On Fri, 05 Nov 2004 07:45:16 GMT, Richard Clark
wrote:
First I will start with a conventionally sized quarterwave and by
iteration approach the short antenna and observe effects. I am using
the model VERT1.EZ that is in the EZNEC distribution and modifying it
by turns. For instance, I immediately turn on the wire loss.

For this progression, I have amended the design through the addition
of 1 wire, 20M long, 21 segments, Vertically polarized, center loaded
with a 73 Ohm Resistor, 4000M remote from the test antenna, and
elevated 2127M to sample the radiation lobe at an angle of 27° which
represents the Best gain angle from previous results (or nearly so).

I further perform readings of the 73 Ohm load under two conditions of
the test antenna. Those conditions are when it is excited by 1A (the
constant current mode) and when it is excited by 36.65W (the constant
power mode). I also include the power into the antenna for the
constant current mode.

40mm thick radiator 10.3 meters tall:
Impedance = 36.68 + J 2.999 ohms
Best gain is
-0.03dBi
Power = 4.214E-05 watts for 1 A excitation
Power = 4.214E-05 watts for 36.65W

next iteration:
cut that sucker in half:
Impedance = 6.867 - J 301 ohms
best gain
0.16dBi
Power = 7.979E-06 watts for 1A excitation
Total applied power = 6.856 watts for 1A excitation
Power = 4.266E-05 watts for 36.65W excitation

next iteration:
load that sucker for grins and giggles:
load = 605 Ohms Xl up 55%
Impedance = 13.43 + J 0.1587 ohms
best gain
0.13dBi
Power = 1.559E-05 watts for 1A excitation
Total applied power = 13.41 watts for 1A excitation
Power = 4.262E-05 watts for 36.65W excitation

next iteration:
cut that sucker down half again (and remove the load):
Impedance = 1.59 - J 624.6 ohms
best gain:
0.25dBi
Power = 1.849E-06 watts for 1A excitation
Total applied power = 1.585 watts for 1A excitation
Power = 4.274E-05 watts for 36.65W excitation

next iteration:
load = 1220 Ohms Xl up 55%
Impedance = 3.791 + J 1.232 ohms
best gain:
0.23dBi
Power = 4.407E-06 watts for 1A excitation
Total applied power = 3.78 watts for 1A excitation
Power = 4.272E-05 watts for 36.65W excitation

Now, all of this is for a source that is a constant current generator;
we've monkeyed with the current distribution and put more resistance
(Rr?) into the equation with loading; and each time loading craps in
the punch bowl.

So much for theories of Rr being modified by loading. I would
appreciate other effort in kind to correct any oversights I've made
(not just the usual palaver of tedious "explanations" - especially
those sophmoric studies of current-in/current-out).

Well, now we can review this data in light of my previous
editorializations.

We begin with the premise that Rr is evidenced by the power expressed
by a known current through an unknown (Rr) resistance. We needn't
concern ourselves with the constant power mode as it closely mimics
the former data. In essence, it serves as a validation of the two
models (the previous post and this post).

However, the constant current mode does show a variation in power
received at the sniffer antenna. For a shorter antenna, there is a
corresponding fall in the power. Counter to my editorial observations
above there is an increase in this power received at the sniffer
antenna when a load is applied. The contrast in my former editorial
observation and this data reveals that Yes the Rr is impacted by
loading and that the drivepoint Z is the Rr.

This comes as no surprise to many.

Now, let us return to a point of analytical bias that lead me to
believe no apparent change in Rr was observable. In fact there was no
way to make it observable except through the artifice of my sniffer
antenna. For the model of the constant current generator, it is a
truism that gain (that is true gain for a system and not simply
antenna directivity) must increase for the same excitation. After
all, we are changing the Rr either through the actuality of modified
length, or the artifice of a moving, variable load along the short
radiator. Such gain is only observable through a circuit (broadcaster
lingo for a transmit/receive pair).

