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Build Your Own Transistor Radios by Ronald Quan

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Chapter 8Superheterodyne Radios

In Chapter 7 on regenerative radios we found that positive-feedback systems can enhance the selectivity and sensitivity for improved performance in a radio. Also, we found that for a regenerative radio, best performance was achieved when we added as much positive feedback or regeneration as possible, but just below the threshold of oscillation. When oscillation occurs in a regenerative radio, we lose performance.

The regenerative radio performs much better than “regular” tuned radio-frequency (TRF) radios, but it still has limitations because the selectivity is determined by the amount of regeneration added. For strong signals, the selectivity is less than when a weaker signal is tuned. The reason is that the weaker ...

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