Question

The following figure represents a superheterodyne receiver. Your target is to receive signals from a station which operates at 175 MHz. Find the image frequencies for your desired signals. Show your step by step calculation. Discuss the significance of image frequencies in communication systems. V Antenna RF amplifier First IF amplifier (30 MHz) Second IF amplifier (10 MHz) Detector and amplifier Output First local oscillator Second local oscillator COSW, او لما C05

Answer 1

Mixer 0 wo Cor) to wo do fd = with Mixer is down Converter case (1) fo > fs. fitz fo - fs.7 fo = fst fofi : 28175+30 fo.2 205 MHZ along with fs, we also receive the image frequency fi, at If, amplifier output fii = fet for 2175 + 2x30 = 125+60=235 MHZ At Mixer Case (1) fa > firi fifa= fd - fifi ofd z fohit for, z 10730 24OMA) 2

2 similarly when fs> to fff; e fs to fo.= fs - faf - 115-30 = 145 MHz along with fs, fiq (image fresuens) also passes fig = fs - af Ify -175-2430.-125-60 ZL15 MHZ :: fd is in the range . 2o < få < 40 MHz output of Ife is fig #fd) (115+ (20 to 40)) which is out of band od 10MHz, dence filtered out by IF2 (2nid IF). The significance of persoalan image frequency is, it results in crosstalk | interference

Communications, spectrum is divided of alloled to different application. so due to a Cross retalle resulted due to image frequency results in it losing the reliability of Communication,