Cecil, W5DXP wrote:
"Would you publish an example?"

I am error prone as anyone reading many of my postings may attest. The
1955 edition of Terman`s "Electronic and Radio Engineering" is the
culmination of about 25 or more years of Terman`s work which was
checked, rechecked, then checked again. It`s stood the test of time ever
since its publication too. In Sect. 4-11 are answers to questions of
impedance matching to transmission lines.

I think Terman should be consulted straight away for a simple logical
cause of no reflections. It is called impedance matching. The match does
away with reflections.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Cecil, W5DXP wrote:
"Would you publish an example?"

I am error prone as anyone reading many of my postings may attest. The
1955 edition of Terman`s "Electronic and Radio Engineering" is the
culmination of about 25 or more years of Terman`s work which was
checked, rechecked, then checked again. It`s stood the test of time ever
since its publication too. In Sect. 4-11 are answers to questions of
impedance matching to transmission lines.

I'll look up the book next time I am at Texas A&M.

I think Terman should be consulted straight away for a simple logical
cause of no reflections. It is called impedance matching. The match does
away with reflections.

Not directed at Richard, but I've seen the following logic used
often with EM waves.

What causes the match? The cancellation of reflections.

What causes the cancellation of reflections? The match.

Does anyone else detect the circular logic problem in the above?

Another one:

'rho' is zero because there are no reflections.

There are no reflections because 'rho' is zero.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"What causes the match? The cancellation of reflections."

This is like Abbot and Costello. You got it! Who`s on first!

You have a source which only delivers energy at a certain volts to amps
ratio, period!

You have a load which only accepts energy at a certain volts to amps
ratio, period!

When the above ratios are in fact identical there is no problem. When
the above ratios are different something has to give and it isn`t either
ratio, Zo or ZL. Instead, the load takes what the source can deliver and
rejects the surplus volts or amps whichever is the case, as are created
by ZL, and the limited deliverability created by the Zo. The surplus
generates a reflected wave as Cunningham recounted with his description
of missing inductance and capacitance in the missinng continuation of
the transmission line (A short on the line vitiates the capacitance
etc.). The explanation is logical and I recommend his broadcast antenna
book.

What`s not to understand about matching? When the load is not matched,
you add the incremental receptivity required to take the surplus current
or voltage at the load, so that the load, and the stub in Terman`s
example, are a perfect match and there is no longer any surplus to be
reflected. The impedance of the load has been adjusted, by the addition
of a stub in Terman`s example, to Zo. Terman says the wave from the stub
cancels the wave from the mismatched load. No doubt a shorted stub makes
a reflection. The reflected volts from the stub are exactly equal and
opposite to the reflected surplus volts from the load at the junction,
and Terman says there is no reflection toward the generator.

I never won an argument with Terman, though I tried. I believe there is
no reflection past the stub back toward the generator. If so, and it
certainly is so, I`ve put those stubs out at the antenna myself and they
create a match when adjusted properly, the energy on a lossless line
will be the same at the generator and anywhere on lhe line. It`s flat.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
What`s not to understand about matching?

The energy and momentum in EM waves, particularly, the energy and
momentum in the wave reflected from a mismatched load. What happens
to that energy and momentum? We know it joins the forward wave. How
does that energy and momentum get reversed? A virtual impedance is
a result and not the cause of anything.

The reflected volts from the stub are exactly equal and
opposite to the reflected surplus volts from the load at the junction,
and Terman says there is no reflection toward the generator.

I'm not arguing that point. What happens to the energy in the two waves
that have their voltage and current amplitudes equal in amplitude and
opposite in phase? There is no doubt those waves cancel and there is
no reflection toward the generator. But what happens to the intrinsic
energy that pre-existed the cancellation event?

I never won an argument with Terman, though I tried. I believe there is
no reflection past the stub back toward the generator.

No argument about that. The question is where did the energy and momentum
go when those two waves were canceled thus eliminating reflections back
toward the generator. Waves can be canceled. The energy in those waves
cannot be destroyed.
--
73, Cecil http://www.qsl.net/w5dxp



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