[ARC5] How Edwin Armstrong invented the superhet

[1oldlens1]

A comment. A regeneration has two advantages for CW: the first is that as it approaches oscillation it becomes narrower in selectivity.  When it begins to oscillate the oscillation acts as a BFO  There is a critical adjustment just at the point of oscillation where the bandwidth is minimum   More feedback will begin to broaden it out more.   At minimum feedback the gain is minimum and bandwidth maximum.  Note that the change in gain and bandwidth is confined to the regenerative stage.  Pre selector stages are nor affected.  I don't remember the theory but the change in gain with feedback is probably not linear.  In any case old RDF sets are likely TRF. I believe I have schematics for both Kolster and Radiomarine RDF receivers in some very old books.  The main thing is to be able to here the variation in signal strength as the antenna is rotated. Precision measurement is not necessary, only thr relative variation with direction.  Actually only the null is of interest.   There were schemes of adding regeneration to an IF stage to make it narrower and to make it oscillate so as to act as a BFO .  The relatively crude circuit used in the S-38B and later,and SW-54 are examples.  This arrangement is strictly an economy.  The original S-38 has one more tube than the later versions.Sent from my Galaxy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20230107/348ddf43/attachment.html>