Question 6A397

The selectivity of a receiver refers to its ability to differentiate between desired signals and unwanted signals on nearby frequencies. * **Superheterodyne receivers** offer the best selectivity. They achieve this by converting the incoming radio frequency (RF) signal to a fixed, lower intermediate frequency (IF). At this IF stage, highly selective, fixed-tuned filters (often crystal or ceramic filters) with a high Q factor can be used to precisely filter out unwanted signals, providing excellent and consistent selectivity across the tuning range. * **Tuned Radio Frequency (TRF) receivers** are less selective than superheterodynes. They use multiple tuned RF amplifier stages, all tuned to the incoming signal frequency. While multiple stages improve selectivity over a single stage, maintaining high and consistent selectivity across a broad tuning range is challenging because all stages must be precisely ganged and tracked, and their Q factors vary with frequency. * **Superregenerative receivers** have the poorest selectivity. They operate by using a single stage of controlled regeneration, bringing the circuit almost to the point of oscillation. This method offers high sensitivity with very few components but inherently results in very broad-band reception, making them prone to picking up multiple signals simultaneously and offering very poor rejection of adjacent frequencies. Therefore, in order of best to worst selectivity, the ranking is Superheterodyne, Tuned Radio Frequency, Superregenerative.