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An AM signal encodes the information onto the carrier wave by varying its amplitude in direct sympathy with the analogue signal to be sent. There are two methods used to demodulate AM signals.
The envelope detector is a very simple method of demodulation. It consists of anything that will pass current in one direction only, that is, a rectifier. This may be in the form of a single diode, or may be more complex. Many natural substances exhibit this rectification behaviour, which is why it was the earliest modulation and demodulation technique used in radio. The crystal set exploits the simplicity of the modulation to produce an AM receiver with very few parts.
The product detector multiplies the incoming signal by the signal of a local oscillator with the same frequency and phase as the carrier of the incoming signal. After filtering the original audio signal will result. This method will decode both AM and SSB, although if the phase cannot be determined a more complex setup is required.
Frequency modulationFM redirects here, for alternate uses, see Fm Frequency modulation (FM) is the encoding of information in either analogue or digital form into a carrier wave by variation of its instantaneous frequency in accordance with an input signal. This is typically or FM is more complex. It has numerous advantages over AM, such as better fidelity and noise immunity. However, it is much more complex to both modulate and demodulate a carrier wave with FM, and AM predates it by several decades.There are several common types of FM demodulator:
The Quadrature detector, which phasePhase from the Greek phasis meaning 'appearance', has a number of related meanings in English. The phase of a waveform is the position of any peak or trough compared to the same feature on a second waveform. A phase of matter is a physically distinctive f shifts the signal by 90 degrees and multiplies it with the unshifted version. One of the terms that drops out from this operation is the original information signal, which is selected and amplified.
The Foster-Seeley discriminatorThe Foster-Seeley discriminator is an FM detector circuit that works on the same principle as most commonly used FM detectors, which is through variations in frequency. It uses a twice-tuned RF transformer to convert frequency changes into amplitude chang.
The Phase-locked loopMany electronic systems use internal clocks which are required to be phase-aligned to and/or frequency multiples of some external reference clock. For example, a typical PC CPU of 2004 might have an internal 2. 4 GHz clock which is phase aligned to a bus
In addition, FM can be demodulated using a digital signal processorA digital signal processor (DSP is a specialized microprocessor designed specifically for digital signal processing, generally in real-time. DSPs can also be used to perform general-purpose computation, but they are not optimised for this function. Rather, a technique used in software defined radio.
ElectronicsElectronics is the study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The pure study of such devices is considered as a bra