# Receivers

### Explanation of question 13

The possibilities of second channel interference in a superheterodyne receiver can be reduced by

- i two IF stages - a first low IF stage followed by a second high IF stage
- ii good screening of the mixer
- iii high selectivity in the RF amplifier

1. ii and iii only
2. i and iii only
3. i and ii
4. i, ii and iii

The answer is :- 1 Two if. stages, each at different frequencies, will give the advantage of low possibility of second channel interference and increased selectivity. The first stage must have a high if. to lessen the possibility of second channel interference. High selectivity is then achieved by the second low i.f., therefore i is wrong. ii and ill both aid the reduction of second channel interference.

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