Filtering and Second-Order distortion As a general rule, we place a band-pass filter between the antenna and the first active element of a receiver to restrict the number of signals applied to the...

Filtering and Second-Order distortion As a general rule, we place a band-pass filter between the antenna and the first active element of a receiver to restrict the number of signals applied to the first active element (see Figure 7-57). By restricting the number of signals applied to the receiver, we reduce the chance that strong signals can combine in a nonlinear fashion to produce unwanted distortion products that will affect signals in the receiver’s passband. For a commercial FM broadcast receiver that covers 88.1 to 108.1 MHz, what combination of input signals sets the upper and lower limits ( fLOW and fHIGH) of the preselection filter? In other words, to find fLOW , examine the spectrum below the preselection filter’s passband. Find the two highest-frequency signals that could combine via a second-order process to produce a signal that falls in the receiver’s passband. To find fHIGH, examine the spectrum above the preselection filter’s passband. Find the two lowest-frequency signals that could combine via a second-order process to produce a signal that falls in the receiver’s passband.

Figure 7-57