EQPS - Radio Theory Flashcards
What use of radio is in ATC? (5)
- Voice Communication VHF/ UHF
- Navigation VOR /NDB
- Surveillance systems
- Weather radar
- Data transmission
What is Electricity? (1)
A form of energy produced by the movement of electrons in
atoms
What is Electro-magnetism? (1)
An electric current produces a magnetic field (B) perpendicular to the flow direction (I)
What are Radiowaves? (7)
- A form of electromagnetic energy that are similar in behavior to light waves
- Travel at 300,000,000 meters p/s (C)
- Can pass through a vacuum
- Travel in straight lines
- Invisible
- Intangible
- Inaudible without specialist equipment
What is Oscilation? (1)
When air moves backwards/forward (vibration) and the ear mimics the air which is moving. The receiving person hears a propagated tone
What is Audio limited by? (1)
Range
What is a Sine Wave? (1)
When a wave travels up, down and back to Zero - This is 1 cycle
What is Amplitude? (1)
The maximum displacement or value attained by the wave from it’s mean value during a cycle
What is Wavelength? (1)
The distance in meters or part of a meter between corresponding points in consecutive waves (Lambda ƛ)
What is Frequency? (1)
The rate of repetition of the cycle in one second where one cycle per second is known as one Hertz
How many Hertz in:
Kilohertz, Megahertz, Gigahertz
Kilohertz - 1Khz = 1000 Hz
Megahertz - 1 Mhz = 1,000,000 hz
Gigahertz - 1 Ghz = 1,000,000,000 Hz
What is Velocity (C)?
A constant electromagnetic wave at 300,000,000 meters p/s in a Vacuum
How do we get a lower frequency? (1)
A longer wavelength
How do we get a Higher frequency? (1)
A Shorter wavelength
What is the formula for calculating Velocity (C)? (1)
Frequency x Wavelength
What is a Carrier wave? (1)
An electro-magnetic wave which can be
modulated (varied) and is produced by a device called “The Local Oscillator”
How does Modulation work? (1)
When a carrier wave is varied in direct proportion to the signal that is to be transmitted…
…Modulation can change the amplitude or frequency of the carrier wave
How is a Carrier Wave modulated? (1)
Audio signal fed into a Modulator…
…Combines the carrier wave with the audio wave
What does FM stand for? (1)
Frequency Modulation
What does AM stand for? (1)
Amplitude Modulation
AM Modulation Diagram
FM Modulation Diagram
What are the Advantages of FM? (3)
- Resillience to noise
- Easy to apply modulation at a low power
- Use of efficient RF amplifiers
What are the Advantages of AM? (2)
- Stronger stations can override weaker / interfering stations
- A squeal (Heterodyne) will be heard > if both Tx’s are received with identical signal strength
What type of wave is sent to an Antenna? (1)
A Modulated carrier wave
What is a half-wave aerial? (1)
When using the top of a positive part of a cycle (Using a portion of the Wavelength)
e.g. small A/C aerials
What happens when you halve the wavelength? (1)
Power must be doubled to get the same range
How does EMF radiate? (1)
Perpendicular to the atenna
Vertical Antenna = Horizontal EMF
Horizontal Antenna = Vertical EMF
What does the RF AMP do? (2)
- Makes signal stronger
- Amplifies static noise (Consequence)
What is Static filtered out by? (1)
Noise Gate
What does a Demodulator do? (2)
- Earth’s out the carrierwave
- Audio part remains > fed into an audio amplifier
What happens to the signal when fed into an Audio Amplifier? (3)
- Signal fed into coil of wire around speaker magnet
- Diaphragm moves > air displaced to/from original frequency & amplitude
- Original sound is heard
