Radio recivers

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Radio receivers for FRO

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Radio recivers

  1. 1.  RX  Power  Reception  Selection  Demodulation  Reproduction
  2. 2.  Types  CW  AM (SSB)  FM  Crystal  Tuned Radio Receiver  Superhet
  3. 3.  Functions  Reception  Selection  Demodulation  Reproduction
  4. 4.  Inverse square law
  5. 5.  Aerial / antenna  Polarisation  Direction  Yagi array
  6. 6.  Sensitivity  Weak signal  noise  Selectivity  Band width filter  1% of RX Frequency  Stability
  7. 7.  Crystal radio  AM (not CW, SSB or FM)  Poor sensitivity and selectivity
  8. 8.  Tuned radio  Improves selectivity and sensitivity  Amplifiers (difficult to stabilise)
  9. 9.  Superheterodyne  Best selectivity, sensitivity and stability (tuned oscillator) ▪ CW, AM, SSB, FM
  10. 10.  1st stage  Buffer  Amplifier  Filter
  11. 11.  Mixer  Intermediate Frequency  Smaller band width (5 kHz) – receiver bandwidth  Local oscillator – controls reception frequency fs – fo = fif fs + fo = fif
  12. 12.  Image frequencies  two frequencies can produce the same IF
  13. 13.  CW and SSB  AM  FM
  14. 14.  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
  15. 15.  AM RX  Detector  Envelope detector  Product detector
  16. 16.  Envelope detector
  17. 17.  Envelope detector circuit
  18. 18.  Product detector  Works for AM and SSB  fif . flo  Filter result
  19. 19.  FM RX  Quadrature detector ▪ Multiply with signal phase shifted 90o  Phase Lock Loop (PLL) ▪ Error signal  Digital Signal Processor
  20. 20.  FM RX  Foster-Seeley Discriminator ▪ Frequency control using a centre tapped transformer ▪ Ratio detector
  21. 21.  Low Frequency amplifier

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