Midterm 1 Flashcards
Why are High Frequency communications not as reliable as those of VHF?
High Frequency radio travels by “skipping” through the ionosphere, an electrical mirror that reflects radio waves back to earth. Communications are constantly interrupted due to the change of the ionosphere between day and night, season to season, and magnetic storms. Interruptions can last for hours or days.
What is the advantage of “Autotune”?
Autotune is a tuning unit that matches a short, fixed antenna on the airplane to the wavelength of any HF frequency. The advantage of this unit is that it is done automatically when the pilot selects a channel.
Why is SSB (single sideband) more efficient than conventional AM radio?
An AM transmitter generates three components of a radio-frequency (RF) carrier, an upper sideband, and a lower sideband. Since the audio (or voice) is only found in the sidebands, sidebands can travel with or without the carrier, more than two-thirds of the transmitter power is lost in the carrier, in addition to the sidebands ability to travel better through worsening ionospheric conditions, it was more practical and efficient for the electronic industry to develop stable transmitters and receivers for the sidebands. It is called SSB because both upper and lower sidebands carry identical information.
What made HF datalink successful?
Some of the successful attributes of datalink are: Lower pilot workload, shorter message transmission time, less operational training for flight crew, it is less prone to human error interpretations, and it automatically retransmits if the data detects any errors.
What are the three major components of an HF line-replacement unit (LRU)?
Antenna coupler, power amplifier, & receiver-exciter
Name two advantages of HF datalink?
Data relieves congestion on voice frequencies, & Data is able to extract signals better in noisier environments.
What is the purpose of an HF antenna coupler?
The coupler matches any HF frequency (2-30 MHz) and sends it through a feedline to the antenna.
Where is the HF antenna mounted on many airliners?
Located in the vertical tail fin.
What frequencies define the Very High Frequency (VHF) band?
118.00 to 136.975 MHz
What is the frequency coverage of the VHF com band?
over 2,280 channels when spacing is at 8.33 kHz.
What is splitting channels?
“Splitting” channels means dividing the space occupied by one frequency allowing channels to move closer together within the same band.
What development greatly reduces the number of voices reports on VHF com?
“Datalink” is a system where messages are sent and received in digital coding which is conversely reducing the number of voice transmission on VHF com.
What is the narrowest spacing for channels in VHF com band?
The narrowest spacing for channels in the VHF com band is 8.3333 kHz spacing
What is the purpose of the mic key line?
The Mic Key Line turns on the transmitter when a microphone button is pressed. Releasing the button switches the radio back to receive.
A typical com radio has two frequency displays; one for the ____ frequency, the other for the ______ frequency.
A typical com radio has two frequency displays; one for the active frequency, the other for the stored frequency.
What is the purpose of a squelch?
squelch allows atmospheric noise to be heard, which is an approximate test of whether the radio is operating.
What is the purpose does the “com test” control proivide?
The “Comm Test” is an automatic squelch which allows atmospheric noise to be heard, which is an approximate test of whether the radio is operating.
Where is the LRU for a com transceiver of a large aircraft located?
The line replaceable unit is located in the electronics bay in large aircrafts
What is a benifit of a radio management system?
A radio management system eliminates numerous knob, buttons and seperates control heads for operating com and nav radios. It’s less of a workload to operate and saves space on the instrument panel.
What are the two types of wire diagrams?
ASM - Aircraft schematic diagram
AWM - Aircraft wiring diagram
How many inputs and two outputs does the RS flip-flop?
The RS flip-flop has two inputs and two outputs.
A HIGH applied to the _____ input sets the output Q HIGH and output Q LOW.
A HIGH applied to the S (SET) input sets the output Q HIGH and output Q LOW.
A HIGH applied to the _____ input sets the output Q LOW and output Q HIGH.
A HIGH applied to the R (RESET) input sets the output Q LOW and output Q HIGH.
When does this RS flip-flop produce a high output on Q?
SET
RESET
UNKNOWN
SET
