This whole discussion points out the fallacy of trying to understand
reflections by sending a CW signal. Consider a 100W pulse radar transmitter.
Also, assume the transmitter rurns off between pulses ( a good assumption),
and that the antenna mismatch causes 3% of the power to be reflected.

When the pulse reaches the antenna, 97W is transmitted, and 3W is returned.
All of this 3 W is reflected by the transmitter, and a second pulse is
produced where 2.91W is radiated and .09 W is reflected back. This is
re-reflected, and a third pulse is produced where .0873 W is radiated and
..0027 W is reflected, etc, etc.

Tam/WB2TT
"W5DXP" wrote in message
...
William E. Sabin wrote:
Keeping everything simple and not getting into peripheral issues is
desirable at this point.

The assumption that the source is outputting (forward power
minus reflected power) is essentially saying that all amplifiers
are perfectly matched and re-reflect all reflected power.
That seems like a stretch to me.
--
73, Cecil http://www.qsl.net/w5dxp



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Tarmo Tammaru wrote:
This whole discussion points out the fallacy of trying to understand
reflections by sending a CW signal.

There is nothing wrong with considering the
steady-state solution. We do that all the time.
The steady-state is achieved mathematically by
considering an infinite sum of forward and
reflected waves (for a CW signal) until it
converges to a steady state. In the final solution
the source impedance is found to have no effect on
the standing wave pattern (the SWR).

Reference: W.C. Johnson "Transmission Lines and
Networks", McGraw-Hill 1950, chapter 4, Equation 4.23.

In the steady state the final result is according
to my discussion.

Bill W0IYH

On Fri, 18 Jul 2003 09:47:32 -0400, "Tarmo Tammaru"
wrote:
Consider a 100W pulse radar transmitter.

Hi Tarmo,

Was this a speculation or borne of actual experience? (I am not
talking about the obvious, exceptionally low power.)

I understand the significance of what you wrote following it,
.0027 W is reflected, etc, etc.
but in my experience with radars (megawatt models that I serviced,
calibrated and offered formal training in), this does not happen.

73's
Richard Clark, KB7QHC

Call it a simple example. I would assume in a real system multiple pulses
are would be highly undesirable and eliminated by discharging the line at
the end of the first pulse. Maybe I should have said 100W pulse generator
with on output impedance of 0 or infinity, and a lousy dummy load. At a
lower power you could hook up a 'scope to the middle of the line and see the
multiple reflections.

Tam/WB2TT
"Richard Clark" wrote in message
...
On Fri, 18 Jul 2003 09:47:32 -0400, "Tarmo Tammaru"
wrote:
Consider a 100W pulse radar transmitter.

Hi Tarmo,

Was this a speculation or borne of actual experience? (I am not
talking about the obvious, exceptionally low power.)

I understand the significance of what you wrote following it,
.0027 W is reflected, etc, etc.
but in my experience with radars (megawatt models that I serviced,
calibrated and offered formal training in), this does not happen.

73's
Richard Clark, KB7QHC

On Fri, 18 Jul 2003 15:41:21 -0400, "Tarmo Tammaru"
wrote:

Call it a simple example. I would assume in a real system multiple pulses
are would be highly undesirable and eliminated by discharging the line at
the end of the first pulse. Maybe I should have said 100W pulse generator
with on output impedance of 0 or infinity, and a lousy dummy load. At a
lower power you could hook up a 'scope to the middle of the line and see the
multiple reflections.

Tam/WB2TT

Hi Tam,

I would call your Radar a faulty example.

The point of the matter is that real equipment exhibits real
dissipation of reflected power in the conventional expectation. Your
new example above anticipates this by forcing a failure of that
expectation through not matching the load.

Such problems that arise as a consequence were written up by NBS,
Hewlett-Packard and Steven Adams in the discussion of Mismatch
Uncertainty.

The fact that various pundits and savants have no actual value to
offer in substitution for the oft-repeated refrain "it a'in't 50Ohms"
is that any value offered would be immediately demonstrated as being
wrong through standard bench top verification.

As Ian has characterized this as an exercise in futility, I am content
to observe no one stepping up to the bench for validation.

73's
Richard Clark, KB7QHC