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GATE 2016 EC (EC3) – Question 31

Communications · Analog Communications · 1 mark · Numerical answer

A superheterodyne receiver has intermediate frequency 15 MHz and local oscillator frequency 3.5 GHz. The received signal is above the oscillator frequency. The image frequency in MHz is ________.

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Correct answer: 3485 to 3485

Explanation

Both a signal above and a signal below the oscillator by the same intermediate frequency produce the same mixer difference frequency.

The desired signal is 3500+15=3515 MHz. Its image lies on the other side, at 3500−15=**3485 MHz**. It is separated from the desired signal by twice the intermediate frequency, 30 MHz.

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