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Modulation involves multiplying the input signal x(t) by a cosine with a frequency f2. Demodulation involves multiplying the modulated signal again by a cosine with a frequency f2, and then applying a low pass filter with cutoff frequency f2. The low pass filter removes the high frequency components centered about 2f2. Figure 19 Modulation
- Todays Topics
- Modulators
- DSB-SC vs. AM
- Modulation index
- Modulation Index Example
- Cat's Whiskers (Crystal) Radio
- Power of AM Signals
- 'AM(t) = (A + m(t)) cos(2 fct) = A cos(2 fct) + m(t) cos(2 fct)
- 2Pm ;
Modulators Typical Radio Receivers Commercial AM Envelope detection AM power Single Sideband AM (SSB) SSB idea SSB generation SSD detection
There are lots of ways to make modulators Often the problem is how not to make a modulator, say when you are designing an ampli er. We will look at some very common types Just about any non-linearity Multipliers such as choppers
DSB-SC modulated signals undergo phase reversal when m(t) changes sign. It is di cult to extract carrier from received signal.
The maximum deviation of m(t) from zero is mp = max(jm(t)j) The modulation index of the modulated signal is de ned by mp = A Larger modulation index reduces power but makes demodulation harder. Broadcast AM stations use modulation index close to 1. Input signals are controlled using automatic gain control (AGC).
This is an captured airband signal You can clearly see the carrier, and when it is keyed on and o . The rst transmission has a much higher modulation index than the second two. Why might this be? AM Demodulation Experiment
This radio was powered only by received radio energy. The point-contact semiconductor detector was subsequently resurrected around World War II because of the military requirement for microwave radar detectors.
The power of an AM signal is the sum of the power of two components.
| {z } | carrier {z } sidebands The carrier and sideband signals are orthogonal, so powers add. Carrier power is
where message power is average power as T gets large,
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These Recommendations for Radio Frequency and Modulation Systems, Part 1: Earth Stations and Spacecraft, were developed for conventional near-Earth and deep-space missions having moderate communications requirements.
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Sigma–delta modulation is the most popular form of analog-to-digital conversion used in audio applica-tions. It is also commonly used in D/A converters, sample-rate converters, and digital power amplifiers. In this tutorial the theory behind the operation of sigma–delta modulation is introduced and explained.
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For digital signals, there are several modulation techniques available. The three main digital modulation techniques are as follows: † Amplitude shift keying (ASK), † Frequency shift keying (FSK), and † Phase shift keying (PSK). Figure 1.4 illustrates the modulated waveforms for an input modulating digital signal.
Calculate the modulation index and percentage of modulation of an AM signal, given the amplitudes of the carrier and modulating signals. Define overmodulation and explain how to alleviate its effects.
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Jan 30, 2021 · In this chapter we will learn about frequency modulation (FM) of signals: linear (LFM), sinusoidal (SFM) and arbitrary. We will become familiar with generation of FM signals and their demodulation methods.
