Chapter 12Introduction to Software-Defined Radios (SDRs)
Chapter 11 presented a different type of superheterodyne radio—a coil-less receiver. Two new concepts were introduced—image signals and switching-type radio-frequency (RF) signal mixers. It was also in Chapter 11 that image signals were shown to be eliminated or attenuated by providing a band-pass filter prior to RF mixer so that the desired signal is output from the mixer and not the image signal. In the coil-less radio, a higher intermediate frequency (IF) of 600 kHz was used with a 1.6-MHz low-pass filter to provide image signal rejection. The coil-less radio is rather simple to implement with integrated circuits.