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This stage provides a constant level of signal to the FM demodulator stage, reducing the effect of input signal level changes to the output. If two or more signals are received at the same time, a high-performance limiter stage can greatly reduce the effect of the weaker signals on the output. This is commonly referred to as the FM capture effect.
The Foster–Seeley discriminator [1] [2] is a common type of FM detector circuit, invented in 1936 by Dudley E. Foster [3] and Stuart William Seeley. The Foster–Seeley discriminator was envisioned for automatic frequency control of receivers, but also found application in demodulating an FM signal.
A wideband FM signal can also be used to carry a stereo signal; this is done with multiplexing and demultiplexing before and after the FM process. The FM modulation and demodulation process is identical in stereo and monaural processes. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. In broadcast ...
The output across the diodes is connected to a large value capacitor, forming a dynamic limiter. The ratio detector has the advantage over the Foster–Seeley discriminator that it does not respond to amplitude modulation (AM) signals, thus potentially saving a limiter stage; however, the output is only 50% of the output of a discriminator for ...
Demodulation is the process of extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave. [1] There are many types of modulation, and there are many types of ...
The capture effect can occur at the signal limiter, or in the demodulation stage for circuits that do not require a signal limiter. [1] Some types of radio receiver circuits have a stronger capture effect than others. The measurement of how well a receiver rejects a second signal on the same frequency is called its capture ratio.
A major category of AM demodulation technique involves envelope detection, since the envelope of an AM signal is the original signal. A diode detector is a type of simple envelope detector. It consists of a diode connected between the input and output of the circuit, with a resistor and capacitor in parallel from the output of the circuit to ...
Frequency modulation synthesis (or FM synthesis) is a form of sound synthesis whereby the frequency of a waveform is changed by modulating its frequency with a modulator. The (instantaneous) frequency of an oscillator is altered in accordance with the amplitude of a modulating signal. [1] FM synthesis can create both harmonic and inharmonic sounds.