On Jan 4, 8:58*pm, (Richard Harrison) wrote:
Art wrote:

"-----i.e. his book called "Reflections" which is just a bunch of BS
with respect to what happens at the end of a fractional wave antenna."

Everyone should have access to the 3rd. edition of "Antennas" by Kraus,
Marthelka, and associates. It is a true treasure. On page 177 is found
Figure 6-7, Approximate natural-current distribution for thin, linear,
center-fed antennas of various lengths.`

In each case, at the open-circuit end current drops to near zero. No
surprise, as Terman says on page 866 of his 1955 opus:
"Under most circumstances the losses are sufficiently low and the ratio
of wire length to diameter sufficiently great so that to a first
approximation the current distribution can be taken as that for a line
with zero losses; it then has the characteristics discussed in Sec.
4-5."

Section 4-5 is titled: "The Effect of Attenuation on Voltage and Current
Distribution".

Point is that antennas share current distribution characteristics with
transmission lines, and Sec. 4-5 is in Terman`s Chapter 4 (Transmission
Lines). This chapter starts on page 82 of "Electronic And Radio
Engineering" from that wonderful year 1955. The transmission line
chapter shows in excellent detail how incident and reflected waves
combine, and the energy patterns produced on antennas as well as on
lines. * *

Walter Maxwell is in-step with Terman and Kraus.

Best regards, Richard Harrison, KB5WZI

What does it take for you to understand that I am NOT in agreement
with the books?
Your lemmings aproach that if it is printed in a book it must be true
is just not my style.
'I see no discontinuety at the ends of the antenna so the law on
discontinuity does not apply..
I do see a discontinuity in a transmission line so the laws on
discontinuity do apply..
As in the past I have stated why I am not in agreement with the books
as I cannot justify it via first principles.
I have asked for input as to what the discontinuity is that creates a
reflection which requires the application of the law.
nobody has explaned to my satisfaction the position taken by the
books. My suspicion is that idea of discontinuity was assigned prior
to the Foucault discovery when the pertinent facts were unknown tho I
do suspect some residences are wired with an open circuit in lines to
save wire and thus costs required for a closed circuit
Grin

On Jan 4, 10:55 am, Richard Clark wrote:
In recent correspondence we have been regaled with the possibilities,
the probabilities, the certainties that some fastidious, and
well-heeled Ham "could" achieve the determination of RF power to
within 0.1dB of its actual value.

At HF and VHF, you should be able to do power measurements to a tenth of
a dB, with moderate care.

1. That budget (with an ironic eye towards the language's claim of
"moderate") is a generous $1000 - with that budget being invested
solely towards the measurement (and not in the capital equipment of
transmitter and antenna) through the costs of ancillary equipment
acquisition and of guarantees of absolute accuracy as further
described below.

2. That frequency is 14.1MHz.

3. That power is 10mW.

4. That application is measuring the full power applied from a 100W
rated Ham grade transmitter/transceiver directly (or through a
directional coupler) to
a. an unloaded quarterwave thin antenna sited over 120 half-wave
radials placed slightly above, upon, or slightly below the ground
(slightly being defined as that recommended by an NEC modeling tool
for ground radial modeling); or
b. an unloaded halfwave thin antenna sited in free space.

5. That fully expressed tolerances for all components, capital and
ancillary equipment involved where the budget also absorbs their cost
of determination of their contribution to error.

6. That fully expressed tolerances for sources of system error.

7. That outcome of accuracy of power determination being applied to
the nominal 100W of power at the load and not the nominal 10mW of
power to the sensor.

* * * * * * * *

This will be a very short thread devoid of conclusion when the
poster(s) suddenly become aware of the expense exceeding the budget.
For those who challenge this artificial budgetary limitation, try
asking Congress for a bailout.

73's
Richard Clark, KB7QHC


No problem. Send money. This is, after all, something I do for a
living. I assume, of course, that your $1000 budget assumes labor is
free? (the usual situation for ham measurements)

As you are well aware, most of the cost of accurate (and perhaps
precise) measurements that are calibrated is not in the equipment, but
in the knowledge and effort in making the measurement and doing the
uncertainty analysis to prove that what you say is the measurement is
within some known distance of the measurand. After all, one could beat
your $1000 budget by saying that you should start with sand and iron
ore, and invest copious effort in smelting, refining, machining,
etc... Certainly, the cost of preparing the uncertainty analysis is
low, being paper and pencil, aside from the labor. The books sold by
Lindsay Books might be an example of how one can start with scrap
metal, and wind up with a machine shop, albeit at the investment of
substantial time.

