"Walter Maxwell" wrote
Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you
make
this measurement?

==================================

Walt,

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

SWR on the line will be about 1400 and the amount of power available
will not be very great.
----
Reg.

If anyone besides me is having trouble keeping track of what Reg is
trying to say, maybe the following recent quotes will help. That is,
they'll help you understand why you're having trouble keeping track.

For what it's worth, I agree with the first quotation of 8/31. But
apparently Reg doesn't, even though he said it.

Roy Lewallen, W7EL

8/30:

Perhaps somebody might be prepared to state the power actually
radiated from feedlines in watts. At least it may create the
impression you know what you are talking about.

8/30:

Roy, do everybody a favour, by stating, numerically, how much power is
radiated from feedlines. Then somebody might have some confidence in
what you are bafflegabbing about.

8/31:

Any current which finds its way on to (3), which ought to flow in the
antenna, will result in the coax participating in the radiation
pattern of the whole antenna structure.

BUT IT IS A SILLY QUESTION TO ASK HOW MANY WATTS ARE RADIATED FROM THE
FEEDLINE.

OR, CONVERSELY, HOW MANY MICROWATTS ARE PICKED UP BY THE FEEDLINE ON
RECEIVE.

The feedline cannot be treated in isolation as if it behaves
independently of the antenna. For starters, the radiation resistances
of the feedline and antenna do not add arithmetically. They interact
with each other.

8/31:

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

http://www.smeter.net/feeding/feedpowr.php:

Centre-Fed Dipole - Radiation from Coaxial Feedline
Author: R.J.Edwards G4FGQ © 25th March 2003

Program Notes
.. . .
With no loss in accuracy, to simplify the model, the transmitter is
located at the dipole centre and the coaxial line is replaced by a
single conductor of the same diameter as the coaxial braid. There are 3
radiating elements. Radiation resistance, input impedance, and input
current of each element is calculated. Finally, the percent of total
power radiated by each of the three elements is calculated.

Reg Edwards wrote:
If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

I think most RF people would consider radiant heat from the feedline
to be heat dissipation (as opposed to RF radiation).
--
73, Cecil http://www.qsl.net/w5dxp

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Reg, put up the corkscrew, your arguing with yourself. Here, we put people
in rubber rooms that exhibit these propensities...

"Reg Edwards" wrote in message
...

"Walter Maxwell" wrote
Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you
make
this measurement?

==================================

Walt,

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

SWR on the line will be about 1400 and the amount of power available
will not be very great.
----
Reg.

On Thu, 1 Sep 2005 07:35:35 +0000 (UTC), "Reg Edwards"
wrote:


"Walter Maxwell" wrote
Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you
make
this measurement?

==================================

Walt,

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

SWR on the line will be about 1400 and the amount of power available
will not be very great.
----
Reg.

Sorry to disagree, Reg, But if a balun at the feedline-antenna
junction is a perfect balun at 1.9 MHz, NO power will be radiated from
the feedline with any amount of SWR, even 1400. It is true that only
0.1% of the power will be radiated, but the 99.9% will be reflected
back to the input of the line, not radiated,, making a 50-ohm
transmitter see a 1400:1 mismatch. In the steady state the transmitter
will only deliver 0.1% of its available power into the line due to the
mismatch.

The 1400 SWR inside the coax will not cause it to radiate, unless the
outer conductor is full of holes.

Walt

"Walter Maxwell" wrote in message
...
On Thu, 1 Sep 2005 07:35:35 +0000 (UTC), "Reg Edwards"
wrote:


"Walter Maxwell" wrote
Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you
make
this measurement?

==================================

Walt,

If you erect a 10 meter 1/2-wave dipole and center-feed it with a
50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

SWR on the line will be about 1400 and the amount of power
available
will not be very great.
----
Reg.

Sorry to disagree, Reg, But if a balun at the feedline-antenna
junction is a perfect balun at 1.9 MHz, NO power will be radiated
from
the feedline with any amount of SWR, even 1400. It is true that only
0.1% of the power will be radiated, but the 99.9% will be reflected
back to the input of the line, not radiated,, making a 50-ohm
transmitter see a 1400:1 mismatch. In the steady state the
transmitter
will only deliver 0.1% of its available power into the line due to
the
mismatch.

The 1400 SWR inside the coax will not cause it to radiate, unless
the
outer conductor is full of holes.

============================
Walt,

Back along the thread you asked for details of the experiment which
demonstrated that a feedline could radiate as much as 90 percent (of
the available power). But you received no reply.

So I provided an example in which nearly all the power is radiated by
the feedline simply because the short antenna is unable to accept very
much and is inefficient. The power available at the antenna input HAS
to go somewhere if it cannot be accepted by the antenna.

Walt, my statement is correct. There is NO choke balun involved. The
unbalanced coax goes straight into the balanced antenna which
inevitable injects power into the outside of the coax. The choke is
omitted just to acheive that purpose.

I made the statement because you seemed to doubt it was possible for
90 percent of the available power ever to be radiated from an
unbalanced feedline. I may possibly have mis-interpretted you.

Admitted, there may not be very much power available at the antenna
due to high SWR and loss within the coax. But nevertheless most of the
power will be radiated by the outside of the feedline. The feedline
makes an excellent, efficient antenna wire compared with the dipole.

An approximate analysis can possibly be done by using Eznec and
placing the transmitter directly at the center of the dipole.

The outer conductor of the coax can be represented by a thick wire
down to ground, the transmission loss inside the coax being ignored
without having the slightest effect on the experiment.

