John S wrote:
On 7/6/2015 11:01 AM, Jerry Stuckle wrote:
On 7/6/2015 4:20 AM, Ian Jackson wrote:
In message , rickman writes
How about we quit with the speculation and come up with some numbers?
Here is a simulation of a 50 ohm load with a 50 ohm matched series
output impedance and a voltage source of 200 VAC peak. Power into the
load is 100 W.
http://arius.com/sims/Matched%20Load%20Power.png
Same exact circuit with the series impedance of just 1 ohm, power into
the load is 385 W.
http://arius.com/sims/UnMatched%20Load%20Power.png
I'd say that is pretty clear evidence that matched loads are not the
way to maximize power transfer when the load impedance is fixed and
the output impedance is controllable.
Quite simply, if your prime objective is to get maximum power out of a
power (energy?) source, the source having an internal resistance is a
BAD THING. You don't design the source to have an internal resistance
equal to its intended load resistance. No one designs lead-acid
batteries that way (do they?), so why RF transmitters?
While theoretically you can extract the maximum power available from the
source when the load resistance equals the source resistance, you can
only do so provided that the heat you generate in the source does not
cause the source to malfunction (in the worst case, blow up).
Because DC power transfer is not the same as AC power transfer.
Why not? Does something happen to the laws of physics with AC?
Yes, quite a lot, you get a whole new set of laws.
Capacitors are an open circuit at DC and have a frequency dependant
impedance at AC.
Inductors are a short circuit at DC and have a frequency dependant
impedance at AC.
There is no such thing as a transmission line at DC.
Current at DC is constant and does not cause propagation while current
at AC causes a varying electromagnetic field that can propagate.
There is no such thing as a phase angle at DC.
A wire carrying DC current will not induce a voltage into another nearby
wire but a wire carrying AC current will.
More?
--
Jim Pennino