Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old November 29th 07, 05:42 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 274
Default Loading Coils; was : Vincent antenna

Gene Fuller wrote:
Cecil Moore wrote:
Tom Donaly wrote:
What is the characteristic impedance of Tom's coil?


A few thousand ohms. Use equation 50 at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

What's your formula for the velocity factor of Tom's coil? Is it from
the same Tesla coil crackpot you quoted in previous posts?


Do you reject all IEEE white papers? The formula
is equation 32.


Cecil,

Have you actually read and understood that article? Corum mentions
several times that everything he reduces to the simple formulas applies
only to quarter-wave resonance conditions.

Look at the author's highlight between equations 31 and 32. Look at the
discussion near equation 47. Look at the discussion following equation
60. Read the entire discussion in section 5.

Note that he does not say the characteristic impedance is a constant
that can be deduced from resonance conditions and then applied to
operating conditions. In fact, he says exactly the opposite.

"It is worth noting that, for a helical anisotropic wave guide, the
effective characteristic impedance is not merely a function of the
geometrical configuration of the conductors (as it would be for lossless
TEM coaxial cables and twin-lead transmission lines), but it is also a
function of the excitation frequency."

I have no comment on the validity of the Corum analysis. He makes a lot
of approximations and simplifications which may or may not be completely
correct. However, it is clear that you are mis-quoting him.


73,
Gene
W4SZ


The Corum duo model their Tesla coil as "an isotropically conducting
cylindrical boundary." Later, they call it a "helically disposed surface
waveguide." Later, they write, "Further, the Tesla coil passes to a
conventional lumped element inductor as the helix is electrically
shortened." Do the first two quotes resemble a description of a
typical ham antenna loading coil? Has anybody here used a Tesla coil
to load an antenna? The Corums also state in one part of their paper
that their method of analysis is "fraught with danger." Indeed.
Cecil's misuse of the formulas certainly proves that.
Many people over the years have done just fine loading their antennas
with lumped inductors. There's no need to put a "helically disposed
surface waveguide" on a mobile antenna, and if someone thinks that
modeling a coil as "an isotropically conducting cylindrical boundary"
actually turns that coil into an isotropically conducting cylindrical
boundary, that someone should seek help.
73,
Tom Donaly, KA6RUH
  #2   Report Post  
Old November 29th 07, 06:25 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Loading Coils; was : Vincent antenna

Tom Donaly wrote:
Many people over the years have done just fine loading their antennas
with lumped inductors.


That's not the point of this discussion, Tom. The
only question that needs to be answered here is:
Can a 2" dia, 100 T, 10" long loading coil have
a delay of 3 nS through it at 4 MHz? Do you support
such a technical absurdity? The Corum IEEE white
paper suggests that delay is in error by a magnitude.

All of the boundary test conditions given in Corum's
IEEE white paper are satisfied by a 75m bugcatcher
loading coil. There is no reason to believe that
the underlying principles of physics do not apply.
In fact, the diagram of the 1/4WL resonant system
looks exactly like a base loading coil, stinger,
and top hat as is used for 75m mobile operation.
--
73, Cecil http://www.w5dxp.com
  #3   Report Post  
Old November 29th 07, 07:51 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 274
Default Loading Coils; was : Vincent antenna

Cecil Moore wrote:
Tom Donaly wrote:
Many people over the years have done just fine loading their antennas
with lumped inductors.


That's not the point of this discussion, Tom. The
only question that needs to be answered here is:
Can a 2" dia, 100 T, 10" long loading coil have
a delay of 3 nS through it at 4 MHz? Do you support
such a technical absurdity? The Corum IEEE white
paper suggests that delay is in error by a magnitude.

All of the boundary test conditions given in Corum's
IEEE white paper are satisfied by a 75m bugcatcher
loading coil. There is no reason to believe that
the underlying principles of physics do not apply.
In fact, the diagram of the 1/4WL resonant system
looks exactly like a base loading coil, stinger,
and top hat as is used for 75m mobile operation.


Do you really believe that an antenna + loading coil has
to be a quarter wave long to resonate?
73,
Tom Donaly, KA6RUH
  #4   Report Post  
Old November 29th 07, 08:32 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Loading Coils; was : Vincent antenna

Tom Donaly wrote:
Do you really believe that an antenna + loading coil has
to be a quarter wave long to resonate?


Note: I am NOT talking about *physical* lengths.
The phase shift from feedpoint to tip has to be
*electrically 90 degrees* so the answer is yes.
For a base-loaded mobile antenna, the sum of the
phase shifts a

PS1. The phase shift through the loading coil.
PS2. The phase shift at the coil to stinger junction.
PS3. The phase shift in the stinger.

