Question

4. A superheterodyne radio receiv er is required to cover the VHF frequency band from 70-85 MHz, using an intermediate frequency (IF) of 10.7 MHz. a) Find the frequny range needed fromthe local oscillator. b) Determine whether all image frequencies will be outside the operating frequency band.

Answer 1

Summary - it is basic problem so I have shown step by step solution .
f_L0 = f)s plusminus F_IF f_L0 = Local oscillator freq. f_s = (70 - 85 Mhz) f_IF = 10.7 MHz f_L0 = 70 plusminus 107, 85 plusminus 10.7 f_L0 = 80.7 MHz, 95.7 MHz 59.3 MHz 74.3 MHz \r\n 1) Image frequency f_Image = f_L0 + f_IF f_L0 = 80.7 MHz f_IM_1 = 90 - 7 MHz outside f_L0 = 59.3 MHz f_IM_2 = 70 MHz inside f_L0 = 95.7 MHz f_IM_3 = 105.7 MHz outside f_L0 = 74.3 MHz f_IM_4 = 8.5 Mhz inside