> We know that negative feedback in audio amplifiers improves linearity and
> reduces distortion. What would it take to improve RF linears with
> feedback? In thinking about it for a bit (not enough time, no doubt). It
> seems that RF feedback will introduce lots of problems with stability
> because the feedback will vary in phase over frequency...producing an
> oscillator. Linearizing the envelop might improve things, but it doesn't
> do anything about the phase component...might even worsen it.
Grounded grid amplifiers already have a very high level of almost
perfect negative feedback as long as the grid is properly grounded.
Some tubes have long grid leads that add some amount of
uncontrolled feedback, and some amplifiers add some uncontrolled
feedback through intentional "floating" of the control grid through
low value capacitors.
> In the commercial world, broadband, low IMD amplifiers use feed forward
> techniques...precompensate the input to produce a clean output. The
> principle seems clear but how it applies to a bandswitched amp and how a
> ham with just a grid dipper can set it up seems murky.
You can add negative feedback to a grid driven tetrode with the
addition of an unbypassed resistor in the cathode.
73, Tom W8JI
w8ji@contesting.com
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