Cecil Moore wrote in news:fuWFh.3131$M65.1761
@newssvr21.news.prodigy.net:

Cecil Moore wrote:
Owen Duffy wrote:
This simple example that shows that existence of "reflected power" on
a transmission line does not necessarily result in some or all of the
"reflected power" being dissipated in the generator.

I will leave it to Cecil to take to confuse this simple example with
some photon based complication.

No photons necessary, Owen. You are using a Thevenin
equivalent source.

What is the dissipation in the generator using a Norton
source?

The existence of cases that show that dissipation in the source does not
necessarily increase due to VSWR on the transmission line does not
support the assertion that "VSWR causes reflected power that is
dissipated in the source". One sound case is enough to disprove the
generality.

Sure, transforming the source to a Norton equivalent would produce an
answer, and in this case a different answer for what happens inside the
generator. That Norton equivalent source with half wave s/c line will
also produce zero dissipation in the source.

Cecil, it appears your motive is to create confusion to divert attention
from the cases that are inconsistent with the assertion that "VSWR causes
reflected power that is dissipated in the source".

I have no difficulty with the statement "a transmitter is usually
specified to work over a limited range of load impedances (often
specified as a maximum VSWR at the transmitter terminals), the user
should expect it works properly over that range and should understand
that operation outside of that range may expose it to voltages or
currents (consequent heat), that may cause permanent damage". This advice
can be given to a six hour ham without telling them any lies, but
imparting the knowledge that they need to operate safely.

The explanation expressed / supported by some here that "we use ATUs to
cause total re-reflection of power "reflected" from the antenna so
protecting the PA" is a nonsense explanation of how the ATU protects the
PA from the effects of a poor load.


Owen

Owen Duffy wrote:
Cecil, it appears your motive is to create confusion to divert attention
from the cases that are inconsistent with the assertion that "VSWR causes
reflected power that is dissipated in the source".

Appearances can be deceiving. My motive is to uncover facts
and I agree with virtually everything you have said.

My personal opinion is that from 0% to 100% of reflected
power can be dissipated in the source depending upon the
relative phase of the incident reflected wave and the
configuration of the source. It can be argued that if the
source sees an infinite or zero impedance, then all of the
source power is reflected at the source output. This, of
course, would be a same-cycle reflection, something that
also occurs at the mismatched load.

By convention, any power same-cycle reflected at the source
output was never generated to start with - one of the original
copouts.

Since the great majority of amateur transmitters are
looking into a Z0-match resulting in total destructive
interference in the direction of the source, IMO, this
subject is pretty much moot. That's why I poke fun at it.

All one has to do to calculate the reflected power
dissipated in the source is to understand the constructive
and destructive interference occurring at the source
output terminal. This is easier said than done.
--
73, Cecil http://www.w5dxp.com