On Jun 6, 10:22*am, "JC" wrote:
Basic question (at least for me) for a very poor antenna matching :
-100 w reach the antenna and 50 w are radiated.
- 50 w are "reflected", what is their fate ?
Are they definitely lost for radiation and just heat the line, the final.....
JC

I assume that your numbers were obtained using a directional
wattmeter,
that is, forward power is 100W, 50W are reflected and by subtraction,
it is computed that 50W enter the antenna, some of which is dissipated
in the antenna losses and some of which is radiated.

The 100W forward and 50W reflected have no relation to actual powers
but
are simply values that are constructed so that when they are
subtracted
the result is the average power flowing towards the load.

From these numbers alone it is impossible to decide whether the system
is operating as it should or to compute where the losses might be, or
whether there are any losses at all. With an appropriate antenna tuner
it is entirely possible that the transmitter is delivering its design
output of 50W to the line and all of this energy is reaching the
antenna and being radiated.

Thus the whole question of "where does the reflected power go?", is
rather misleading.

....Keith

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From HP Journal V.7n.2:

If an incident wave is applied at
the left as shown in the diagram, the
wave passes down the main arm. In
the region where the lines are cou
pled, a wave 20 db below the inci
dent wave will be coupled to the
"Forward" terminal, while a second
wave 20 db below the incident wave
will be coupled to the resistive ter
mination in the "Reverse" arm.
Since the combined power in the
two split-off waves amounts to only
2% of the power in the main wave,
the main wave is essentially unalt
ered and continues to the right-hand
terminal.
A wave applied at the right end
of the coupler is coupled in an analo
gous manner. Waves 20 db below the
left-traveling wave will be coupled
to the "Reverse" terminal and to the
resistive termination in the "For
ward" arm, while the main part of
the wave continues to the left-hand
terminal.
The couplers thus provide equal
fractions of right-traveling and left traveling
waves at separate termin
als. The ratio of these waves will be
equal to p *, the magnitude of the
reflection coefficient of any device
connected to the output of the cou
pler. This ratio can be measured
(Fig. 4) by applying the outputs of
the "Forward" and "Reverse" ter
minals to the -hp- 416A Ratio Meter,
using suitable detectors to demodu
late the amplitude-modulated power
which must be used with the system.
In an ideal directional coupler, no
power from a forward wave would
be received at the reverse terminal
and no power from a reverse wave
would be received at the forward ter
minal. In practice some undesired
power is received at these terminals,
although it has been possible to de
sign the couplers so that this unde
sired power is at least 46 db below
the parent wave, i.e, at least 26 db
below the desired wave at the oppo
site terminal. In other words the di
rectivity of the couplers is at least
26 db (30 db in the lower frequency
couplers) over the complete fre
quency range [Fig. 3(a), (b)].
The coupling mechanism itself
consists of quarter-wavelength sec
tions of the conductors placed suit
ably near one another to achieve the
desired degree of coupling. The
combined effects of electrical and
magnetic coupling impart directiv
ity to the coupled wave. The unused
terminal of each of the auxiliary
arms is terminated in a special widerange
low-reflection resistor to ab
sorb any power coupled to that ter
minal.

73's
Richard Clark, KB7QHC

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From HP Journal V4n5-6:

The multi-hole coupler design has now
been extended to a 3 db coupler, that is, a
coupler in which half the power entering the
main guide is coupled into the auxiliary
guide.
....
The -hp- multi-hole couplers consist of
two sections of wave guide mutually coupled
by two rows of coupling holes (Fig. 2).
Power entering the input arm of the coupler
flows down the main guide and divides at the
coupling mechanism. Part of the power con
tinues down the main guide where it will be
incident on any device connected at the end
of the guide. The other part of the power is
coupled into the auxiliary guide. It is a prop
erty of directional couplers that the power
coupled into the auxiliary guide flows essen
tially in only one direction. In the -hp- coup
ler, this power flow is in the same direction
as the power in the primary guide.
....
R E F L E C T O M E T E R S E T - U P
....
Two directional
couplers are connected back-to-back
as shown.
*******
I will leave it to the readership to imagine why.

