Posted on Aug 4, 2012 12536
The local oscillator is crystal-controlled and the i-f swing is hardly compressed. The deviation of the transmitted carrier frequency, because of modulation, must therefore be limited to prevent severe distortion of the demodulated audio signal. The component values result in an i-f of 4.5 kHz and an i-f bandwidth of 5kHz. If the i-f is multiplied ll`f N, the values of capacitors Cl7 and Cl8 in the all-pass filters, and the values of illter capacitors C7, CS, ClO, Cll, and Cl2 must be multiplied by 1/N.
For improved i-f selectivity to achieve greater adjacent channel attenuation, second-order networks can be used in place of ClO and Cll.