Radio Theory Flashcards
What is electricity
A form of energy produced by the movement of electrons in atoms
What is Ampere’s law?
An electric current produces a magnetic field perpendicular to the flow direction
Radio waves are a form of electromagnetic energy that are similar in behaviour to light. True or False?
True.
How fast do radio waves travel?
300 million metres per second
Can radio waves travel through a vacuum?
Yes
How do radio waves travel?
Generally in a straight line
Can you hear radio waves?
No they’re inaudible without specialist equipment
What is a cycle?
The wave travelling from 0, up, down and back to 0
What is amplitude?
The maximum displacement or value attained by the wave from its mean value from the cycle.
(The further away it moves from 0 along the x-axis)
What is a wavelength?
Distance in metres or part of a metre between corresponding points in consecutive waves
What symbol represents wavelength?
Lambda symbol
Define Frequency
The rate of repetition of the cycle in one second.
One cycle per second is known as one hertz.
Frequency is represented by which symbol?
F
A kilohertz (1KHz) is equal to how many hertz?
1,000Hz
One megahertz (1MHz) is equal to how many hertz?
1,000,000 Hz
One Gigahertz (1GHz) is equal to how many hertz?
1,000,000,000 Hz
Longer wave length is lower frequency.
True or False?
True.
Shorter wavelength is a higher Frequency.
True or False?
True or False?
What is the equation for Velocity (C)?
C=F x lambda
Velocity=Frequency x Wavelength
What device modulates carrier waves?
The local oscillator
What can be modulated?
Amplitude or Frequency
What does AM and FM stand for?
Amplitude Modulation
Frequency Modulation
How does a Modulator (local oscillator) work?
The audio signal is fed into the modulator which combines the carrier wave and audio wave.
What are the advantages of Frequency Modulation (FM)?
1) Resilience to Noise
2) Easy to apply Modulation at low power
3) Use of efficient radio frequency amplifiers
What are the advantages to Amplitude Modulation (AM)?
1) Stronger stations can override weaker stations
2) A heterodyne (sequel) heard if both stations are transmitting simultaneously.
Which Modulation is used to broadcast ATC RTF?
AM as it doesn’t require excellent audio clarity
Reducing the size of an aerial can be made possible by transmitting a portion of the wavelength. True or False?
True.
Using what part of the cycle is known as Half-wave aerial?
The top of the positive wave.
Using what part of the cycle is known as quarter wave aerial?
90 degrees of the cycle
If you only use half the wave what must you do to the power to get the same range?
Double the power
The electromagnetic field radiates___________ to the antenna
Perpendicular
Signals received will be very weak and will need to be_______
Amplified
What does the amplifier do?
Makes the signal stronger
Down side amplifies any noise, has no “noise gate”
What does the demodulator do?
It earths the carrier wave out and feeds audio wave into Audio speaker
How does the speaker relay the audio wave?
Signal fed into coil wire around the speaker magnet. In turn, moving the diaphragm of the speaker.
