Phase Shift through a 75m Texas Bugcatcher Coil
 

On Fri, 11 May 2007 20:09:35 GMT, Cecil Moore
wrote:

I have been telling Roy for years that
his and w8ji's standing-wave current measurements were bogus
so he cannot possibly plead ignorance. Now EZNEC agrees with
me. Poetic justice?

Only if a whore could rhyme.

Phase Shift through a 75m Texas Bugcatcher Coil
 

On May 11, 7:44 am, John Smith I wrote:
wrote:
do you now how to explain this so normal people can understand?

If traveling waves are used to measure phase shift though the coil in
question reliable data is obtained on phase shift.

If standing waves are used, the data is flawed.

Well, you asked for simple now, didn't you?

Regards,
JS

no i didn'tt ask for simple. i asked for an explanation that could be
understood. So far i don't see any comparisons of what makes 'bad'
data bad, only reasons. everuyone has reasons. reliable? flawed?
is this like ~2db? how flawed is ~?

Phase Shift through a 75m Texas Bugcatcher Coil
 

facts don't make very good explanations.

On May 11, 7:50 am, John Smith I wrote:
wrote:
do you now how to explain this so normal people can understand?

One more simple "fact."

Standing waves are really not "standing." They are "moving in place."
(well, oscillating, actually)

silly-grin
JS

Phase Shift through a 75m Texas Bugcatcher Coil
 

Phase Shift through a 75m Texas Bugcatcher Coil
 

On Fri, 11 May 2007 19:56:27 -0700, John Smith I
wrote:

wrote:
facts don't make very good explanations.

I found Cecils' .ez files (the excel sheets require the microsoft
product which some may not have access to) were an excellent
"explanation" of what he proposes.

Talk about the gulf between perception and reality.

73's
Richard Clark, KB7QHC

Phase Shift through a 75m Texas Bugcatcher Coil
 

Herbert wrote:
"Do you know how to explain this so normal people can understand?"

I `m not a Guru, but I`ll try.

First, there was adispute about delay in an antenna loading coil. That
provoked attempts to measure the delay. Then the argument turned to the
measurement methods.

The antenna signal travels from the transmitter through the coil and
through the stinger until it reaches the tip where it is forced to
reverse course by the open circuit. All the signal which has not been
radiated or lost in waste enroute starts its journey back toward the
transmitter. This reflected energy from the antenna tip is of no help in
determining delay through the loading coil but the ripples it makes,
when it adds and subtracts from the waveform of the forward energy,
makes measurements difficult. Frequently a directional coupler is used
to measure the energy moving in one direction, while ignoring the energy
moving in the opposite direction, to get a meaningful measurement. Cecil
proposed a resistor matching the impedance at the tip of the antenna to
avoid a reflection. This also eliminates the troublesome ambiguity.

Testing is convincing, perhaps, but not really necessary as the delay
through a coil has been understood and quantified at least since Ampere
who died in 1836.

The ARRL Handbook, mine is from 1976, explains inductance on page 25:
"Since the induced emf opposes the emf of the source, it tends to
prevent the current from rising rapidly when the circuit is closed."

Delay is a well known function of inductors. In early times they were
often called "retard coils".

Best regards, Richard Harrison, KB5WZI

Phase Shift through a 75m Texas Bugcatcher Coil
 

John Smith I wrote:
Makes you wonder if they bother to download the free
trial version of EZNEC and bother to look ...

The bugcatcher coil in coil505.EZ has 234 segments.
The free demo version of EZNEC is limited to 20
segments. Thus, something like a 2-4 turn helix
is all the free demo version will support.
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Richard Harrison wrote:
Cecil
proposed a resistor matching the impedance at the tip of the antenna to
avoid a reflection. This also eliminates the troublesome ambiguity.

Actually a little more elementary than that. Take a base-loaded
75m mobile antenna and remove the stinger, leaving only the
coil. Install a resistor to ground from the top of the coil and
adjust the resistor value equal to the characteristic impedance
of the coil. This is the point where the feedpoint impedance
at the base of the coil is equal to the value of the resistor
in ohms. This is, of course, assuming the coil is less than
1/4WL long which it is for a typical mobile installation.
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

What Happens if the Bug Catcher actually catches a Bug. How does that
change things ?? :-)
"Cecil Moore" wrote in message
t...
Richard Harrison wrote:
Cecil
proposed a resistor matching the impedance at the tip of the antenna to
avoid a reflection. This also eliminates the troublesome ambiguity.

Actually a little more elementary than that. Take a base-loaded
75m mobile antenna and remove the stinger, leaving only the
coil. Install a resistor to ground from the top of the coil and
adjust the resistor value equal to the characteristic impedance
of the coil. This is the point where the feedpoint impedance
at the base of the coil is equal to the value of the resistor
in ohms. This is, of course, assuming the coil is less than
1/4WL long which it is for a typical mobile installation.
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

"Richard Harrison" wrote in message
...
The antenna signal travels from the transmitter through the coil and
through the stinger until it reaches the tip where it is forced to
reverse course by the open circuit. All the signal which has not been
radiated or lost in waste enroute starts its journey back toward the
transmitter. This reflected energy from the antenna tip is of no help in
determining delay through the loading coil but the ripples it makes,
when it adds and subtracts from the waveform of the forward energy,
makes measurements difficult. .....

Best regards, Richard Harrison, KB5WZI


Which brings me back to my question: How important is the Q and low
resistance of the coil and stinger? The subtracted waveform (current) seems
to show slight increase at the base of coil, which we are trying to
achieve - prolonging the high current portion along the radiator system.

If we had traveling wave situation along the radiator - almost uniform
distribution (need resistive loading at the tip, just like in Cecil's coil
example or Rhombic/Beverage antennas) - how would that affect overall
efficiency?

When Barry, W9UCW did his experiments and measurements, he was surprised
that quality of the loading coil made hardly any difference. Like good
Bugcatcher coil vs. bad Hustler type resonator.

Do we have the case where some power is being lost for the benefit of
stretching the high current portion along the radiator and making up for
losses?
Normally we always try to minimize the resistive or other loses, but seems
that something "fishy" might be going on, or is it insignificant form
practical purposes, but I still believe that when involving more loaded
elements in an array, things add up and become worthy of considering.
(We are talking about quarter wave vertical resonant radiator not the
Goosian soup :-)

73 Yuri, K3BU.us