Receiver System Parameters
A receiver picks up the modulated carrier signal from its antenna. The carrier signal is downconverted, and the modulating signal (information) is recovered. Figure 5.1 shows a diagram of typical radio receivers using a double-conversion scheme. The receiver consists of a monopole antenna, an RF amplifier, a synthesizer for LO signals, an audio amplifier, and various mixers, IF amplifiers, and filters. The input signal to the receiver is in the frequency range of 20–470 MHz; the output signal is an audio signal from 0 to 8 kHz. A detector and a variable attenuator are used for automatic gain control (AGC). The received signal is first downconverted to the first IF frequency of 515MHz. After amplification, the first IF frequency is further downconverted to 10.7 MHz, which is the second IF frequency. The frequency synthesizer generates a tunable and stable LO signal in the frequency range of 535–985 MHz to the first mixer. It also provides the LO signal of 525.7 MHz to the second mixer.
Other receiver examples are shown in Fig. 5.2. Figure 5.2a shows a simplified transceiver block diagram for wireless communications. A T/R switch is used to separate the transmitting and receiving signals. A synthesizer is employed as the LO to the upconverter and downconverter. Figure 5.2b is a mobile phone transceiver (transmitter and receiver) . The transceiver consists of a transmitter and a receiver separated by a filter diplexer ...