On Mon, 26 Feb 2007 02:03:09 GMT, james wrote
in :

On Sat, 24 Feb 2007 22:22:56 -0800, Frank Gilliland
wrote:

+++This method has been used in the real world for many years, and it is still
+++being used. Better ways?
+++
+++
+++Several.
+++
+++Long story short, the power-to-voltage ratio of a signal is always
+++higher than the power-to-voltage ratio of noise. Most RF front ends
+++are voltage amps. But a -power- amp on the left can dig the signal out
+++of the noise on the order of 2-4dB, sometimes more. I like using a
+++common-base for the 1st RF, but you can re-bias a common emitter and
+++make pretty good improvements. And, as I stated before, a low input
+++impedance will reduce or eliminate the impedance transformation prior
+++to amplification.
************

That is true in most cases. Most of my RF work in the front end dealt
around using small loop antenna( less than 1/8 wave) for paging
recievers and those puppies have very low radiation resistance. You
need some impedance transformation even if you do use common base.


Well, yeah, with a 1/8 wave loop? LOL!

Anyway, a common base with a single transistor can get you in the
neighborhood of 100 to 500 ohms, depending on the transistor. With a
50 ohm input that leaves you with a transformation ratio from 2:1 to
10:1, which is -way- better than the typical 1000:1 to 10000:1 range
needed for a bipolar voltage amp (I won't even mention FET's). The
lower the ratio the better. Put two or three transistors in parallel
and you can divide that ratio down even further.

Take a half-hour or so and sift through your pile of schematics. I'm
sure you'll find a few radios that do this. Even some HF tube radios
used a grounded-grid triode on the front end -- not for stability as
might be assumed, but for performance.