RF Receivers

RF receivers are electronic devices that separate radio signals from one another and convert specific signals into audio, video, or data formats. RF receivers use an antenna to receive transmitted radio signals and a tuner to separate a specific signal from all of the other signals that the antenna receives. Detectors or demodulators then extract information that was encoded before transmission. There are several ways to decode or modulate this information, including amplitude modulation (AM) and frequency modulation (FM). Radio techniques limit localized interference and noise. With direct sequence spread spectrum, signals are spread over a large band by multiplexing the signal with a code or signature that modulates each bit. With frequency hopping spread spectrum, signals move through a narrow set of channels in a sequential, cyclical, and predetermined pattern.

Selecting RF receivers requires an understanding of modulation methods such as AM and FM. On-off key (OOK), the simplest form of modulation, consists of turning the signal on or off. Amplitude modulation (AM) causes the baseband signal to vary the amplitude or height of the carrier wave to create the desired information content. Frequency modulation (FM) causes the instantaneous frequency of a sine wave carrier to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal. Amplitude shift key (ASK) transmits data by varying the amplitude of the transmitted signal. Frequency shift key (FSK) is a digital modulation scheme using two or more output frequencies. Phase shift key (PSK) is a digital modulation scheme in which the phase of the transmitted signal is varied in accordance with the baseband data signal.

RF receivers vary in terms of performance specifications such as sensitivity, digital sampling rate, measurement resolution, operating frequency, and communication interface. Sensitivity is the minimum input signal required to produce a specified output signal having a specified signal-to-noise (S/N) ratio. Digital sampling rate is the rate at which samples can be drawn from a digital signal in kilo samples per second. Measurement resolution is the minimum digital resolution, while operating frequency is the range of received signals. Communication interface is the method used to output data to computers. Parallel interfaces include general-purpose interface bus (GPIB), which is also known as IEEE 488 and HPIB Protocol. Serial interfaces include universal serial bus (USB), RS232, and RS485.

Additional considerations when selecting RF receivers include supply voltage, supply current, receiver inputs, RF connectors, special features, and packaging. Some RF receivers include visual or audible alarms or LED indicators that signal operating modes such as power on or reception. Other devices attach to coaxial cables or include a connector or port to which an antenna can be attached. Typically, RF receivers that are rated for outdoor use feature a heavy-duty waterproof design. Devices with internal calibration and a frequency range switch are also available.

RF receivers are used in a variety of applications and industries. Often, devices that are used with integrated circuits (ICs) incorporate surface mount technology (SMT), through hole technology (THT), and flat pack. In the telecommunications industry, RF receivers are designed to fit in a metal rack that can be installed in a cabinet. RF receivers are also used in radios and in electronic article surveillance systems (EAS) found in retail stores. Inventory management systems use RF receivers as an alternative to barcodes. 

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