Amplitude Modulation, AM Tutorial Includes:
Amplitude modulation, AM AM basic theory & formulas AM bandwidth & sidebands Modulation index & depth AM efficiency AM demodulation / detection Diode detector Synchronous detector AM modulators Single sideband, SSB SSB demodulation
Modulation formats: Modulation types & techniques Frequency modulation Phase modulation Quadrature amplitude modulation
Demodulation is a key process in the reception of any amplitude modulated signals.
Demodulation is the process by which the original information bearing signal, i.e. the modulation is extracted from the incoming overall received signal.
The process of demodulation for signals using amplitude modulation can be achieved in a number of different techniques, each of which has its own advantage.
The demodulator is the circuit, or for a software defined radio, the software that is used to recover the information content from the overall incoming modulated signal.
Detection or demodulation
The terms detection and demodulation are often used when referring to the overall demodulation process. Essentially the terms describe the same process, and the same circuits.
Terms like diode detector, synchronous detector and product detector are widely used. But the term demodulation tends to be used more widely when referring to the process of extracting the modulation from the signal.
The term detection is the older term dating back to the early days of radio.
The term demodulation is probably more accurate in that it refers to the process of demodulation, i.e. extracting the modulation from the signal.
That said both terms can be used equally well, although modern terminology tends to err towards the use of the words demodulation and demodulator.
AM demodulation techniques
There are a number of techniques that can be used to demodulate AM signals. Different types are used in different applications to suit their performance and cost.
- Diode rectifier envelope detector: This form of detector is the simplest form, only requiring a single diode and a couple of other low cost components. The performance is adequate for low cost AM broadcast radios, but it does not meet the standards of other forms of demodulation. Read more about diode envelope detector.
- Product detector: It is possible to demodulate amplitude modulated signals with a receiver that incorporates a product detector of mixer and a local beat frequency oscillator or carrier injection oscillator. In its basic form, the local oscillator is not synchronised to the incoming signal carrier.
- Synchronous detection: Synchronous detection provides the optimum performance. It uses a mixer or product detector with a local oscillator signal that is synchronised to the incoming signal carrier. This provides many advantages over the other methods of AM demodulation. Read more about synchronous detector.
More Essential Radio Topics:
Radio Signals Modulation types & techniques Amplitude modulation Frequency modulation RF mixing Phase locked loops Frequency synthesizers Passive intermodulation RF attenuators RF filters Radio receiver types Superhet radio Radio receiver selectivity Radio receiver sensitivity Receiver strong signal handling
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