In the back of my mind I was troubled about comparing situations in
dBi. Yesterday I expressed this as a possible source of confusion for
the effects sought in evidence against the obvious gain differential.
dBi is a dimensionless relation such that true gain is washed out of
the result. When I attempted to confirm my suspicions through field
expressions of mv/M for 1KW, I was struck that that too forced the
results to a constant power (not constant current) and thus hid the
gain demonstration in the same way. I then fell back on my practice
of employing a sniffer antenna to test reality and the data is found
above confirming the gain that would be expected. In other words, the
far field's power followed the diminution of Rr with a positive
correlation. It also followed the subsequent increase of Rr (with a
load applied to that shortened radiator) with a positive correlation.

73's
Richard Clark, KB7QHC

Thanks for the info, have downloaded the demo program. Have heard about it
from many sources, so have wanted to experiment with the program for some
time. I am more familiar with the basic NEC code, and have been using it
for years.

Regards,

Frank


"Roy Lewallen" wrote in message
...
Frank wrote:
Now I understand the confusion. I am not using EZNEC, and am not
familiar with the program. . .

You can download a free demo version of EZNEC from http://eznec.com. It's
perfectly adequate for analysis of simple antennas with lumped loads, and
gives you full graphics, the ability to fix the power level, and all the
other features of the full EZNEC program with the single exception of a 20
segment limit.

The demo version also includes the full EZNEC/EZNEC+/EZNEC pro manual, and
there's no time limit on its use.

Roy Lewallen, W7EL

Yuri Blanarovich wrote:

Rattlesnakes shouldn't mind being killed, since, after they die,
they're immediately reincarnated as Republicans. Come to think of
it,though,
maybe they should mind after all.
73,
Tom Donaly, KA6RUH



That says it all!

Cecil, you are arguing with brainwashed liberals. I escaped from that crap, but
it haunts me here, even on the radio internet waves.

Viva Bush!

Yuri da BUm

I'd like to apologize for that statement. If I offended any
good, God-fearing, American rattlesnakes by that post, I'd
like them to know that I'm sorry and it won't happen again.
There are some things that are just too low to compare anything
to.
73,
Tom Donaly, KA6RUH

On Fri, 05 Nov 2004 18:51:01 -0700, Wes Stewart
wrote:
I believe it is your contention that loading to resonance with an
arbitrarily positioned inductor, or not loading at all, does not
affect the gain, and the radiation resistance is not the same as the
changing feedpoint resistance.

Hi Wes,

You show a unique power of observation. English is difficult for many
here.

I am in the other camp, along with Hansen, Devoldere, et. al. who say
that the current distribution does affect the radiation resistance
(and in the real world, the gain/efficiency).

You may have observed of late that recent a posting by me confirms
your understanding.

I hope you would agree that the normalized gain would be a good proxy
for efficiency.

I think "normalization" is were things went awry.

For example if we use the lossless 1/4 wavelength monopole over
perfect ground as a reference, then gain with respect to that (5.15
dBi) would be an indicator of efficiency.

I believe that you will agree that the efficiency can be determined
by:

Rr
eta = ------------- Eq.1
Rr + Rg + Rl

where Rr = radiation resistance
Rg = ground resistance
Rl = all other resistances (conductor, etc)

I think you would also agree that for the full-sized monopole over
perfect ground the feedpoint resistance of ~36 Ohm = radiation
resistance.

My results, all around, did not require perfection, and in fact,
nothing was resolvable through perfection if you would review that
recent post.

As an old (sorry [g]) metrologist, you're very familiar with
substitution, so let's set Rl = 0 (lossless case) and eta to 0.5 (-3
dB). Per Eq. 1, Rg = Rr.

This old metrologist found the very simple answer that eluded others
who simply took it on faith and stumbled for reason. My substitution
resolved the situation (aka the sniffer antenna which served admirably
to function as what you would appreciate as a "transfer standard").

So in our model, if I add a simulated ground resistance, Rg, that
reduces the gain by 3 dB, I have by substitution, determined the
radiation resistance.

Sure enough, if I add a 36 Ohm load at the bottom of the perfect 1/4
wave monopole, the gain drops to 2.14 dBi, and the feedpoint
resistance doubles.

I will let you try this with the other cases. I trust you will find
that the radiation resistance does decrease with shorter radiators
and/or lower loading points.

