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.
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
Draw out the rest of this RS Flip Flop
answer
This RS flip-flop is constructed from two _____ gates.
This RS flip-flop is constructed from two NOR gates.
Explaiin what happens when a HIGH applied to input S and a LOW applied to input R.
The HIGH input on S is applied to gate B and inverted to a LOW output. Any HIGH input to a NOR gate will produce a LOW output.
The output of gate B is used as a feedback signal to the input of gate A.
The LOW input on R is applied to gate A. The two LOW inputs of gate A are inverted, producing a HIGH output on Q.
The output of gate A is used as a feedback signal to the input of gate B.
Notice that, even if the inputs are removed, the feedback signal from gate A will hold the Q output LOW. Remember, any HIGH input produces a LOW output.
The flip-flop must remain in the SET state until a HIGH is applied to the RESET input.
Draw out a JK Flip Flop
JK flip-flops have five inputs (yellow) and two outputs (green).
What’s the difference between these two flip flops?
Positive and negative edge