73's
Richard Clark, KB7QHC

On Jun 6, 9:34*pm, Richard Clark wrote:
On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart

wrote:
The 100W forward and 50W reflected have no relation to actual powers

From HP Journal V4n5-6:

The multi-hole coupler design has now
been extended to a 3 db coupler, that is, a
coupler in which half the power entering the
main guide is coupled into the auxiliary
guide.
...
The -hp- multi-hole couplers consist of
two sections of wave guide mutually coupled
by two rows of coupling holes (Fig. 2).
Power entering the input arm of the coupler
flows down the main guide and divides at the
coupling mechanism. Part of the power con
tinues down the main guide where it will be
incident on any device connected at the end
of the guide. The other part of the power is
coupled into the auxiliary guide. It is a prop
erty of directional couplers that the power
coupled into the auxiliary guide flows essen
tially in only one direction. In the -hp- coup
ler, this power flow is in the same direction
as the power in the primary guide.
...
R E F L E C T O M E T E R * S E T - U P
...
Two directional
couplers are connected back-to-back
as shown.
*******
I will leave it to the readership to imagine why.

73's
Richard Clark, KB7QHC

Walter was the first to place things in a book and a book is the first
point of reference in this newsgroup
Nothing personal Richard, but it is obvious that engineers are totally
split as to what theorem is correct and the one to be used. There is
no way
you will get agreement if they all insist their position is correct
and thus other positions are not worth consideration.You may be
correct in your position but the idea of change is not in your favor.

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From HP Journal V.3n7-8

DIRECTIONAL couplers have been used
widely in wave guide applications for
such purposes as monitoring power, meas
uring reflections, mixing, and for isolation
of signal sources. All of these applications
make use of the property that power flowing
in one direction in the main branch of the
coupler induces a power flow in only one
direction in the auxiliary circuit.

73's
Richard Clark, KB7QHC

On Jun 7, 1:37*am, Richard Clark wrote:
All of these applications
make use of the property that power flowing
in one direction in the main branch of the
coupler induces a power flow in only one
direction in the auxiliary circuit.

Power flow??? Heaven forbid.
--
73, Cecil, w5dxp.com

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From HP Journal V.6n.1-2:

Power from the source flows down
the main arms of the two couplers
(Fig. 2) and impinges on the load.
The power split off by the 20 db
forward coupler is all passed to the
forward detector, since the directiv
ity characteristic of the multi-hole
directional couplers prevents any
but a negligible amount of the splitoff
power from turning back and
being absorbed in the coupler's in
ternal termination. The power split
off the incident wave by the 10 db
reverse coupler, however, is essen
tially all absorbed in that coupler's
internal termination because of the
reversed direction of connection of
that coupler (Fig. 2).
If the magnitude of the reflection
coefficient ~.T. of the load is, say, 0.1,
Çf of the incident voltage will be
reflected back toward the source. As
this reflection passes back through
the main arm of the reverse coupler,
a 10 db split occurs and is applied
to the reverse detector. The remain
der of the reflection will proceed
back toward the generator where it
will be absorbed in the generator
impedance and in the termination
in the forward coupler.

********

Of course, in regard to this last sentence, HP engineers didn't know
jack-**** about power reflections, especially what could be absorbed
by the source.

73's
Richard Clark, KB7QHC

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From a current NARDA specification:

GENERAL COUPLER OPERATION
A coaxial directional coupler has the general appearance
of a section of coaxial line, with the addition of a second
parallel section of line and with one end terminated (see
Figure 9). These two sections are known as the main and
auxiliary lines. The two lines are internally separated from
each other; the amount of spacing between lines determines
the amount of RF energy that may be transferred
from the main line to the auxiliary line. In operation, assume
that energy is fed into port A of the main line. Most of
this energy will appear at output port B of the main line.
However, a fraction of this energy (determined by coupling
value) will also appear at the coupled port C, of the
auxiliary line.
A dual-directional coaxial coupler, such as the
reflectometer coupler, consists essentially of two single-
ended couplers connected back-to-back. Perhaps
the most important characteristic of the directional coupler
(and the one from which its name originates) is its
directivity.
....
For reflectometry applications,
the dual directional coupler, incorporating two
auxiliary outputs, permits the simultaneous sampling of incident
and reflected power.
....
RF power applied to
the load is reflected to some degree depending on load
characteristics, thereby resulting in a voltage standing
wave ratio (VSWR) which is reflected back to the main line
output port. this reflected power is coupled out of the reflected
output port at a level 10 dB down from the reflected
power level at the load.

