Thread: Brainteaser
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Old May 26th 06, 10:14 PM posted to rec.radio.amateur.antenna
Cecil Moore
 
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K7ITM wrote:
Actually, it was "200 watts forward, 100 watts reflected" -- but it
works the same way: 100 ohm line, 1 second long: source is DC
200*sqrt(2) volts in series with 100 ohms. Load is such that it
absorbs 100 watts from that source: 100*(3 +/- sqrt(8)) ohms. About
17.16 ohms works OK. Then the line voltage is 41.42V and the energy
stored in the 1/100F line capacitance is 8.579 joules, and the line
current is 2.414A and the energy stored in the 100H line inductance is
291.421 joules. Total energy stored is 300 joules.


As can be seen from http://www.qsl.net/w5dxp/1secsgcr.gif

Do you think it's just a coincidence that 200 watts of forward
power in a one second long line would require 200 joules and
100 watts of reflected power in a one second long line would
require 100 joules for a total of 300 joules?

Now, I have no idea who it is that might be saying that there's no
energy stored in the fields in a line, so I really don't know what the
to-do is all about.


Please read what W7EL says about forward and reflected power
in his "food for thought" writings. In particular: "Some inventive
people have supposed they can separate forward and reverse power with
a circulator. That really sounds attractive, particularly with an open
or short circuited load. In that condition, the forward and reverse
powers are each 100 watts, yet the transmitter (or the transmitter
voltage source) doesn't have to produce any power at all."

What W7EL doesn't seem to realize is that the source produced the
power in the forward and reverse power waves while the feedline
was charging up during the transient period before the reverse power
waves reached the source so there is bona fide energy in those waves.
He also says there is no model for handling such yet one exists in
detail in the magazine article on my web page.
--
73, Cecil http://www.qsl.net/w5dxp