PS1 + PS2 + PS3 = 90 degrees.

In a typical 75m base-loaded mobile antenna, PS1
may be about 40 degrees, PS2 about 40 degrees, and
PS3 about 10 degrees.

PS2 is a freebie lossless phase shift compliments of
Mother Nature caused by the impedance discontinuity
between the coil and the stinger. If that phase shift
can be maximized, it should add to antenna efficiency.
--
73, Cecil http://www.w5dxp.com
  #5   Report Post  
Old November 29th 07, 10:45 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 274
Default Loading Coils; was : Vincent antenna

Cecil Moore wrote:
Tom Donaly wrote:
Do you really believe that an antenna + loading coil has
to be a quarter wave long to resonate?


Note: I am NOT talking about *physical* lengths.
The phase shift from feedpoint to tip has to be
*electrically 90 degrees* so the answer is yes.
For a base-loaded mobile antenna, the sum of the
phase shifts a

PS1. The phase shift through the loading coil.
PS2. The phase shift at the coil to stinger junction.
PS3. The phase shift in the stinger.

PS1 + PS2 + PS3 = 90 degrees.

In a typical 75m base-loaded mobile antenna, PS1
may be about 40 degrees, PS2 about 40 degrees, and
PS3 about 10 degrees.

PS2 is a freebie lossless phase shift compliments of
Mother Nature caused by the impedance discontinuity
between the coil and the stinger. If that phase shift
can be maximized, it should add to antenna efficiency.


So, since the phase shift has to be 90 degrees, the antenna
should always resonate at the same frequencies a quarter wave
stub of the same electrical length would resonate at, right?
73,
Tom Donaly, KA6RUH


  #6   Report Post  
Old November 30th 07, 12:34 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Loading Coils; was : Vincent antenna

Tom Donaly wrote:
So, since the phase shift has to be 90 degrees, the antenna
should always resonate at the same frequencies a quarter wave
stub of the same electrical length would resonate at, right?


Not sure what you mean by this statement. 90 degrees
is 90 degrees. A mobile antenna physically shorter
than 1/4WL is still close to 90 degrees long at
resonance. (It is not exactly 90 degrees because of
the well-known end effects.)

In order for the reflected wave to be in phase with
the forward wave at the feedpoint (purely resistive
feedpoint impedance), the reflected wave must traverse
180 *electrical degrees* during its round trip. That
fact inticates that the antenna is electrically 90
degrees long.
--
73, Cecil http://www.w5dxp.com
  #7   Report Post  
Old November 29th 07, 11:46 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 440
Default Loading Coils; was : Vincent antenna

"Cecil Moore" wrote
All of the boundary test conditions given in Corum's
IEEE white paper are satisfied by a 75m bugcatcher
loading coil. There is no reason to believe that
the underlying principles of physics do not apply.
In fact, the diagram of the 1/4WL resonant system
looks exactly like a base loading coil, stinger,
and top hat as is used for 75m mobile operation.

_____________

Cecil,

Do you believe that a 75m mobile antenna system using an artificially
resonant (as in bugcatcher-loaded), electrically short whip produces the
same elevation pattern and groundwave field strength at 1 km as an unloaded
1/4-wave vertical monopole for 75m with the same applied power using a good,
buried radial r-f ground (say, 2 ohms or less)?

RF


  #8   Report Post  
Old November 30th 07, 12:48 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Loading Coils; was : Vincent antenna

Richard Fry wrote:
Do you believe that a 75m mobile antenna system using an artificially
resonant (as in bugcatcher-loaded), electrically short whip produces the
same elevation pattern and groundwave field strength at 1 km as an unloaded
1/4-wave vertical monopole for 75m with the same applied power using a good,
buried radial r-f ground (say, 2 ohms or less)?


No, the radiation pattern depends upon the *physical*
length. The feedpoint impedance depends upon the
*electrical* length. (I haven't said anything about
the radiation pattern in my postings.) Unless the
antenna is "full-sized", the physical length and
electrical length are different.

There is a free lossless phase shift between the top
of a loading coil and the stinger. There's obviously
zero radiation from that dimensionless point. That 40
electrical degrees of antenna is not physically there
so it cannot radiate.
--
73, Cecil http://www.w5dxp.com
  #9   Report Post  
Old November 29th 07, 08:42 PM posted to rec.radio.amateur.antenna
art art is offline
external usenet poster
 
First recorded activity by RadioBanter: Sep 2006
Posts: 1,188
Default Loading Coils; was : Vincent antenna

On 29 Nov, 09:42, "Tom Donaly" wrote:
Gene Fuller wrote:
Cecil Moore wrote:
Tom Donaly wrote:
What is the characteristic impedance of Tom's coil?