If one has to pay for the skilled labor, either directly, or
indirectly by buying a piece of equipment designed, manufactured, or
calibrated by someone else, it's another thing entirely, eh?

I will concede that there is a catch.. if one is investing one's free
labor, it is conceivable that the time required to start from first
principles and raw materials would be long enough that your standards
or equipment would drift enough to prevent achieving the measurement
accuracy needed. It's the "you can't use a striped snake as a scale/
ruler, because it keeps moving and growing" problem.

However, from an academic perspective, your challenge is interesting.
It would be interesting to see a decent article in QST or QEX that
would describe readily achievable measurement accuracies for hams (and
do away with that horrible term you see in ads and equipment reviews:
"lab-grade"). Interesting, but not as interesting as other things I
might spend my free time on.

Jim, W6RMK

On Sun, 04 Jan 2009 10:55:21 -0800, Richard Clark
wrote:

well-heeled Ham "could" achieve the determination of RF power to
within 0.1dB of its actual value.

RF power at 14.1MHz or including all the spurs and harmonics that come
with it? They're probably not much of an issue with the typical ham
100watt xmitter, but certainly are a problem with QRP hardware that
sometimes has no output LPF of any kind.

Also, do you want the 50 ohm terminated RF power, or measured through
the line to a random antenna load?

3. That power is 10mW.

0.1dB is about 2.3% accuracy. Plenty of lab grade hardware around,
but none with 10mw full scale sensor:
http://www.bird-electronic.com/products/subcategory.aspx?sid=79

However, with a $1000 prize, I guess something cheaper will be
required. How about a:
http://www.ohr.com/wattmeter.htm
Not anywhere near as accurate as you want, but for a single 14.1Mhz
frequency, I would have no problem using a properly calibrated signal
generator to create a calibration chart. Also, some environmental
isolation and a temperature compensation chart will be useful.

Ummm..... why do you need such accuracy? Is there some kind of QRP
ultra low power contest that I don't know about? Amateur metrology?

Send the $1000 to the address below.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Richard Harrison wrote:
Point is that antennas share current distribution characteristics with
transmission lines, ...

Here is a transmission line simulation of half of a
dipole in free space. The resistivity of the wire has
been adjusted to simulate radiation loss resulting in
a feedpoint impedance of 35 ohms.

http://www.w5dxp.com/stub_dip.EZ

If the line is terminated in its Z0 impedance of
approximately 620 ohms, the current distribution
clearly shows the forward current including phase
shift.
--
73, Cecil http://www.w5dxp.com

Art Unwin wrote:
'I see no discontinuety at the ends of the antenna so the law on
discontinuity does not apply..
I do see a discontinuity in a transmission line so the laws on
discontinuity do apply..

A #14 horizontal wire 30 feet above ground is a "single-
wire above-ground transmission line" line with a
Z0 = 138*log(4D/d) = 600 ohms where 'd' is the diameter
of the wire and 'D' is the height above ground. The ground
is the other half of the transmission line.
--
73, Cecil http://www.w5dxp.com

On Jan 5, 6:24*am, Cecil Moore wrote:
Art Unwin wrote:
'I see no discontinuety at the ends of the antenna so the *law on
discontinuity does not apply..
I do see a discontinuity in a transmission line so the laws on
discontinuity do apply..

A #14 horizontal wire 30 feet above ground is a "single-
wire above-ground transmission line" line with a
Z0 = 138*log(4D/d) = 600 ohms where 'd' is the diameter
of the wire and 'D' is the height above ground. The ground
is the other half of the transmission line.
--
73, Cecil *http://www.w5dxp.com

Common aurgument revolve about accounterbility for surrounding
fields. Your " transmission line" is hardly a conventional one to use
in such auguements
But then again my abilities in this area are not sufficient for
auguement or debate which is why I ask questions
Best regards
Art

On Sun, 4 Jan 2009 21:26:18 -0800 (PST), wrote:

After all, one could beat
your $1000 budget by saying that you should start with sand and iron
ore, and invest copious effort in smelting, refining, machining,
etc... Certainly, the cost of preparing the uncertainty analysis is
low, being paper and pencil, aside from the labor. The books sold by
Lindsay Books might be an example of how one can start with scrap
metal, and wind up with a machine shop, albeit at the investment of
substantial time.

