"Richard Clark" bravely wrote to "All" (27 Feb 05 23:49:44)
--- on the heady topic of " Say what you mean."

RC From: Richard Clark
RC Xref: aeinews rec.radio.amateur.antenna:26138

RC On Mon, 28 Feb 2005 06:28:24 GMT, "George, W5YR"
RC wrote:

IF the Thevenin source approach worked, we would have to be content with max
50% efficient amplifiers. We know we can do better than that substantially.

RC Hi George,

RC I know you won't appreciate this, but it is a telling, simple test of
RC a practical situation with a practical Amateur grade transistor model
RC 100W transmitter commonly available for more than 20-30 years now:
RC 1. Presuming CW mode into a "matched load" (any definition will do);
RC 2. Report the DC power consumed before hitting the key;
RC 3. Report the DC power consumed while holding the key.

RC Concurrently note:
RC A. Report Heat Sink Temperature for a previously idle/rcv condition;
RC B. Report Heat Sink Temperature after 10 minute key-down.

RC For a hypothetical "100W" model (again, a contemporary, common example
RC for Amateur use) available through standard commercial venues:
RC 2. About 20W - 30W
RC 3. About 200W - 250W
RC A. About 20 degrees C (or room temperature)
RC B. Well above 37 degrees C (or skin temperature)

RC Now, if we are to be any judge of efficiency (Thevenin does not have
RC to be invoked, condemned, or venerated); then it runs close to 50%
RC (110%). Others can invoke their favorite deity to explain.


The maximum power transfer 50% efficiency Po/Pin figure is only valid
for a "linear" amplifier termed Class A (current flows through the
whole cycle). Other amplifier classes were invented which improved on
that 50%. i.e. Class B (push-pull) can approach just shy of 70%
(current flows through 50% of cycle), and Class C close to 90%
(current flow less than 50% of cycle). Did I misunderstand the
problem?

A*s*i*m*o*v

.... "Beware of all enterprises that require new clothes." -- THOREAU