Download - T 05 radio recivers
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Radio Receivers
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Overview
RX Power Reception Selection Demodulation Reproduction
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Rx
Types CW AM (SSB) FM
Crystal Tuned Radio Receiver Superhet
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RX
Functions Reception Selection Demodulation Reproduction
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Reception - Power
Inverse square law
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Reception - Power
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Reception
Aerial / antenna Polarisation Direction
Yagi array
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Reception
Sensitivity Weak signal noise
Selectivity Band width filter 1% of RX Frequency
Stability
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Reception
Crystal radio AM (not CW, SSB or FM) Poor sensitivity and selectivity
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Reception
Tuned radio Improves selectivity and sensitivity Amplifiers (difficult to stabilise)
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Reception
Superheterodyne Best selectivity, sensitivity and stability
(tuned oscillator)▪ CW, AM, SSB, FM
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Reception
1st stage Buffer Amplifier Filter
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Selection
Mixer Intermediate Frequency Smaller band width (5 kHz) – receiver bandwidth Local oscillator – controls reception frequency
fs – fo = fif
fs + fo = fif
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Selection
Image frequencies two frequencies can produce the same
IF
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Demodulation
CW and SSB AM FM
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Demodulation
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
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Demodulation
AM RX Detector
Envelope detector Product detector
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Demodulation
Envelope detector
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Envelope detector circuit
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Demodulation
Product detector Works for AM and SSB fif . flo
Filter result
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Demodulation
FM RX Quadrature detector▪ Multiply with signal phase shifted 90o
Phase Lock Loop (PLL)▪ Error signal
Digital Signal Processor
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Demodulation
FM RX Foster-Seeley Discriminator▪ Frequency control using a centre tapped
transformer
▪ Ratio detector
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Reproduction
Low Frequency amplifier
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Questions?