I hope I demonstrated your trust was merited.

I too I would appreciate other effort in kind to correct any
oversights I've made.

Each in our own way. Sorry to hear about your friend.

73's
Richard Clark, KB7QHC

On Sat, 6 Nov 2004 20:29:38 +0000 (UTC), "Reg Edwards"
wrote:
[snip]
|
|But by now rattle snakes must be becoming, like Bengal tigers and red
|indians, an endanged species. ;o)

Alas, no. While I have a few firearms about, my weapon of choice for
rattlesnakes is the ever popular square-nosed shovel. I have several
of these and during the snake season have one near each entrance to
the abode and one at the gate into the vegetable garden.

The score so far for 2004, Wes 2, snakes 0.

On Sat, 06 Nov 2004 18:21:52 -0600, Cecil Moore
wrote:

|Lee Hopper wrote:
|
| Cecil Moore wrote:
| I was actually one of the older California hippies
| in the 70's, full of peace and free love.
|
| I'd like to see a picture, please.
|
|A picture of the free love?

No, of your house full of cockroaches, flies, spiders.....

I don't have the time right now to comment fully, but I can make a
couple of comments now on the last part. I think I see what at least one
source of confusion might be, and hope I can clarify it a bit.

Richard Clark wrote:
. . .

Now, let us return to a point of analytical bias that lead me to
believe no apparent change in Rr was observable. In fact there was
no way to make it observable except through the artifice of my
sniffer antenna. For the model of the constant current generator, it
is a truism that gain (that is true gain for a system and not simply
antenna directivity) must increase for the same excitation.

The difference between gain relative to isotropic (which you're
unnecessarily calling "true gain") and directivity is only the
efficiency. If loss is zero, the gain and directivity are the same. If
there's 3 dB loss, for example, then the gain relative to isotropic is 3
dB less than the directivity.

I need to insert a reminder here for readers who aren't as familiar with
the terms as some of the rest of us. There isn't a single value of gain
for any antenna. First, it's nearly always different in different
directions. Second, the gain depends on the reference antenna, so you
can have just about any gain you want, just by choosing the reference.
EZNEC, NEC-2, and most professional publications use a theoretical
isotropic antenna as the reference, resulting in gain in dBi. The main
reasons for this are that it's unambiguous -- everyone agrees on what it
means -- and it makes it easy to calculate field strength from gain and
vice-versa.

Now, back to the comments. . .

It isn't true that the gain must increase as Rr increases, when the
source is a constant current. The gain relative to isotropic (reported
as dBi) is defined as the field strength from the antenna divided by the
field strength from an isotropic antenna *having the same power input*
-- converted to dB of course. As the Rr increases in your model antenna,
the power input increases if you're using a constant current source, as
you've pointed out. But the power input to the imaginary isotropic
comparison antenna increases by the same amount. The net result is no
change of gain due to the increased power input, or to the increased Rr.
What you're measuring with the "sniffer antenna" isn't the gain -- it's
the absolute field strength. To get the gain, you need to compare that
with the field strength you'd see if you applied *that same power* to an
isotropic antenna the same distance away. You should find that the power
dissipated in your sniffer antenna load is directly proportional to the
power applied to your transmit antenna. That would also be true for an
isotropic transmit antenna, so the ratio of power received from the two
antennas will stay the same as you change the transmit antenna power.

As I pointed out before, moving the load in the transmitted antenna
changes the current distribution, resulting in a very small change in
pattern shape, hence a very small change in gain. But that's the only
effect it has on gain.


After
all, we are changing the Rr either through the actuality of modified
length, or the artifice of a moving, variable load along the short
radiator. Such gain is only observable through a circuit
(broadcaster lingo for a transmit/receive pair).

In the back of my mind I was troubled about comparing situations in
dBi. Yesterday I expressed this as a possible source of confusion
for the effects sought in evidence against the obvious gain
differential. dBi is a dimensionless relation such that true gain is
washed out of the result.

