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process of shifting the frequency spectrum of a signal is called modulation. As an example human voice spans a 4 kHz range or bandwidth, and is centered at 0 kHz. In order to transmit human voice over a cell phone, the transmitter shifts the voice signal so that it has a 4 kHz
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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Modulation is a process whereby the characteristics of a wave (the carrier) are varied in accordance with a mes-sage signal, the modulating waveform. Frequency translation is usually a by-product of this pro-cess. Modulation may be continuous, where the modulated wave is always present, or pulsed, where no signal is present between pulses.
- 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,
Jan 16, 2015 · This chapter provides an overview of analog modulation and frequency modulation (FM). Information is encoded through a variation of the phase of the carrier wave in phase modulation (PM).
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Digital modulation (or channel encoding) is the process of converting an input sequence of bits into a waveform suitable for transmission over a communication channel. Demodulation (channel decoding) is the corresponding process at the receiver of converting the received waveform into a (perhaps noisy) replica of the input bit sequence.
