Variable channel tuning filter and equivalent circuitb

The tuner's output intermediate frequency is divided into two types: one is high and medium frequency (for example, 402.78 MHz), and the other is low intermediate frequency (for example, 134.26 MHz).
For the high- and medium- frequency tuner, the input filter is a low-pass filter, whose function is to suppress out-of-band image interference and the power
leakage of local oscillator 2. The amplifier before mixing can be composed of a 2-stage resistor-capacitor or choke-type negative feedback wideband amplifier. For low and medium-rated tuners, the
input filter is a variable channel tuner or variable image cutoff filter, as shown in Figure 6-43. This circuit is a 2-stage dual-tuned amplifier
variable channel tuning filter. devices , respectively formed by capacitive coupling and inductive coupling.