No, dBi is the "true gain" expressed in dB, as explained above. It's the
field strength from the antenna compared to the field strength from an
isotropic antenna having the same input power. Simply
increasing your constant current source from 1 amp to 2 amps will
increase the signal detected by the "sniffer antenna". But I hope you
can see it's not changing the gain of the transmit antenna.

When I attempted to confirm my suspicions through field
expressions of mv/M for 1KW, I was struck that that too forced the
results to a constant power (not constant current) and thus hid the
gain demonstration in the same way. I then fell back on my practice
of employing a sniffer antenna to test reality and the data is found
above confirming the gain that would be expected. In other words,
the far field's power followed the diminution of Rr with a positive
correlation. It also followed the subsequent increase of Rr (with a
load applied to that shortened radiator) with a positive correlation.

The source of confusion or misinterpretation seems to be due to
mistaking field strength for gain. They're not the same thing. Even the
units are different -- Volts/meter or Amps/meter (or power density in
watts/square meter) for field strength, while gain and directivity are
dimensionless.

Gain would be a much less useful measure if it changed with power input.
Then, we'd have to specify the power input at which the gain is
measured. EZNEC correctly shows no gain change resulting from changing
the input power. As it is, it's easy to calculate the field strength at
any point in the far field from the gain in that direction, power input
to the antenna, and distance from it. In fact, EZNEC and NEC-2 actually
compute the fare field strength, and then derive the gain in dBi from it
by knowing the field strength from an isotropic antenna with the same
power input. Gain relative to isotropic becomes less useful in the near
field, so absolute field strengths are generally used in that region.

Roy Lewallen, W7EL

On Sun, 07 Nov 2004 00:56:00 -0800, Roy Lewallen
wrote:

The difference between gain relative to isotropic (which you're
unnecessarily calling "true gain") and directivity is only the
efficiency.

Hi Roy,

Let's call it relative gain then. The point of the matter is not in
terminology but in magnitude and correlation.

The Thread, throughout, is constituted of four principles:
Rr;
Current;
Radiator size;
Loading;

To reveal their inter-relatedness required an impartial witness of an
external load (the remote antenna which is the raison d'etre of
communication).

The gain evidenced in this remote antenna is not some arbitrary change
of terms that is alien to the craft of communication (nor even the
majority of engineering). It encompasses differences that exceed 1dB,
eclipsing that even to the point of being 7dB in the first iteration.
When in the second iteration the shortened antenna is brought to
resonance, the change still exceeds 1dB (2.9dB by my reckoning). ALL
such changes, when viewed through the veil of dBi simply reveal
miniscule changes of what you call ground reflection. As such, dBi is
a poor mechanism to reveal Rr's characteristic through structural
variations.

I won't go on with the remainder of iterations because no new
observations would be drawn. Indeed, the data supports the generality
that suits the purpose of achieving the expected results. As I
offered:

This comes as no surprise to many.

Now, the issue of Isotropism is one that is power centric, and this is
certainly the common experience of any Ham trying to load an antenna
from a real transmitter. They have a finite amount of power they wish
to maximize, and this then becomes an issue of efficiency. However,
there is NOTHING in my work that states this is a goal - or I would
have expressed that in no uncertain terms. If any seek that
divergence of issue, then my data supports it without further
qualification.

So, gain is entirely consistent within the context of the simple
agenda that was explicitly described. Gain was shown to follow
structural changes with positive correlation. Gain was shown to
follow those changes in direct proportion. Gain was shown to be
consistent with expectation. If such Gain is shown to be a wash in
efficiency at best, worst for wear, or a boon to mankind, that is
simply an issue of implementation and outside of my discussion of
examining:
Rr;
Current;
Radiator size;
Loading.

73's
Richard Clark, KB7QHC

Bart Rowlett wrote:

Hi Bart. Good post, and good to see you here again.

The electric field is vector field, characterized as having a field
strength in volts per meter dependant on spatial location, direction,
and perhaps time.

I don't understand what the term 'E-field voltage drop' could mean. Same
with 'H-field current drop'.

