Yuri`s point is proved. Look at Fig 6. The picture is worth a thousand
words.

Best regards, Richard Harrison, KB5WZI



Yes, but then on page 16-7 Fig 10 they show that current across the coil is
constant, which situation I analyze in my article at www.K3BU.us as an error
being perpetuated since 1955 by Belrose.

W8JI used this picture to "see, it is constant" :-)

I wonder if 20th edition has the same stuff. I haven't got new book yet.

Yuri

Yuri, K3BU wrote:
"W8JI used this picture (Fig 10) to "see, it is constant".

But that was only by specification. It`s the same as saying, "Let`s say
the line is lossless".

The text reads:
"The loading coil acts as the lumped constant that it is, and
disregarding losses and coil radiation, maintains the same current flow
throughout."

This says that in the impossible case of zero radiation and zero loss,
the coil current is the same at both ends of the coil. This is close
enough for a coil at 50 Hz, but unlikely at 5 MHz.

A real loading coil such as a bug catcher, has a real length. The
combination of incident and reflected waves at each point along the
length of the antenna produces a different voltage, just as seen in a
transmission line. This effect prevails in an antenna, too.

Just as on a transmission line, the voltage variation represents an
impedance variation. Impedance is high at the open-circuit end of the
antenna , and it it is low 90-degrees back from that open circuit. Since
some length is filled with the coil, there is a difference in volts at
the ends of the coil due to the standing wave on the antenna.

The feed paths to the coil are unbalanced as shown in Fig 6. That is not
shown in Fig 10 which is meant to show the difference in antenna current
above and below the coil, not what happens in the coil itself. The
authors specify an idealized coil which has the same current in and out.
This is only a declaration, not a real world situation.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
This says that in the impossible case of zero radiation and zero loss,
the coil current is the same at both ends of the coil.

This would be true for traveling-wave antennas. But in a standing-wave
antenna, the net current is the sum of the forward current and the
reflected current. Even if the coil had zero radiation and zero loss,
a real-world coil would have a delay through the coil. That delay
changes the relative phase between the forward and reflected currents
making the net current different at each end of the coil even for a
coil with zero radiation and zero loss. The forward currents would be
equal into and out of the coil. The reflected currents would be equal
into and out of the coil. But their phasor sum would differ due to
phasing.

Assume the forward current and reflected current are in phase at zero
degrees at the feedpoint. The net current is simply the algebraic sum of
those two values. But 45 degrees out from the feedpoint, the forward
current is at 45 degrees and less than at the feedpoint. The reflected
current is at -45 degrees and greater than at the feedpoint and the
sum of the two currents is the sum of two phasor currents 90 degrees
apart. At 90 degrees, at the end of the antenna, the forward current
and reflected current are equal and phasor sum to zero.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Richard Harrison wrote:
Yuri, K3BU wrote:
"W8JI used this picture (Fig 10) to "see, it is constant".

But that was only by specification. It`s the same as saying, "Let`s say
the line is lossless".

I looked at the ARRL Antenna Book CD and it contains the same
stuff. It also says: "This product is licensed under the terms
of the License Agreement contained in the LICENSE.TXT file on
the disk. Read it carefully before using the CD." :-)
--
73, Cecil, W5DXP

Read it carefully before using the CD." :-)

I didn't use CD, just book 19th Ed.

BUmmer

Cecil, W5DXP wrote:
"I looked at the ARRL Antenna Cook CD and it contains the same stuff."

Declaring a coil to have zero size and loss does not make it so.

Loss resistance alone does not delay anything. It kills electricity by
converting it to heat instantly. It takes no prisoners. It has no
electrical storage.

Pure inductance delays current by exactly 90-degrees behind the applied
a-c voltage. Resistance adds vectorially with inductive reactance to
produce an impedance on some angle with the resistance between 0 and
90-degrees, depending upon the magnitudes of resistance and reactance.

So, in any coil the current is delayed. Coax with a coiled center
conductor is manufactured as delay line and is specified in microhenries
per foot.

Coils are made of conductors which suffer skin effect resistance. None
escape loss, despite declarations. None occupy zero space.

Assuming perfection is valuable for analysis, but should not be used as
proof of performance.

Best regards, Richard Harrison, KB5WZI