CHOICE OF INTERMEDIATE FREQUENCY

• IMAGE REJECTION RATIO : Pick up due to local oscillator radiation from TV receiver

• Easy to separation modulating signal from IF carrier at the demodulator =

  Radio receiver IF frequency 455KHZ and audio frequency 5KHZ , in TV receiver higher modulating frequency 5MHZ and IF frequency 40 MHz

• Image frequency should not lie in FM band =

  FM band 88MHZ to 110MHz Intermediate frequency 40MHZ ,

  Image frequency lower VHF band 121 to 148MHZ

• Interface and direct pickup from band assigned for other service = Industry application frequency 21 to 27MHZ and intermediate frequency 40MHZ

• Gain = Intermediate frequency 40MHZ 625 B signal adopt in India which picture IF 38.9MHZ , sound IF 33.4MHZ USA picture IF 45.75MHZ , sound IF 41.25MHZ