(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?
===============================

(Rhetorical Answer)
It can't. Are you trying to insinuate I've ever said that it could?

But I'm pleased to see you are getting nearer to understanding how to model
a loading coil in an antenna wire. After all, the concept is simplicitly
itself to any electrical engineer worth his salt. And it's intuitively
obvious it's the only way of going about the job. Your 'cosine formula'
automatically comes out in the wash. As Holmes said to Watson. ;o)

Incidentally, from memory, in the 1950's, in the IEEE "Reference Data for
Radio Engineers" there was an article on short helically-wound antennas,
giving number of turns for a given height of 1/4-wave resonance. The author
was on the right track. But there were errors in the formulae which had not
been arrived at by analytical means.
----
Reg, G4FGQ

Reg Edwards wrote:
(Rhetorical Question)

Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?

(Rhetorical Answer)
It can't. Are you trying to insinuate I've ever said that it could?

Nope, but others have asserted such. What would be a ballpark figure
for the Z0 of a bugcatcher loading coil?

Incidentally, from memory, in the 1950's, in the IEEE "Reference Data for
Radio Engineers" there was an article on short helically-wound antennas,
giving number of turns for a given height of 1/4-wave resonance. The author
was on the right track. But there were errors in the formulae which had not
been arrived at by analytical means.

I just happen to have a 1957 copy from college days. Interestingly, it has
a velocity of propagation formula for the helix that includes axial velocity.
Didn't someone say axial velocity doesn't control the speed of propagation
for a loading coil?
--
73, Cecil http://www.qsl.net/w5dxp



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Reg wrote,

The ONLY way of modelling the effect of a loading coil in an antenna wire is
to consider it to be a section of a continuous-inductance-loaded
transmission line which also has a radiation resistance.


Another absolutist, fairly assinine statement from across the pond. How do
you know it's the ONLY way, Reg, have you tried any others?

Tom Donaly, KA6RUH

"Tdonaly"
Reg wrote,

The ONLY way of modelling the effect of a loading coil in an antenna wire
is
to consider it to be a section of a continuous-inductance-loaded
transmission line which also has a radiation resistance.


Another absolutist, fairly assinine statement from across the pond. How do
you know it's the ONLY way, Reg, have you tried any others?

Tom Donaly, KA6RUH

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

Tom, beware the Green-eyed Technology Goddess.

WE have modelling programs which actually WORK.

And FREE to US citizens.

Is this 'dumping' of shoddy goods?

After gigabytes upon gigabytes of civil war amongst yourselves - YOU
havn't!
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg Edwards, G4FGQ wrote:
"It has a uniformly distributed radiation resistance according to the
length of the coil form."

That may be the case of "treating" radiation resistance as if uniformly
distributed. Radiation resistance may be defined as the resistance which
would take the same power as that radiated when placed at the
high-current point of the antenna.

While a transmission line of uniform cross section may have uniform
inductance and capacitance per unit length, it is unlikely that an
antenna has uniform capacitance per unit length. Electric field lines of
force have a varying concentration along equal small segments of wire
length. It`s usually a function of distance between wires and this
varies in an antenna because the antenna is meant to radiate.

Variation of capacitance along an antenna causes a variation in surge
impedance along the antenna, but a useful average can be used for
calculations. Straight wire or coiled as in a rubber ducky, an antenna
is subject to this variation in capacitance and surge impedance.

Best regards, Richard Harrison, KB5WZI

Richard, it's only a model - and it WORKS very well.

"If you know of a better hole then go to it." - Bruce Bainsfather,
newspaper cartoonist, caption of a cartoon in the trenches, mud and
shrapnel, Belgium, WW1. ;o)
----
Yours, Reg.
=============================


"Richard Harrison" wrote in message
...
Reg Edwards, G4FGQ wrote:
"It has a uniformly distributed radiation resistance according to the
length of the coil form."

That may be the case of "treating" radiation resistance as if uniformly
distributed. Radiation resistance may be defined as the resistance which
would take the same power as that radiated when placed at the
high-current point of the antenna.

While a transmission line of uniform cross section may have uniform
inductance and capacitance per unit length, it is unlikely that an
antenna has uniform capacitance per unit length. Electric field lines of
force have a varying concentration along equal small segments of wire
length. It`s usually a function of distance between wires and this
varies in an antenna because the antenna is meant to radiate.

Variation of capacitance along an antenna causes a variation in surge
impedance along the antenna, but a useful average can be used for
calculations. Straight wire or coiled as in a rubber ducky, an antenna
is subject to this variation in capacitance and surge impedance.

Best regards, Richard Harrison, KB5WZI