On 24 mayo, 21:30, Cecil Moore wrote:
On May 24, 3:06*pm, lu6etj wrote:

For example this part = "by inserting a pad having 15 to 20 dB
I give the following example: If we load a generator directly with a
resistance of 10 ohms, without any transmission line, there are not
traveling waves interfering, therefore there are not stationary waves,

Yes, standing waves are hard to visualize, but there is indeed same-
cycle interference involving forward waves and reflected waves. There
is a certain delay from the source signal to the load and back that
can be calculated if one chooses. The wave reflection model is closer
to Maxwell's equations than is the lumped-circuit model where EM waves
propagate instantaneously. Maybe the concepts presented in the
following paper would help. There is no transmission line for a Tesla
coil but reflection effects still exist. The lumped circuit model, to
which you allude, incorrectly assumes that signals can travel at
faster than the speed of light, an obvious impossibility.

http://www.ttr.com/corum/index.htm

Incidentally, this is the reason that W8JI measured a 3 ns delay
through a foot-long 75m loading coil. There were same-cycle
reflections existing in a near-infinite SWR situation. In such a
configuration, the phase of the current doesn't change at all yet W8JI
assumed the measured phase change was proportional to the delay
through the coil. Nothing could be farther from the technical truth.
--
73, Cecil, w5dxp.com


Hi Cecil. thank you very much for your answer. (I am a "fan" of your
rationale and very practical multiband open wire antenna feeding and I
do not know why it is no so popular as G5RV in my country).
.....
I know a model is necessary false by definition because is only a
model (an approximation to the hipothetical "real thing"), but I do
not imagine what is the tranmission line in the source-load
combination of my idealized model circuit example. I am not capable to
judge validity of idealized circuit theory in general to this example,
neither. Please, could you tell me which would be the transmission
line Zo in my resistive divider example?

Anyway, my question is about validity of the assertion that reflected
wave -in that example- IS ABSORBED by the pad. According to my simple
calculations this hipothesis, as I see it, it does not coincide with
my early learnings.

For example, with a 2 V generator with Zs=1 ohm, Zc=4 ohms and Zo=1
ohm, Pc is 0.64 W. Then Pf =1 W (as Owen says in his article), Pr=0.36
W. Rendering Ef=1 V, and Vf=0.6V. Summing both in phase gives 1,6 V on
the line-in point (same as on load point).
These are the same power and voltages values that simple resistive
divider predicts. The system fulfills the Kirchoff law and all power
(as we learn in circuits theory) it flows from source to load.
In the example I suggest a half wave transmission line loaded with 4
ohms it is at practical effects indistinguishable from a 4 ohms
resistive load directly connected to generator. What would be the
reflected power that would be dissipating in Zs (or the pad)?

This is not opposed to the conjugate mirror principle explained,
neither other propositions given in the cited article. IMHO reflected
power never "returns into" generators when they are active (and in
steady state); reflected power it is re-reflected in conjugated match,
and vectorially composed to render a load impedance to the generator
when this is directly connected to the line (when there is not any
matching devices inserted).
I do not suggesting that reflected power is "virtual" or any similar
thing, of course if we insert a circulator to separate both powers,
generator now would see 1 ohm load, could develope 1 W incident, 0 W
reflected (Pn=1W) on circulator input, 0.36 W would be outputting on
the other port to render 0.64 W (Pn) to the load with 1 W Pf and 0,36
W Pr again.

If I am in error please give me your explanations.

73

Miguel ghezzi LU6ETJ