This document summarizes the key components and functions of radio receivers. It discusses the types of modulation used in radio including CW, AM, and FM. It then describes the main components of radio receivers including the antenna, tuner, mixer, oscillator, and demodulator. It explains how superheterodyne receivers provide the best selectivity, sensitivity and stability by shifting signals to an intermediate frequency for processing before detection and amplification.

2.  RX
 Power
 Reception
 Selection
 Demodulation
 Reproduction

3.  Types
 CW
 AM (SSB)
 FM
 Crystal
 Tuned Radio Receiver
 Superhet

4.  Functions
 Reception
 Selection
 Demodulation
 Reproduction

5.  Inverse square law

7.  Aerial / antenna
 Polarisation
 Direction
 Yagi array

8.  Sensitivity
 Weak signal
 noise
 Selectivity
 Band width filter
 1% of RX Frequency
 Stability

9.  Crystal radio
 AM (not CW, SSB or FM)
 Poor sensitivity and selectivity

10.  Tuned radio
 Improves selectivity and sensitivity
 Amplifiers (difficult to stabilise)

11.  Superheterodyne
 Best selectivity, sensitivity and stability (tuned
oscillator)
▪ CW, AM, SSB, FM

12.  1st stage
 Buffer
 Amplifier
 Filter

13.  Mixer
 Intermediate Frequency
 Smaller band width (5 kHz) – receiver bandwidth
 Local oscillator – controls reception frequency
fs – fo = fif
fs + fo = fif

14.  Image frequencies
 two frequencies can produce the same IF

15.  CW and SSB
 AM
 FM

16.  Beat Frequency Oscillator
 Mixes with IF to produce an audio tone
 |fif – fbf |= Beat Frequency
 fif + fbf remove using a filter
 Used in SSB and CW (no carrier wave)
 Change crystal to change sideband

17.  AM RX
 Detector
 Envelope detector
 Product detector

18.  Envelope detector

19.  Envelope detector circuit

20.  Product detector
 Works for AM and SSB
 fif . flo
 Filter result

21.  FM RX
 Quadrature detector
▪ Multiply with signal phase shifted 90o
 Phase Lock Loop (PLL)
▪ Error signal
 Digital Signal Processor

22.  FM RX
 Foster-Seeley Discriminator
▪ Frequency control using a centre tapped transformer
▪ Ratio detector

23.  Low Frequency amplifier