Modullation of Radio Wave – Ibex Aviation Academy

Modulation

Modulation is the process of super imposing intelligence on the carrier wave
Carrier wave is capable of travelling long distances due to its high frequency and energy
Amplitude and frequency of a carrier wave remains constant
Signal wave is a low energy wave containing voice or data intelligence
Modulation is the process of attaching the signal wave on to carrier wave for transmission

Keyed modulation is the the simplest form of modulation where intelligence is sent by switching on and off the carrier wave
Morse code is an example of Keyed Modulation

Amplitude modulation is the process of modifying the amplitude of carrier wave according to the amplitude of signal wave
AM Radio Transmissions are examples of Amplitude Modulation

Frequency modulation is the process of modifying the frequency of carrier as per the amplitude of the signal
FM Radio is an example of Frequency Modulation and requires a wider band width as compared to AM

Phase Modulation is the process of modifying the phase of the carrier wave
Phase modulation can be Analogue or Digital Phase Modulation
Analogue Phase Modulation modifies phase of carrier by short time frequency changes
Digital phase modulation or Phase shift keying modifies phase of carrier using binary numbers
Digital phase modulation has superior noise reduction and reduce fading
GPS and MLS use Phase Shift Keying technology

Pulse modulation is the process of transmitting carrier in short pulses
Radar and Data link systems use pulse modulation
Pulses transmitted are of accurately measured and of very short duration
Duration of pulses are measured in microseconds and intervals between pulses are measured in milliseconds

The process of modulating the carrier wave is called Heterodyning
Heterodyning produces Upper and Lower Side Bands
Band width is the range of frequency bands occupied by a modulated wave
Frequency range of a modulated wave extends from the sum to the difference between carrier and signal frequencies

Depth of Modulation is a measure of voice clarity of transmission
DDM is calculated as a ratio between maximum and minimum amplitudes of the transmission
Formula for Depth of Modulation = (Max – Min) / (Max + Min) x 100

Band width is the range of frequency bands occupied by a modulated wave
Heterodyning is the process of modulation that produces Upper and Lower Side Bands
Double side band (DSB) modulation transmits both the side bands to the receiver
Single side band (SSB) modulation suppresses the lower side band before transmission
SSB Transmission requires lesser power since the power is concentrated in upper side band
DSB requires higher transmission power since it has to be distributed between both the side bands
SSB reduces frequency usage due to narrow bandwidth and accommodates more channels
SSB Transmissions suffer from lower interference due to higher power of transmission

Doppler principle is used to measure the relative velocity of a moving object
Doppler shift is the change in frequency due to relative movement between the transmitter and receiver
Radio aids like Airborne doppler calculate relative velocity by measuring the Doppler Shift
Doppler shift is the product of transmitted frequency and relative velocity divided by speed of light
Doppler Shift = (Transmitted Frequency x Relative Velocity) / Speed of Light