On Jun 9, 2:44*pm, Roy Lewallen wrote:
So the answer to your question is that the "reverse power" goes to
wherever the new excess "forward power" comes from. Once you figure out
where that is, you'll have a better understanding of the topic than
nearly everyone who has been arguing on this forum about it for years.

Let's be careful to point out that "forward power" is a measurement
*at a fixed point* on a transmission line of the rate of flow of the
forward energy which is traveling at the speed of light in the medium.
Same concept for "reflected power" - reflected energy flowing in the
reverse direction at the speed of light in the medium. EM waves cannot
stand still.

It's easy to figure out where the excess forward energy comes from
especially in an ideal lossless system which I will assume for the
rest of this posting. Consider the following thought experiment. An
ideal lossless system with a one-second long Z0=300 ohm feedline. Why
one-second long? Because the watts (joules/second) and the joules will
be the same magnitude, i.e. If it's a matched line with 100 watts of
forward power, it is easy to show that a one-second feedline has 100
joules of energy in it that has been sourced but not yet delivered to
the load - like a delay line.

Here's an example of a Z0-matched system with an SWR of 6:1 on the
Z0=300 ohm feedline. *Steady-state* conditions a forward power =
204 watts and reflected power = 104 watts. Power delivered to the load
= 100 watts. There is a steady-state Z0-match at '+'. Zero reflected
energy reaches the source, i.e. the SWR on the 50 ohm line is 1:1.

100w source---50 ohm line---+---1-sec-long 300 ohm line---50 ohm load

During the transient key-down state, the source supplies a number of
joules to the transmission line that do not reach the load. At the
beginning of steady-state that value is 204 joules plus 104 joules
equals 308 joules.

When steady-state is reached there are 308 joules of energy "stored"
in the one second long transmission line that have not been delivered
to the load. Only after the transmission line is charged with steady-
state energy does the load start to accept the same amount of power as
is being sourced. There is no magic here - just a simple accounting
for all the energy. Why otherwise intelligent, educated RF engineers
cannot perform that simple second-grade math is a subject for another
thread.

During steady-state, there are 308 joules of energy "stored" in the
transmission line that are performing the Z0-match function. There are
204 joules in the forward wave and 104 joules in the reflected wave.
Since RF cannot actually be stored as in a battery, this energy is
moving at the speed of EM waves - the speed of light in the medium.
104 joules/second is continuously being reflected at the load. 104
joules/second is continuously being redistributed back toward the load
at the Z0-match.

At key-up, steady-state ends and the key-up transient state occurs.
During this transient state, all of the 308 joules in the forward wave
and reflected wave during steady-state will be dissipated. During the
key-down transient state, 308 joules are stored in the one second long
transmission line. During the key-up transient state, the 308 joules
are dissipated. For those who feel overwhelmed, it is just simple
second-grade math

In a Z0-matched system, the entire analysis can be performed using an
energy analysis instead of a voltage analysis. The common way to
analyze the above system is to assume that 70.7 volts is present on
the 50 ohm side of the Z0-match with 1.414 amps flowing into the Z0-
match. But with only an energy analysis, we can reverse-engineer the
voltage and current conditions at any point in a Z0-matched system.

Fact of Physics: There are exactly enough joules of energy in the
mismatched transmission line to support the forward wave power and the
reflected wave power. It's not magic nor rocket science. Anyone
willing to count the joules that have not reached the load will
realize that the energy in the forward and reflected waves consists of
real-world joules that cannot be swept under the rug just because some
alleged RF guru is ignorant of the laws of physics.

Here's a simple math problem for all of the readers having trouble
with this concept. On 10 MHz, we have a 50 ohm antenna being fed with
one wavelength of lossless 300 ohm line from a 100w source. During
steady-state, how many microjoules of energy are "stored" in the
transmission line that have not yet reached the load? How are those
microjoules split between the forward wave and reflected wave?
--
73, Cecil, w5dxp.com