73's
Richard Clark, KB7QHC

On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From MECA, makers of Isolators - their application:

The isolator is placed in the measurement path of a test bench between
a signal source and the device under test (DUT) so that any
reflections caused by any mismatches will end up at the termination of
the isolator and not back into the signal source. This example also
clearly illustrates the need to be certain that the termination at the
isolated port is sufficient to handle 100% of the reflected power
should the DUT be disconnected while the signal source is at full
power. If the termination is damaged due to excessive power levels,
the reflected signals will be directed back to the receiver because of
the circular signal flow.
....
MECA offers twenty-four models of isolators and circulators in both N
and SMA-female connectors with average power ratings from 2 - 250
watts.

73's
Richard Clark, KB7QHC

On Jun 8, 3:47*am, Richard Clark wrote:
On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart

wrote:
The 100W forward and 50W reflected have no relation to actual powers

From MECA, makers of Isolators - their application:

The isolator is placed in the measurement path of a test bench between
a signal source and the device under test (DUT) so that any
reflections caused by any mismatches will end up at the termination of
the isolator and not back into the signal source. This example also
clearly illustrates the need to be certain that the termination at the
isolated port is sufficient to handle 100% of the reflected power
should the DUT be disconnected while the signal source is at full
power. If the termination is damaged due to excessive power levels,
the reflected signals will be directed back to the receiver because of
the circular signal flow.
...
MECA offers twenty-four models of isolators and circulators in both N
and SMA-female connectors with average power ratings from 2 - 250
watts.

Good day Richard,

You have located several examples from reputable vendors where the
behaviour of directional couplers is described in terms of power
in a forward and reflected wave. This model of behaviour works within
its limits and allows for convenient computation and prediction of
the behaviour. But all of these papers have the appropriate
discipline and do not ask the question "where does the reflected
energy go?" which is good, for this exceeds the limits of the
model.

As soon as one assigns tangible energy to the reflected wave, it
becomes reasonable to ask for an accounting of this energy and
the model is incapable of properly accounting for the energy.

Following this weakness back through the model, the root cause
is the attempt to assign tangible energy to the reflected wave.
Think of it as a reflected voltage or current wave and all will
be well, but assign power to it and eventually incorrect
conclusions will be drawn.

For those who understand this, and know that "where did the
reflected energy go?" is an invalid question, using the power
model within its limits will not cause difficulties. But for
those who are not careful, great difficulties arise and a lot
of fancy dancing is offered to work around the difficulties,
unsuccessfully.

Just for fun, here is a simple example.

100V DC source, connected to a 50 ohm source resistor,
connected to 50 ohm transmission line, connected to a 50 ohm
load resistor. Turn on the source. A voltage step propagates
down the line to the load. The impedances are matched, so
there are no reflections. The source provides 100W. 100W is
dissipated in the source resistor. 100W is dissipated in the
load resistor. Energy moves along the transmission line
from the source to the load at the rate of 50W.
All is well.

Disconnect the load. A voltage step propagates back along
the line from the load to the source. In front of this
step current continues to flow. Behind the step, the
current is 0. When the step reaches the source there is
no longer any current flowing. The source is no longer
providing energy, the source resistor is dissipating
nothing, and neither is the load resistor.

Proponensts of the power model claim that energy is
still flowing down the line, being reflected from the
open end and flowing back to the source. Since the
source is clearly no longer providing energy, great
machinations are required to explain why the reflected
'energy' is re-reflected to provide the forward 'energy'.

But really, does anyone believe that a length of
transmission line, charged to 100V voltage with zero
current flowing, is actually simultaneously transporting
energy in both directions?

For even more fun, replace the ideal conductors in the
transmission line with some lossy conductors. How much
of the reflected and re-reflected energy flowing up and
down the line will be dissipated in the conductors?
Remember that the current is zero, everywhere along
the line.

....Keith