"Richard Clark" wrote in message
...
On Sun, 4 Nov 2007 22:10:19 -0700, "Sal M. Onella"
wrote:


"Owen Duffy" wrote in message
...
"Sal M. Onella" wrote in
:

as heat somewhere in the system. If too much is reflected back from
the antenna and dissipated within in your transmitter, the
transmitter
overheats ($$$) or it reduces power to protect itself and nobody
hears
you.

Here we go again!

Owen

What did I say wrong?

You offered only half the evidence, as in the following instance:

On Sun, 4 Nov 2007 22:30:30 -0700, "Sal M. Onella"
wrote:


"Cecil Moore" wrote in message
news
Roy Lewallen wrote:
Yes, this misconception will never die. Is it really worth the
trouble
continually trying to contradict it?

Not if all you do is trade one old-wives tale
for another.

It's hardly an old wives' tale.

I mistakenly put a 2m antenna on my dual band HT and tried to use it for
a
short QSO on a nearby 440 repeater. The other ham said I was barely
making
the repeater, while my poor HT got so hot that I could barely hold it
after
a minute's use.

The antenna was wrong and the heat was real -- whatever the theory behind
it.

In the explanations that hammered you for your naivete, there was no
support of what was obvious to you, and perfectly acceptable as a true
portion of a complete description. You testified to the experience of
observing more heat where odds would have had you as likely testifying
to the experience of observing less heat. We get none of those "less
heat" reports because they naturally go unobserved. This is simply
the common response to a psychomotor lesson instructed from Mom who I
am sure warned you to "never stick your hand in the oven" but probably
never uttered "never stick your hand in the ice-box." The first bears
warning for its obvious consequences, the second hardly demands
mentioning where its consequence is far less dramatic.

So we have these dramas over heat and the stage is filled with tenors
crying their lungs out about the evils of misunderstandings (the last
act of "Romeo and Juliet" comes to mind).

We should also first establish that your HT also exhibits waste heat.
As no common transmitter of notable power is 100% efficient, it is
raising its heat content in relation to its surroundings. If your
hand temperature is cooler than that case surface, you note heating;
contrariwise, if your hand temperature is warmer than that surface,
you note cooling. As almost every item within reach of you is at room
temperature and you rarely note it as cooler, it is hardly worth
mentioning.

Your's was a sin of omission and what "you said wrong" was more in
that neglect of mentioning all the cooling experiences in your life
when your HT was mismatched. Of all the web pages, treatises, papers,
tomes, chapters and verses dedicated to eradicating the myth of
reflected power, all of them are equally sinful in their omissions.
You are not alone there in Reflected Power Hell.

Let's begin first with "reflected power." It is in fact reflected
energy that is noteworthy here, power is merely the manifestation of
energy at a load. With this discussion of the HT and an antenna,
there are two loads (and this raises the tenor's volume of agony
another octave - I will leave that Operetta for other discussion).

The HT as a load is already exhibiting waste heat. Everyone's
experience of operating one for several minutes will testify to that
(yes, more anecdotal evidence) even when it is pushing energy into a
matched load. Let's take the experience of your mismatch and put that
antenna on a variable transmission line (one of those bench top tools,
aka the "Sliding Load," few here have had experience with) and run the
line through 360° of variation as noted at the source (your HT). This
study will fill in all those omissions from those publications so
cleverly painted up and distributed across the web as sage advice.

When that returned energy meets the source energy and combines at the
source, there are 360° of variation possible outcomes. This
combination can be in series aiding, in series opposition, or in all
points in between. This will be a function of the length of the
variable line. You add two aiding energies to the same load and it
will raise its temperature against waste heat. You add two opposing
energies to the same load and it will subdue its temperature against
waste heat. These are the extreme outcomes that fall 180° apart based
on the length of that variable transmission line. One outcome burns
your hand, as you've already noted, the other does not (and you
neglected to inform us of all those occasions you naughty boy!). All
the combinations in between were by relation, inconsequential, and
passed unnoticed (even more sins of omission).

Hence, the problem of anecdotal evidence is that it does not report
fully. However, applying the label "anecdotal" does not automatically
invalidate the observer's credible but isolated reporting; it merely
demands a fuller examination. Unfortunately, you were denied this
full examination in the criticism of your true observation. You
observed one data point and perhaps were guilty of expanding it to
describe a general condition = reflected power always heats a source.
In fact, reflected energy can heat or cool a source in relation to its
existing waste heat. The degree of heating or cooling is found in the
magnitude of the mismatch, and the number of degrees that separate the
load and the source.

