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