Modern Instrumentation Final Project AM/FM Radio

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Modern Instrumentation Final Project AM/FM
Radio

• Zhou Brian

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AM Signal Processing

• Amplitude modulation (AM) is a technique used in
  electronic communication, most commonly for
  transmitting information via a radio carrier wave

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AM Modulation

• Include the original information of signal to a
  carrier wave
• Carrier wave
• first order component of signal
• AM signal

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Frequency range 500Khz-1.6MhZ
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AM Demodulation

• Extract the message from the AM wave
  Rectification
• Ideal diode and capacitor to rectify AM signal
  and to extract the envelop wave
• Capacitor here is for discharging process and it
  has to be relatively large in order to discharge
  very slowly
• Half wave rectification/Full wave
  rectification(use diode bridge to utilize both
  sides of the AC signal)

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Circuits
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Explanation

• BJT needs a low voltage power supply which is
  around 1.5 v(voltage across 2 diodes)
• Signal out of diode is the envelop but with a
  small amplitude(50 mv, not enough fan-out to
  drive next stage)
• According to chip datasheet , connect control
  capacitance to get a larger gain

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(No Transcript)
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Experimental Results
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Frequency Modulation (FM)

• Whats it all about?

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How does FM carry information?

• FM, as its name suggests, varies the frequency
  around a carrier wave
• i.e. a carrier wave is what you tune into on your
  radio at its carrier frequency
• The signal is put into the carrier wave during
  transmission (broadcasting)
• Carrier wave frequency range is between 80-110MHz
  (VHF)

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Some FUN!
Xm is the signal
This is the carrier wave.
TRANSFORM!!!
fD is the deviation from the carrier
wave frequency (fc)
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What FM Looks Like
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How do you pull the signal out?

• One way is to use a Foster-Seeley discriminator
• This converts your FM signal into AM
• Part of a process called slope detection which
  converts amplitude changes to sound
• HOWEVER, pulling a signal out this way does not
  reduce noise (compared to the AM receiver)

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Super Regenerative Detector

• In this type of FM detection, there are two types
  of oscillations at work through a regenerative
  amplifier
• The primary oscillation is the carrier frequency
  (resonance) fed into the amplifier, and the
  secondary oscillation is for pulling out the
  signal
• The secondary is operated at ultrasound levels to
  avoid audio interference
• This is not possible for AM due to the secondary
  lying in the audio range

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FM Radio SchematicSuperRegenerative
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Summary

• AM signal is easier to demodulate (extract the
  message), but it needs more power when
  transmitting the signal and noise is manifest in
  the signal compared to FM.
• FM has better quality of sound ,noise immunity,
  and consumes little power in signal transmission,
  however the demodulation part is harder, we need
  convert the very high frequency into sound which
  is in a low frequency range. So in order to do
  that, we have to use multiple stages of
  amplifier frequency converter(mixer)

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The Future!

• Continue working on FM receiver
• Implement full wave rectification (bridge) for AM
  receiver and compare quality of signal
• Work on transmitting signals (walkie-talkie)
• Radio Telescope
• Mission to Mars