As for all the side comments about how "reflections" do not contain
(fill in the blank) ______; and that these issues are instead answered
by Impedance relationships instead - Baloney cut thick. Reflections
AND Impedance relationships occupy opposite sides of the same coin and
are equally applicable. This concept of mutuality is so ingrained in
the catechism of RF as to taint anyone who denies one explanation for
the sake of the other as evidence of some special circumstance. In
this regard, you were sinned against in kind. ;-)

73's
Richard Clark, KB7QHC

So, when you were on staff at USN ET "A" School, where we both taught, did
you know better than the "reflected power" legend/old-wives-tale/heresy?
Hell, that's where I first picked it up !!!!!!!!!!!!!!!

John

On Mon, 5 Nov 2007 17:30:26 -0800, "Sal M. Onella"
wrote:

So, when you were on staff at USN ET "A" School, where we both taught, did
you know better than the "reflected power" legend/old-wives-tale/heresy?
Hell, that's where I first picked it up !!!!!!!!!!!!!!!

Hi John,

My path up through "A" school was through the Radar branch (I was the
only ETR2 in the Communications Branch when I taught there). The
Radar training gave us hands on experience with equipment that
presented both lumped (pulse forming network) AND line (Magic T and
such) designs. Also, reflected POWER was palpably lethal in both
applications. Melodramatic criticism of the fine points in
terminology carried little weight in lab exercises.

Luckily, I had the presence of mind as a student to hie myself into
Frisco to buy Terman's "Electronic and Radio Engineering." The Navy
course of instruction and training manuals so perfectly dove-tailed to
that book that the fit was a precision match. The "A" school syllabus
didn't go nearly to the depth of detail as offered by Terman (the
ET1&2 and ETC course work did), but it did heavily touch every chapter
found in that tome.

Insofar as heresy, the syllabus was rife with it. We taught that
antennas that were too short could be made to appear longer by the
addition of the "missing" wire in the form of a coil. Similarly, a
too long antenna could be reduced in length by inserting a capacitor.
The teaching aid was to think of the coil symbol as a spring that
could be stretched to lengthen the short antenna, and cap symbol as
providing space enough between the plates to collapse the extra length
of a too long antenna. Clearly the metaphors wheeze, but are
effective well beyond mathematical proofs that could only serve as
sleeping pills.

Before the purists roll their eye's and mutter "tut-tut" under their
beards - instruction was complete to point out these were short-cuts
as memory aides and did not serve as a complete discussion on the
topic. Reflected power certainly fell into that category as its
hazard was positively destructive and not a mental exercise subjected
to debate in a perfumed symposium.

Anyone with radar experience can fashion the plumbing to steer
reflected power to any load. -um- reflected energy be damned at that
point as any reflection was inherently returning to a source that was
long dormant (in terms of microseconds) and ready to dissipate
anything that came down the pipe. The whole point of the magnetron's
success in war was its robustness in the face of catastrophic
mismatches. The PFN might flame out or the thyratron burst, but the
magnetron would survive.

73's
Richard Clark, KB7QHC

The whole point of the magnetron's
success in war was its robustness in the face of catastrophic
mismatches. The PFN might flame out or the thyratron burst, but the
magnetron would survive.

A good thing too, or we would all be eating cold leftovers without
that magic 'radar range'...
Jeez, I still have the original Frigidaire that I bought in the late
60's when I worked for GM - got an employees special deal just in time
for xmas, the first family in our neighborhood to have a radar range,
the neighbors marveled... The kids whipped that puppy day and night...
It has outlived three houses... It has been relegated to my R&D shop
where it happily heats epoxy, paint, putty, and cups of tea with
aplomb... I cannot even begin to guess how many tens of thousands of
times it has been cycled... Dozens of times a day for a quarter
century when the kids were still home...

denny / k8do

On Tue, 06 Nov 2007 04:32:37 -0800, Denny wrote:

The whole point of the magnetron's
success in war was its robustness in the face of catastrophic
mismatches. The PFN might flame out or the thyratron burst, but the
magnetron would survive.

A good thing too, or we would all be eating cold leftovers without
that magic 'radar range'...
Jeez, I still have the original Frigidaire that I bought in the late
60's when I worked for GM - got an employees special deal just in time
for xmas, the first family in our neighborhood to have a radar range,
the neighbors marveled... The kids whipped that puppy day and night...
It has outlived three houses... It has been relegated to my R&D shop
where it happily heats epoxy, paint, putty, and cups of tea with
aplomb... I cannot even begin to guess how many tens of thousands of
times it has been cycled... Dozens of times a day for a quarter
century when the kids were still home...

denny / k8do

Hi All,

May I come in with some comments from a somewhat different perspective concerning where the reflected power
goes, or where it doesn't go?

Because I'm not particularly adept concerning solid-state tx, this discussion will involve only tube tx with
pi-network output circuits. We'll assume that when the tx has been adjusted to deliver all its available power
into a resistive load, the output resistance appearing at the output terminals of the tx is equal to the load
resistance. For those who may disagree I refer them either to Chapter 19 in Reflections 2, or the May/Jun
issue of QEX, where I report the results of measurements that prove the statement to be true.