I think I understand what you both are saying. In the case of a
standing wave, the 'current drop' Cecil refers to (as I understand it)
is simply the current differential between two positions
Iz2 - Iz1, where I(z)=Imax(cos(wt + phi(z)), the amplitude of the
standing wave current as a function of position z. Phi being the kind
of phase which for a traveling wave varies with time at a given point,
and in this case varies with position along the standing wave. The
distinction being that Phi is not the phase of current with respect to
voltage.

The other point of disconnect between the parties hereabouts relates to
the occasional lack of distinction between the 'flow' of electrons, and
the propagational 'flow' of an EM wave.

73, Jim AC6XG

Likewise, saying that the H-field current flows and
the E-field voltage doesn't flow is nonsense.


H-field current flows?

The field H (amps per meter), is the so called magnemotive field. It
doesn't flow anymore than voltage flows through a resistor, and is
associated with the generation of magnetic flux. The magnetic flux
density, B, has the units of webers per meter squared and can be
integrated over an arbitrary surface to evaluate the total magnetic flux
passing through that surface. Magnetic flux is somewhat analogous to
current but H is not at all.

The E-field and H-field

are usually inseparable.


In the classical electromagnetic model, E & H are completely separable.
They are coupled via Faraday's law, and Maxwell's so called
displacement current. At steady state (DC) no coupling exists. When
one field quantity _varies_ in time, so will the other in accordance
with the curl equations. The coupling described by the time varying
part of the curl equations only involves the time varying components.

When determining the analysis method used to gather insight into a
physical system, one of the first considerations is to determine if the
time varying field components need to be considered, and if so, which
ones. For example, analysis of a 60 Hz power supply choke, or electric
motor, usually ignores the electric field in the air gap arising from
the time varying magnetic flux density. It's not important in the gap,
but is the driver of undesirable eddy currents in the core laminations.

bart
wb6hqk

Jim Kelley wrote:

Bart Rowlett wrote:
I don't understand what the term 'E-field voltage drop' could mean.
Same with 'H-field current drop'.

I think I understand what you both are saying. In the case of a
standing wave, the 'current drop' Cecil refers to (as I understand it)
is simply the current differential between two positions
Iz2 - Iz1, where I(z)=Imax(cos(wt + phi(z)), the amplitude of the
standing wave current as a function of position z.

Here's more what I had in mind. In a source/transmission line/
load configuration, where the loss in the transmission line is 3dB,
the load voltage and load current decrease by the same percentage.
Saying that the voltage wave dropped but the current wave didn't
drop seems a little strange to me. Also, saying the current wave
flowed but the voltage wave didn't, seems a little strange.

The signal attenuated by the transmission line has the identical
equations for voltage and current except for the 'Z0' constant. Does
that Z0 term have the power to cause the current wave to flow and
the voltage wave not to flow? Does the current wave leave the
voltage wave behind in the transmission line dust? Since RF waves
always move at the speed of light, exactly where does the voltage
wave reside when it is not moving at the speed of light and how does
it magically arrive at the load at the same time as the current wave
if it doesn't flow at the speed of light along with the current wave?
(For the humor impaired, this is pure unadulterated humor.)

Doesn't "drop" and "decrease" mean the same thing? Webster's says
they are synonyms. How can a voltage wave drop in magnitude but a
current wave cannot drop in magnitude even if it is defined as
having a constant relationship (Z0) to the voltage wave?

Doesn't "flow" and "travel" mean the same thing? How does the
voltage traveling wave get to the load without flowing? Seems if
the voltage traveling wave didn't flow along with the current
traveling wave, it would never get to the load. But, they tell me
that logic doesn't matter anymore and quantum physics rules. There's
no such thing as reflected energy anymore and only a mush of energy
ever exists. Never mind the ghosting on your TV. That is all in your
mind. Oh yeah, ghosting TV's never reach steady-state. Never mind that
radar couldn't work without reflected energy. Oh yeah, radar never
achieves steady-state. Now I understand completely!

In the classical electromagnetic model, E & H are completely
separable.

I got to wondering exactly how Bart goes about separating the E-
field from H-field in the light from the Sun before it gets to
Earth. :-) But I'm only a lowly grasshopper, trying to grok the
deep thoughts of the gurus. (As always, in good humor)
--
73, Cecil, W5DXP