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Modern Instrumentation Final Project AM/FM Radio

Modern Instrumentation Final Project AM/FM Radio. Zhou & Brian . AM Signal Processing. Amplitude modulation ( AM ) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM Modulation.

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Modern Instrumentation Final Project AM/FM Radio

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  1. Modern Instrumentation Final ProjectAM/FM Radio Zhou& Brian

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

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

  4. Frequency range 500Khz-1.6MhZ

  5. 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)

  6. Circuits

  7. 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

  8. Experimental Results

  9. Frequency Modulation (FM) What’s it all about?

  10. 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)

  11. Some FUN! Xm is the signal This is the carrier wave. TRANSFORM!!! fD is the deviation from the carrier wave frequency (fc)

  12. What FM “Looks” Like

  13. 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)

  14. 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

  15. FM Radio SchematicSuperRegenerative

  16. 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)

  17. 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

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