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"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 |
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