Consequently, we'll begin by adjusting the tx to deliver all its available power into a 50-ohm resistive load,
a real 50-ohm physical resistor. Next, we'll change the load to be the input of a 50-ohm lossless transmission
line terminated with a 3:1 mismatched load. What impedance will the tx see? Until we specify the actual load
terminating the line and the electrical length of the line, the tx may see any impedance appearing somewhere
on the 3:1 SWR circle of the Smith Chart. What will happen when the tx sees this mismatched load? First,
because the 3:1 SWR results from a voltage reflection coefficient of magnitude rho of 0.5 (and a power
reflection coefficient of 0.25), this mismatch will cause the tx to reduce its output to deliver only 75
percent of the power delivered into the matched 50-ohm load.

Will the reflected power enter the tx and cause heating? Or will it cause cooling? The answer is that the
reflected power does not enter the tx. So what does happen?

By changing the length of the transmission line at will, we can cause any impedance found on the 3:1 SWR
circle on the Smith Chart to appear at the input terminals of the line. Let's assume the impedance found there
is 50 ohms x 3 equals 150 ohms. This impedance is a lighter load than the original 50-ohm load, so the plate
current will be less than with the 50-ohm load. However, the reflected power did not enter the tx, it only
caused the 150 plus j0.0-ohm impedance to appear at the line input.

Now the important point: The tx would have responded in exactly the same manner if its new load had been a
physical resistor of 150 ohms instead of a 'virtual' resistance of 150 ohms resulting from voltage/current
relationship appearing at the input of the line.

Let's now consider if the line-input impedance is 50/3 ohms, which equals 16.667 ohms. In this case the new
load is lower than the original 50-ohm load, resulting in overloading the tx, causing the plate current to
rise above the rated level, thus causing overheating. But the overheating was caused only by the increase in
plate current resulting from the lowered load resistance, not by reflected power entering the tx. Again, the
same condition would have occurred if a physical resistor of 16.667 ohms had loaded the tx instead of the same
value of virtual resistance appearing at the line input.

Now a third case important to the issue, that in which the impedance appearing at the line input is 50 plus
j57.738 ohms, which also appears on the 3:1 SWR circle. In this case the 57.738 ohms of inductance simply
detunes the pi-network away from resonance, causing plate current to rise, increasing the temperature, but
still reducing the output power to 75 percent of that with the 50-ohm load. And again, precisely the same
result would occur if the new load had been a physical resistance of 50 ohms in series with a physical
57.738-ohm inductor. (It should be obvious that a simple readjustment of the plate capacitor of the pi-network
would return the network to resonance, with the result that the operation of the tx would be identical to that
when loaded with the 50-ohm physical resistor.

The purpose of this commentary is to show that reflected power does not enter the tx, and that the tx cannot
distinguish between a 'virtual' load impedance appearing at the input of a mismatched transmission line and a
physical load comprising a resistor in series with an inductor-the results will be identical in either case.

Walt, W2DU

On 7 Nov, 14:30, Walter Maxwell wrote:
On Tue, 06 Nov 2007 04:32:37 -0800, Denny wrote:
The whole point of the magnetron's
success in war was its robustness in the face of catastrophic
mismatches. The PFN might flame out or the thyratron burst, but the
magnetron would survive.

A good thing too, or we would all be eating cold leftovers without
that magic 'radar range'...
Jeez, I still have the original Frigidaire that I bought in the late
60's when I worked for GM - got an employees special deal just in time
for xmas, the first family in our neighborhood to have a radar range,
the neighbors marveled... The kids whipped that puppy day and night...
It has outlived three houses... It has been relegated to my R&D shop
where it happily heats epoxy, paint, putty, and cups of tea with
aplomb... I cannot even begin to guess how many tens of thousands of
times it has been cycled... Dozens of times a day for a quarter
century when the kids were still home...

denny / k8do

Hi All,

May I come in with some comments from a somewhat different perspective concerning where the reflected power
goes, or where it doesn't go?

Because I'm not particularly adept concerning solid-state tx, this discussion will involve only tube tx with
pi-network output circuits. We'll assume that when the tx has been adjusted to deliver all its available power
into a resistive load, the output resistance appearing at the output terminals of the tx is equal to the load
resistance. For those who may disagree I refer them either to Chapter 19 in Reflections 2, or the May/Jun
issue of QEX, where I report the results of measurements that prove the statement to be true.