Incidentally, the length of the feedline in wavelengths and the
resistance of the bottom end ground connection will have a
considerable effect on results.

I mention Eznec because of the number of people who swear by it.

For Roy's benefit, the experiment will not tell him how many watts are
radiated from the feedline because it is impossible to separate the
three radiation resistances involved and there will be only one very
peculiar radiation pattern from their combination.

I entered this extremely long-standing discussion only to say that, in
general, the amount of "Power Radiated from a Feedline" is not worth
the effort which has been expended in waffling about it.

I use the words "Power Radiated from a Feedline" only because, to make
myself understood, I am obliged to use the same confusing language as
used by old-wives for the last 50 years. I try to be helpful.
----
Reg, G4FGQ

Dan wrote:
"We may use this model for a couple of things."

Dan attached a posting from Reg, G4FGQ.

Reg`s description of the "Centre-Fed Dipole - Radiation from Coaxial
Feedline" tells it as it is.

About 45 years ago, I (Richard Harrison) worked for a company exploring
for oil in the Chaco Jungle of Bolivia. Communications were by HF radio
at all sites in the jungle and at offices in Cochabamba and La Paz.
Radios were Collins 30K-5 transmitters and 51-J receivers at all
locations. All antennas were center-fed 1/2-wave dipoles up only about
1/4-wave due to economics and generally were broadside to some favored
direction. The feedline was also about 1/4-wavelength for convenience,
but the antennas loaded, took a lot of power and the 30-K finals dipped
OK. Soil at the radio sites was mostly sand and didn`t really ground
anything very much. The length of the coax presented a high impedance to
the outside shield of the coax cable at the dipole, whatever it might
have been.

At 1/4-wave antenna height, directionality was small and whatever the
coax radiated, it likely filled-in any nulls.

All stations could clearly hear all others all day, so the operators
were satisfied. Much of the radiation was straight up so we likely
bebefitted from near vertical incidence propagation. The transmitters
shook the aether with their power, but the 51-J has a nice dial but not
much else. Nevertheless, everything worked.

My previous employer had given away all its 51-J`s, they were so sorry,
and replaced them with Hammarland SP-600`s. I didn`t take a 51-J, I was
using one of the Super Pro`s.
My experience is anecdotal.

Best regards, Richard Harrison, KB5WZI

Reg, G4FGQ wrote:
"Perhaps somebody might be prepared to state the power actually radiated
from feedlines in watts."

Someone has. A feedline is a way to get energy from here to there.
Usually we want to keep all the energy on or close to the line as it
travels and lose as little as possible to radiation and conversion to
heat.

Terman gives an approximate formula credited to Sterba and Feldman for
radiation from a 2-wire nonresonant line, provided that the lengrh is at
least 20X the spacing and the spacing is less than 0.1 wavelength:

Radiated power/Isquared=160(pi D/lambda)squared.

D/lambda is the spacing in wavelengths

I is the rms line current.

Terman notes that the parallel line radiates 4X the power that a doublet
of length equal to the line spacing would, providing that the line and
doublet currents are equal.

Terman provides a figure to be used to adjust the estimated radiation
upwards for longer feedlines (up to 5 wavelengths), and for greater
heights (up to 0.5 wavelength above the earth).

See 1943 "Radio Engineers` Handbook", page 194.

Best regards, Richard Harrison, KB5WZI

Reg Edwards wrote:
I am truly disappointed with the long-running discourse on balanced
and unbalanced feedlines and the power radiated therefrom. It's been
going on for years.

Nobody, especially poor novices, has ever learned anything from it.

99% of it is bafflegab.

Few of us understand what on Earth is being waffled about. And those
who do, prefer not to waste their time by joining in.

The reason I'm making this seemingly outrageous statement is that
NOBODY HAS EVER QUANTIFIED, not even once, what they are waffling
about. This demonstrates a great ignorance of the subject.

(Remember what Lord Kelvin said about the ability to measure and
quantify what it is you are gabbing about and how that ability is
directly related to what you really know about it.)

Perhaps somebody might be prepared to state the power actually
radiated from feedlines in watts. At least it may create the
impression you know what you are talking about.

It might possibly be at such a low level that, in the great majority
of cases, it's not worth all the megabytes of bandwidth which are
wasted on it.

As an unbiased World Citizen, I now find myself half-way down a bottle
of Merlo, 2000, a produce of France. But I have in reserve some decent
Californian stuff.

May I say how saddened I am to learn about the terrible disastrous
storm which has befallen some of the Southern states.
----
Reg, G4FGQ


Instead of sitting around for years reading the "bafflegab" and then
complaining about it, why didn't you QUANTIFY it yourself and report it so
as to make yourself useful?

John

Roy, W7EL wrote:
"The calculations you qupte assume equal and opposite (i.e. purely
differential mode) currents in the feedline conductors. The topic under
discussion is radiation due to common mode current."

Radiation from current on the outside of a coax feedline can be
calculated too by using formulas appropriate to the actual current
distribution.

Refer to the infamous "ARRL Antenna Book" figure (Fig 24 on page 26-16
of my 19th edition), "showing various current paths at feed point of a
balanced dipole fed eith unbalanced coaxial cable."

From the text:

"The antenna current in arm 2 is thus equal to the difference between I2
and I3.

The magnitude of I3 (on coax exterior) is proportional to the relative
impedance in each current path beyond the split."

Best regards, Richard Harrison, KB5WZI