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Regeneration and LC tuning circuits.

Ernst Erb Otmar Jung 
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Papers » Principles of schematics etc. » Regeneration and LC tuning circuits.
Joe Sousa
Joe Sousa
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25.Mar.10 05:09

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Fellow Radiophiles,

Mr. Hans Knoll and Prof. Rudolph have explored a central topic in regenerative receivers in the German language side of the forum. They discuss the effect of positive feedback, or regeneration, on LC tuning circuits I read their posts with Google-Translate.

The essential idea of the discussion is that the response, or selectivity, of the LC tuning circuit in a regenerative receiver does not change with regeneration or positive feedback. The combined response of the original LC tuning circuit and regeneration yields the familiar improvement in selectivity and gain.

This important insight is relevant to the design of regenerative receivers.

Two recent threads explore the design or regenerative receivers:

1- Wolfgang Holtman compares the Armstrong method of regeneration to that used by Von Bronk. Wolfgang demonstrates experimentally how important the Q of the LC circuit is, before regeneration is applied, in particular for the Armstrong method. I read this German language article with Google-Translate.

2- Bryce Ringwood shares his design of a regenerative receiver, and regeneration methods are explored.

A general conclusion can be drawn from these designs, and that is that it is important to start with an LC tank circuit that has as high a Q (quality factor) as possible.

One reason for this is that less regeneration is needed to achieve the same output level.

A small amount of regeneration (or positive feedback) is much easier to control than a large amount of regeneration.

One way to understand this is that a poor LC tuning circuit has a heavy loss, and requires a large amount of regeneration. The optimum regeneration will be obtained when the regeneration is just enough to make up for almost all of the high losses of the low quality LC tuning circuit, without oscillations. We are dealing here with balancing two large quantities, and any slight variation in the LC losses, or regeneration can make the circuit oscillate.

Sometimes a high Q LC tank circuit performs poorly because of excessive loading by the grid leak resistor in the grid circuit. In this case, the apparent Q of the LC tank circuit will be much lower due to loading by grid conduction.



This article was edited 25.Mar.10 20:26 by Joe Sousa .