A few thousand ohms. Use equation 50 at:


http://www.ttr.com/TELSIKS2001-MASTER-1.pdf


What's your formula for the velocity factor of Tom's coil? Is it from
the same Tesla coil crackpot you quoted in previous posts?


Do you reject all IEEE white papers? The formula
is equation 32.


Cecil,


Have you actually read and understood that article? Corum mentions
several times that everything he reduces to the simple formulas applies
only to quarter-wave resonance conditions.


Look at the author's highlight between equations 31 and 32. Look at the
discussion near equation 47. Look at the discussion following equation
60. Read the entire discussion in section 5.


Note that he does not say the characteristic impedance is a constant
that can be deduced from resonance conditions and then applied to
operating conditions. In fact, he says exactly the opposite.


"It is worth noting that, for a helical anisotropic wave guide, the
effective characteristic impedance is not merely a function of the
geometrical configuration of the conductors (as it would be for lossless
TEM coaxial cables and twin-lead transmission lines), but it is also a
function of the excitation frequency."


I have no comment on the validity of the Corum analysis. He makes a lot
of approximations and simplifications which may or may not be completely
correct. However, it is clear that you are mis-quoting him.


73,
Gene
W4SZ


The Corum duo model their Tesla coil as "an isotropically conducting
cylindrical boundary." Later, they call it a "helically disposed surface
waveguide." Later, they write, "Further, the Tesla coil passes to a
conventional lumped element inductor as the helix is electrically
shortened." Do the first two quotes resemble a description of a
typical ham antenna loading coil? Has anybody here used a Tesla coil
to load an antenna? The Corums also state in one part of their paper
that their method of analysis is "fraught with danger." Indeed.
Cecil's misuse of the formulas certainly proves that.
Many people over the years have done just fine loading their antennas
with lumped inductors. There's no need to put a "helically disposed
surface waveguide" on a mobile antenna, and if someone thinks that
modeling a coil as "an isotropically conducting cylindrical boundary"
actually turns that coil into an isotropically conducting cylindrical
boundary, that someone should seek help.
73,
Tom Donaly, KA6RUH- Hide quoted text -

- Show quoted text -


Tom,
May I point out that a Tesla coil is an "antenna" that does not
conform
to Maxwells laws with respect to the adherance to the LC ratio.
The LC ratio is out of balance such that the capacitor is not
of the correct size to store and then return the imposed energy from
the inductive heavy coil which is visually seen as resulting in a
spark.
Regards
Art
  #10   Report Post  
Old November 30th 07, 07:01 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 801
Default tesla coils antennas maxwell Loading Coils; was : Vincent antenna


Tom,
May I point out that a Tesla coil is an "antenna" that does not
conform
to Maxwells laws with respect to the adherance to the LC ratio.
The LC ratio is out of balance such that the capacitor is not
of the correct size to store and then return the imposed energy from
the inductive heavy coil which is visually seen as resulting in a
spark.
Regards
Art


Huh...

tesla coils follow all of Maxwells equations quite nicely. Paul
Nicholson did some very nice analysis on this a few years back,
published at a link previously posted.

They're two coupled LC resonant circuits, with the coupling adjusted to
around k=0.2. There are higher order systems with 3 or more resonators,
as well (called Magnifiers in the TC world)

The challenge in spark making is choosing appropriate operating
parameters (coupling, radius of curvature, topload capacitance, etc.) to
optimally promote spark growth.


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Single Wire Antenna {Longwire / Random Wire Antenna} - What To Use : Antenna Tuner? and/or Pre-Selector? RHF Shortwave 20 December 31st 05 09:41 PM
Single Wire Antenna {Longwire / Random Wire Antenna} - What To Use : Antenna Tuner? and/or Pre-Selector? David Shortwave 0 December 28th 05 05:24 AM
Single Wire Antenna {Longwire / Random Wire Antenna} - What To Use : Antenna Tuner? and/or Pre-Selector? David Shortwave 3 December 27th 05 09:59 PM
Single Wire Antenna {Longwire / Random Wire Antenna} - What To Use : Antenna Tuner? and/or Pre-Selector? David Shortwave 0 December 27th 05 09:18 PM
Vincent antenna Allen Windhorn Antenna 3 May 24th 05 12:37 AM


All times are GMT +1. The time now is 04:18 AM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017