequencies for aircraft HF?
2.0 MHz to 30 MHz
Which of the following components is used in an aircraft HF system but not in an aircraft VHF com system?
antenna coupler
Which control in an HF system is used to fine-tune the frequency of the received audio signal?
Amplitude Modulation (AM) and Single Side Band (SSB)
Which method of propagation is primarily utilized by an aircraft HF system?
sky wave
Which antenna location identified by the lettering on the photo above is the HF antenna?
D
When an HF system is first keyed after tuning to a new frequency, a tone is heard on the headset for approximately 10 seconds. What does the presence of the tone indicate?
That the antenna coupler is matching the antenna to the selected frequency
Aircraft HF communications systems are used for long-range communications in remote areas and for trans-oceanic operations.
yes
The reliability of HF communications is highly dependent on the conditions presented by the troposphere.
no
Which of the following best describes the purpose of a SELCAL system on an aircraft?
It allows the crew to be alerted when they are being called
What best describes the modulation format for a SELCAL encoded call?
Consists of two pairs of two audio tones amplitude modulated on the RF
What system is used for identifying a specific aircraft for SELCAL?
One that uses a four-letter code assigned to the aircraft
What is the time between the pairs of tones in a SELCAL transmission?
0.2 seconds
How is the SELCAL code selected for a specific aircraft?
It’s set with rotary switches or jumpers in the aircraft
Which of the following is a valid SELCAL code for an aircraft?
FLAP
The tones used for encoding SELCAL fall within the range of sounds that humans can hear. (1 mark each)
yes
SELCAL cannot be used with an HF communications system on an aircraft.
true or false
false
