transreceiver-trasnsmiter receiver and frequency sysnthesizer
transceivers are electronic devices that receive and demodulate radio frequency (RF) signals, and then modulate and transmit new signals. They are used in many different video, voice and data applications. RF transceivers consist of an antenna to receive transmitted signals and a tuner to separate a specific signal from all of the other signals that the antenna receives. Detectors or demodulators extract information that was encoded before transmission. Radio techniques are used to limit localized interference and noise. To transmit a new signal, oscillators create sine waves which are encoded and broadcast as radio signals.
Selecting RF transceivers requires an understanding of modulation methods and radio techniques. 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. On-off key (OOK), the simplest form of modulation, consists of turning the signal on or off. 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. In terms of radio techniques, some RF transceivers use direct-sequence spread spectrum. Others use frequency-hopping spread spectrum.
Important specifications for RF transceivers include data rate, sensitivity, output power, communication interface, operating frequency, measurement resolution, and maximum transmission distance. Data rate is the number of bits per second that can be transmitted. Sensitivity is the minimum input signal required. Communication interface is the method used to output data to computers. General-purpose interface bus (GPIB) is the most common parallel interface. Universal serial bus (USB), RS232 and RS485 are common serial interfaces. Operating frequency is the range of signals that can be broadcast and received. Measurement resolution is the minimum digital resolution. Maximum transmission distance is the largest distance by which the transmitter and receiver can be separated. Additional considerations when selecting RF transceivers include power source, supply voltage, supply current, transmitter inputs, receiver inputs, and RF connector types.