Consequently, we'll begin by adjusting the tx to deliver all its available power into a 50-ohm resistive load,
a real 50-ohm physical resistor. Next, we'll change the load to be the input of a 50-ohm lossless transmission
line terminated with a 3:1 mismatched load. What impedance will the tx see? Until we specify the actual load
terminating the line and the electrical length of the line, the tx may see any impedance appearing somewhere
on the 3:1 SWR circle of the Smith Chart. What will happen when the tx sees this mismatched load? First,
because the 3:1 SWR results from a voltage reflection coefficient of magnitude rho of 0.5 (and a power
reflection coefficient of 0.25), this mismatch will cause the tx to reduce its output to deliver only 75
percent of the power delivered into the matched 50-ohm load.

Will the reflected power enter the tx and cause heating? Or will it cause cooling? The answer is that the
reflected power does not enter the tx. So what does happen?

By changing the length of the transmission line at will, we can cause any impedance found on the 3:1 SWR
circle on the Smith Chart to appear at the input terminals of the line. Let's assume the impedance found there
is 50 ohms x 3 equals 150 ohms. This impedance is a lighter load than the original 50-ohm load, so the plate
current will be less than with the 50-ohm load. However, the reflected power did not enter the tx, it only
caused the 150 plus j0.0-ohm impedance to appear at the line input.

Now the important point: The tx would have responded in exactly the same manner if its new load had been a
physical resistor of 150 ohms instead of a 'virtual' resistance of 150 ohms resulting from voltage/current
relationship appearing at the input of the line.

Let's now consider if the line-input impedance is 50/3 ohms, which equals 16.667 ohms. In this case the new
load is lower than the original 50-ohm load, resulting in overloading the tx, causing the plate current to
rise above the rated level, thus causing overheating. But the overheating was caused only by the increase in
plate current resulting from the lowered load resistance, not by reflected power entering the tx. Again, the
same condition would have occurred if a physical resistor of 16.667 ohms had loaded the tx instead of the same
value of virtual resistance appearing at the line input.

Now a third case important to the issue, that in which the impedance appearing at the line input is 50 plus
j57.738 ohms, which also appears on the 3:1 SWR circle. In this case the 57.738 ohms of inductance simply
detunes the pi-network away from resonance, causing plate current to rise, increasing the temperature, but
still reducing the output power to 75 percent of that with the 50-ohm load. And again, precisely the same
result would occur if the new load had been a physical resistance of 50 ohms in series with a physical
57.738-ohm inductor. (It should be obvious that a simple readjustment of the plate capacitor of the pi-network
would return the network to resonance, with the result that the operation of the tx would be identical to that
when loaded with the 50-ohm physical resistor.

The purpose of this commentary is to show that reflected power does not enter the tx, and that the tx cannot
distinguish between a 'virtual' load impedance appearing at the input of a mismatched transmission line and a
physical load comprising a resistor in series with an inductor-the results will be identical in either case.

Walt, W2DU- Hide quoted text -

- Show quoted text -

Oh my.All this discussion to help out a newby. So many differences, so
many arguments
it is enough to push a newby away from ham radio.
Let's keep it simple.An antenna is just a pendulum with two energy
storage tanks per cycle.
Each energy tank releases the same amount of energy for the other
energy tank to catch and store before he sends it back.
They call these energy tanks distributed capacitance and inductance
and they are only equal in size
at one wavelength.Anything different from a wavelength and one side
releases more energy
than the other side so you must come to the aid of one side or live
with the consequences of imbalance
which is measured by SWSR, that is the pendulum swings more one way
than the other.
Now you have two energy sources throwing energy at each other ,harder
and harder
such that the transmitter or the onlooking manager starts to get all
sweaty and close to a heart attack.
If the energy sources want to stay on the team and the manager doesn't
want a heart attack then every body shuts down until they find a way
for the pendulum to swing smoothly backwards and forwards in a
friendly manner.
See, antennas are not all that hard to understand if you have the time
to do things right. Forget about photons and reflections which
everybody is arguing about, just make sure that your antenna and
transmitter is happy by keeping the swr down as it is this that
disturbs the operation and nothing more.
Art

Art wrote:
"Let`s keep it simple. An antenna is just a pendulum with two energy
storage tanks per cycle."

Not too late for a truth squad to clean up the above, I hope.

I infer from the above that Art implies an antenna to be a resonant
circuit. Many are resonant because a resonant antenna has no net
reactance to impede the signal.

But, there is a non-resonant class of antennas. Antennas in this class
often have radiating conductors terminated at their far ends in their
characteristic resistances (Ro). Traveling waves, reaching Ro which have
not yet been radiated are simply absorbed. There is no reflection and no
standing waves. Up to 50% of the energy fed to the antenna may be wasted
but usually it is somewhat less.

50% waste is a lot, but the directive gain of a typical rhombic may be
50 times according to Fig. 23-18 on page 882 of Terman`s 1955 opus. I`ve
used ountless rhombics and attest that Terman got it right.

Point is, there`s no pendulum up there, only simple wires carrying RF
and they radiate like gangbusters!

Best regards, Richard Harrison, KB5WZI