TABLE OF CONTENTS The superheterodyne receiver (referred to hereafter as a superhet) is the most widely used receiver design for nearly all uses; ELINT applications included. A basic block diagram is shown in Figure 3.15. The idea is to use a local oscillator to convert the incoming signal to a fixed intermediate frequency by the mixing process (heterodyning). Then the IF amplifier need operate at only one frequency and its characteristics can be precisely controlled (gain, center frequency, bandwidth, band edge roll-off, group delay). The bandwidths for typical narrowband ELINT receivers are B RF ~ B IF ~ 20 MHz and B V ~ 10 MHz. This allows for good pulse fidelity for normal radar pulses (pulse width ~1 ?s). Such receivers were the mainstays of ELINT operations during World War II. More recent designs have additional capabilities. Rapidly sweeping the local oscillator in frequency produces an amplitude versus frequency display, which is created by displaying the amplitude detector output versus the tuning voltage, thus creating an RF spectrum analyzer. Very rapid sweeping creates a rapid sweep superhet, described in Chapter 9, which is useful for detecting high duty cycle, low power signals in the presence of low duty cycle interfering signals. Still more rapid sweeping is the basis of the microscan and metascan compressive receivers described later. Using very wide receiver bandwidths (e.g., 500 MHz to 2 GHz), and using a microwave IF (e.g., 2 GHz) creates a frequency conversion system which...
