Amplitude and Frequency Modulation

• Modulation converts data by adding information to an electronic or optical carrier signal into radio waves.
• A carrier signal has a steady waveform, constant height/amplitude, and frequency Modulation.

Amplitude and Frequency Modulation

• Wavelength is the distance between identical points on consecutive waves.
• Amplitude is the distance between the origin and crest or trough.
• Frequency measures the number of waves that pass a point per unit of time.
• The amplitude or height of the carrier wave is changed via Amplitude Modulation.
• The frequency of the carrier wave travel speed is changed via Frequency Modulation.

AM vs FM

Signal Transmission

• Radio Detection and Ranging (RADAR) tracks and fixes the location of targets at a distance using radio waves.
• Light Amplification by Stimulated Emission of Radiation (LASER) emits light through optical amplification based on the stimulated emission of electromagnetic radiation.
• The lasing medium produces the stimulated emission of photons in a laser.
• Stimulated emission releases energy from an excited atom by artificial means.
• Optical Resonators are mirrors facing each other.

Concepts

• Amplitude is the maximum displacement or distance moved by a point on a vibrating body from its resting.
• Wavelength is the distance between successive crests of a wave.
• Wave frequency is the number of waves that pass a fixed point in each amount of time.
• Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light.
• Transmission is the process of sending and propagating an analog or digital signal using wired, optical, or wireless electromagnetic medium.
• A transmitter generates and transmits electromagnetic waves carrying messages or signals.
• Modulation changes the parameters of the carrier signal in accordance with the instantaneous values.
• Demodulation extracts a carrier wave's original information-bearing signal.
• A receiver separates the desired radio frequency signal from all the other signals picked up by the antenna, then amplifies it and recovers the desired information.

Radio Receiver Circuit

• An Antenna captures a radio signal
• The RF (radio frequency) amplifier amplifies the radio signal
• The Tuner extracts particular signals
• The detector separates audio from the carrier wave
• The Audio amplifier amplifies the signal
• The Speaker outputs the sound

Classification of Radio Receivers

• Tuned Radio Frequency Receiver (TRF): A type of receiver that consists of a tuned circuit and a detector.
• Supersonic heterodyne radio receiver

TRF

• The first radio receiver used, was used early in wireless technology
• High sensitivity allowing broadcast frequency
• From 535 kHz to 1705 kHz RF. is high sensitivity allowing broadcast frequency

TRF Tuning and detection

• Changes the frequency through mechanical or electrical means.
• Tuned circuits can select one station, as well as improve selectivity.
• The detector reconstructs information carried by radio waves.
• Demodulation extracts the original information from the carrier wave.
• A diode, a capacitor, and a resistor make up the detector circuit, removing high-frequency components.

Supersonic Heterodyne Wireless Receiver

• Developed to provide an additional level of selectivity. This uses a heterodyne or mixing process to convert signals to a fixed intermediate frequency.

Heterodyne Components

• RF amplifier: Transmits IF signal and amplifies
• Mixer: Generates an output signal which contains the sum and difference of the frequency
• Local oscillator: Provides a signal to mix with signals coming from an antenna
• IF AMP and Filter: Amplifies the signal and rejects unwanted

FM Signal Receiver Block Components

• RF amplifier amplifies the radio signals
• Mixer combines tuning signals with RF from the antenna
• Local Oscillator produces the oscillator signal mixed with the incoming RF signal in a mixer stage.
• IF Amp and Filter, prevents interfering signals to enter the radio tuner when it is tuned to one radio station.
• The section of Intermediate Frequency filters
• Limiter
• Discriminator
• De-emphasis network
• AF and power amplifiers

Demodulator and Audio Amplifier

• Demodulator extracts the receiver's original modulation.
• Audio amplifier then amplifies the demodulated audio signal to drive a speaker.

AM radio Alignment

• Align intermediate frequency (IF) transformers to the receiver's correct intermediate frequency (IF).
• Align the input tuned circuits to match the scale/dial markings such that the wanted station or frequency is producing the correct value of intermediate frequency (IF)