Well Jim,

"Beating" the budget is a strange progression toward tackling a
problem, couched in sentimentality worthy of "Tess of the
D'Urbervilles."

Half that budget could buy the RF Head to the HP 8902 measuring
receiver. In my various standards labs, we would rent it for a month
at 1/10th the cost. $50 and fully traceable with an equivalent of
$9500 acquisition potential available from a budget barely nicked. If
you prefer to build it up from components of sand and iron, an abject
collapse of alternative solutions, then the remaining budget has no
utility. The defeatism of "sand and iron ore" capped that off
majestically.

I well anticipated that putting a budget to this would cast a pall of
failure if this problem's solution were cut off from infinite
resource. I'm amused it came with the sallowness of antiquity.

On Sun, 4 Jan 2009 21:39:12 -0800 (PST), wrote:
I'm not
about to go dragging out data sheets and doing an uncertainty analysis
which is of very little value to me, personally, and realistically, of
little value to anyone on this list.

I would tend to agree that technology, accuracy, scientific method,
measurement, and bench work have very little to do with the parade of
ego that passes as correspondence here. Typically, lurkers and those
put off by this lack of substance in response to their postings here
approach me through email for technical resolution.

However, I am happy to accord to the recreational purpose in posting
to the group. Many have expressed value in my own poesy. I am
willing to admit that value runs both positive and negative - Art
would strangle on his spit if he didn't have a target. ;-)

73's
Richard Clark, KB7QHC

On Sun, 04 Jan 2009 22:30:27 -0800, Jeff Liebermann
wrote:

On Sun, 04 Jan 2009 10:55:21 -0800, Richard Clark
wrote:

well-heeled Ham "could" achieve the determination of RF power to
within 0.1dB of its actual value.

RF power at 14.1MHz or including all the spurs and harmonics that come
with it? They're probably not much of an issue with the typical ham
100watt xmitter, but certainly are a problem with QRP hardware that
sometimes has no output LPF of any kind.

Hi Jeff,

Power is heat in this particular scenario. All forms of heat
contribution lend to error. The specification (in part):
4. That application is measuring the full power applied from a 100W
rated Ham grade transmitter/transceiver
is sufficient and necessary for the challenge's purposes.

Also, do you want the 50 ohm terminated RF power, or measured through
the line to a random antenna load?
7. That outcome of accuracy of power determination being applied to
the nominal 100W of power at the load and not the nominal 10mW of
power to the sensor.

Consult the complete part 4 specification for alternatives in the
load.

3. That power is 10mW.

0.1dB is about 2.3% accuracy. Plenty of lab grade hardware around,

That is why I selected that power level. An instrument does not
encompass a system, however.

but none with 10mw full scale sensor:
http://www.bird-electronic.com/products/subcategory.aspx?sid=79

None? And this is in the same span of a paragraph regaling the
commonplace accessibility of lab grade hardware? I now have to ask
what kind of lab are you thinking of?

However, with a $1000 prize,

Prize? Was the posting so long as for the purpose of $1000 to become
so aggrandized?

I guess something cheaper will be
required. How about a:
http://www.ohr.com/wattmeter.htm
Not anywhere near as accurate as you want, but for a single 14.1Mhz
frequency, I would have no problem using a properly calibrated signal
generator to create a calibration chart. Also, some environmental
isolation and a temperature compensation chart will be useful.

Accuracy is in the calibration. I have calibrated some pretty rough
looking gear to accuracies that better commercial equipment. The
specification was purposely tailored for Amateur application, to the
least constraint, to the maximum of accuracy, for the cheapest cost.

Ummm..... why do you need such accuracy?

I don't.

Is there some kind of QRP
ultra low power contest that I don't know about?

Possibly. There are a multitude of activities you may be unaware of,
and I would be the last to know.

Amateur metrology?

Yes, a conceptual strain apparently. In this age where the closest a
Ham gets to technology is pushing a credit card across the display
case for a new toy, this has proven to be asking for too much.

Send the $1000 to the address below.

Send it for what? Do I sign as Treasury Secretary Paulson?

73's
Richard Clark, KB7QHC