Miller effect - was: What is the antenna current path or route
 

Dear Group:

A hot button has been pushed. The Miller effect (not to be overly
confused with the Miller theorem) stems from an exhaustive analysis of the
amplification vs. frequency of very low mu triode amplifiers (the tubes
available at the time). The work was published just after WW-1! It was
noted that the effect on frequency response of the capacitance between grid
and plate was magnified by the amplification of the stage. Miller's paper
showed that the effect of the aforementioned capacitance could be
approximated by a capacitor in series with a resistance with the combination
placed in shunt with the grid-cathode. Several conditions need to be true
that were overlooked by later commentators!

Many years latter, Miller's work became corrupted into Miller's theorem
that erroneously contended that the effect of the feedback capacitor was the
same as a gain dependent capacitor in shunt with the input and output of the
amplifier. Various "proofs" have been published that "prove" Miller's
theorem. They remind one of HS proofs involving dividing by zero.

It is true that the frequency effect of capacitance between input and
output (note, those are nouns) of an amplifier is detrimentally increased as
the gain of the amplifier increases. [as gain goes up - the upper
half-power frequency goes down] [note the notion of approximately constant
gain-bandwidth product for well behaved amplifiers]
However, the simple modeling indicated by "Miller's theorem" only
occasionally estimates the relationship between feedback capacitance and
upper half-power frequency. Fortunately, the allege convenience of using
Miller's theorem in the slide rule days has now gone away. Today, one may
use PSpice (or the like) and receive close estimates of the expected
performance of an amplifier.

It is difficult for me to see gain at the end of an antenna's wire. The
apparent capacitance that exists at the end of an antenna's wire simply
exists and is not magnified by anything.

Lecture mode off. 73, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:

"Richard Harrison" wrote in message
...

snip
Energy from the magnetic field is converted to energy in the electric
field for an instant (Cecil`s famous conservation of energy). This
produces an insreased voltage at the open circuit end. This incresed
voltage has more capacitive effect, akin to the "Miller effect" caused
by the higher signal voltage on the plate of an amplifier vacuum tube
than on its grid.

snip


Best regards, Richard Harrison, KB5WZI

Miller effect - was: What is the antenna current path or route
 

Mac, N8TT wrote:
"It is difficult for me to see gain at the end of sn antenna wire."

Miller effect works in a triode tube by placing a larger signal voltage
on the plate than on its grid. This increases the difference in number
of electrons between grid and plate.

The charge of a capacitor is the difference in number of electrons on
the two plates.

At the open circuit end of a 1/4-wave antenna, the incident and
reflected voltages are in-phase and equal in magnitude, thus doubling
voltage at the antenna tip. This increased voltage doubles the charge at
that point over that produced by the incident voltage alone as Q=CE.

Mac is right. There is no mu factor in an antenna tip but there is a
voltage and charge gain.

Best regards, Richard Harrison, KB5WZI

Miller effect - was: What is the antenna current path or route
 

On 20 Oct, 07:50, (Richard Harrison) wrote:
Mac, N8TT wrote:

"It is difficult for me to see gain at the end of sn antenna wire."

Miller effect works in a triode tube by placing a larger signal voltage
on the plate than on its grid. This increases the difference in number
of electrons between grid and plate.

The charge of a capacitor is the difference in number of electrons on
the two plates.


But a capacitor doesnot radiate.....the hole is getting deeper !



At the open circuit end of a 1/4-wave antenna, the incident and
reflected voltages are in-phase and equal in magnitude, thus doubling
voltage at the antenna tip. This increased voltage doubles the charge at
that point over that produced by the incident voltage alone as Q=CE.

Mac is right. There is no mu factor in an antenna tip but there is a
voltage and charge gain.

Best regards, Richard Harrison, KB5WZI

Miller effect - was: What is the antenna current path or route
 

Art wrote:
"But a capacitor does not radiate....."

Depends entirely on the size and configuration.
Please see pages 83 through 93 of "Transmission Lines, Antennas, and
Wave Guides" by R.W.P King, Mimno, and Wing.

Best regards, Richard Harrison, KB5WZI

Miller effect - was: What is the antenna current path or route
 

Richard Harrison wrote:
Art wrote:
"But a capacitor does not radiate....."

Depends entirely on the size and configuration.

Yep, one of the the reasons for SMD caps is that
the leads on conventional caps radiate at UHF+
frequencies.
--
73, Cecil http://www.w5dxp.com

Miller effect - was: What is the antenna current path or route
 

"art" wrote in message
ps.com...
On 20 Oct, 07:50, (Richard Harrison) wrote:
Mac, N8TT wrote:

"It is difficult for me to see gain at the end of sn antenna wire."

Miller effect works in a triode tube by placing a larger signal voltage
on the plate than on its grid. This increases the difference in number
of electrons between grid and plate.

The charge of a capacitor is the difference in number of electrons on
the two plates.


But a capacitor doesnot radiate.....the hole is getting deeper !

don't tell the designers of those funny little cross field antennas that!
their whole theory depends on capacitors creating a ratiating electric field
which then combines with their separately created magnetic field to create
an em wave.

Miller effect - was: What is the antenna current path or route
 

On 20 Oct, 13:00, (Richard Harrison) wrote:
Art wrote:

"But a capacitor does not radiate....."

Depends entirely on the size and configuration.
Please see pages 83 through 93 of "Transmission Lines, Antennas, and
Wave Guides" by R.W.P King, Mimno, and Wing.

Best regards, Richard Harrison, KB5WZI

Is this going to be the same garbage that you troted out from
Terman? You still haven't explained why you accepted that there
was high impedance at the top preventing current flow.
The impedance down the center is very low, just the
resistance of the copper or aluminium. When will you be ready to
give the correct interpretation using this new capacitance aproach?
Have we dismissed Miller. Most will agree with the side note you added
regarding what the charge of a capacitor is to which I will
add that there are more Irishmen in London than in Dublin.
Also Scotland has the highest red heds per capitor than anywhere
in the rest of the world but none of these facts have nothing to do
with respect to your wrong readings of Terman. Now you are bringing
forward a new book to take the place of Terman to prove something
that is not relavent to the fact why you posted erronius info.

Miller effect - was: What is the antenna current path or route
 

On 20 Oct, 13:29, Cecil Moore wrote:
Richard Harrison wrote:
Art wrote:
"But a capacitor does not radiate....."

Depends entirely on the size and configuration.

Yep, one of the the reasons for SMD caps is that
the leads on conventional caps radiate at UHF+
frequencies.
--
73, Cecil http://www.w5dxp.com

The capacitor itself does not radiate ie what is
between the two plates but the size of a capacitor does matter when
releasing its charge that creates radiation. Since the time variance
of the charge release is what creats radiation it follows that the
size
of and the constrictions provided make a huge difference. (Read up on
Bernollis
and his work on fluids)
You can have a very small inductance with a very large capacitance
as the L.C. ratio stays intact but the time variance of energy
release
will certainly different in that moment of time when the radiation
pulse occurs
As with standard practices I am not taking into account the
inductance
of the capacitor plates themselves since it just provides an outlet
for posters to avoid repeat of past errors by changing the subject
Best regards
Art

Miller effect - was: What is the antenna current path or route
 

Art Wrote:
"You still haven`t explained why you accepted that there was high
impedance at the top preventing current flow."

Readers of this thread already know that there is a class of materials
known as insulators and that free-space and the earth`s atmosphere
belong to that class even though they are mostly immaterial.

If you would read the pages I suggested from R.W.P. King`s writing in
his section on Antennas in "Transmission Lines, Antennas, and Wave
Guides, you will find: 1. Electric Charges and Currents and the
Electromagnetic Field, 2. The General Law of Electromagnetic Action, 3.
Special Case of the Near Zone, 4. Special Case of the Far Zone, 5. Far
Zone, 6. Closed and Open Circuits, 7. Properties of an a
Antenna, 8. Leading Term in the Distribution of Current and Charge along
a Center-driven Highly Conducting Antenna of Extremely Small Radius, 9.
Distribution of Current along a Symmetrical Antenna of Small Radius, 10.
Input Self-Impedance of Symmetrical Center-drive. Antenna of Small
Radius.

Those numbered items are just the titles of the sections which are
filled with text and illistrations which clarify the issues discussed in
this thread. I`ll leave it to the reader to search out the wealth of
information contained therein.

Best regards, Richard Harrison, KB5WZI

What is the antenna current path or route
 

Art wrote:
"Still you can`t blame them if all they know comes from the ARRL books.
After all it is a hobby and in the early days many did not have an
opportunity for a college education."

Despite Art`s disdain for amateurs, I`ve found solid information in the
"ARRL Antenna Book". Mine contains Characteristics of a lambda/4
monopole which includes: "The current in a lambda/4 monopole varies
practically sinusoidally (as is the case with a lambda/2 wire), and is
highest at the ground-plane connection. The RF voltage, however is
highest at the open (top) end and minimum at the ground-plane
connection." The reason for this is already given in this thread.

Best regards, Richard Harrison, KB5WZI