In another post, those of us from THIS side of the pond were
shown the Texas Bugcatcher antenna (easily googled), and its
extensive website.

It would seem to be a universal panacea for those with small
gardens, subject to the availability of a ground plane.

It discusses capacity hats. And my question is this, why is it called
a capacity hat, because calculation of the capacity between the hat
and the ground will only give, at a guess, a miniscule fraction of a puff.

My reasoning is that because the waves spread out in all directions
in the hat, then there is no, or very little, radiation from the hat because
of field cancellation, but when the waves all return simultaneously to the
main element, they have incurred a phase change that you'd get had there
been a capacitor in circuit?

(Always willing to learn more, and to be corrected if my thought
experiment has gone up a blind alley, or in this case, a capacity hat
alley!)

On Thursday, February 13, 2014 4:09:53 AM UTC-6, gareth wrote:

My reasoning is that because the waves spread out in all directions

in the hat, then there is no, or very little, radiation from the hat because

of field cancellation, but when the waves all return simultaneously to the

main element, they have incurred a phase change that you'd get had there

been a capacitor in circuit?



(Always willing to learn more, and to be corrected if my thought

experiment has gone up a blind alley, or in this case, a capacity hat

alley!)

The use of the hat has two main purposes.

#1, it will reduce the number of turns needed with the loading
coil, assuming the whip is shorter than 1/4 wave including the
hat.

#2, and probably most important. It improves the current
distribution through the length of the whip and makes the current
distribution a good bit more linear from the base to the tip.

I don't use one myself, because they catch a lot of wind, and
they look ugly on a vehicle. :/
I compromise by mounting the loading coil as high as possible,
which also helps current distribution.

wrote in message
...
On Thursday, February 13, 2014 4:09:53 AM UTC-6, gareth wrote:
My reasoning is that because the waves spread out in all directions
in the hat, then there is no, or very little, radiation from the hat
because
of field cancellation, but when the waves all return simultaneously to
the
main element, they have incurred a phase change that you'd get had there
been a capacitor in circuit?

(Always willing to learn more, and to be corrected if my thought
experiment has gone up a blind alley, or in this case, a capacity hat
alley!)

The use of the hat has two main purposes.
#1, it will reduce the number of turns needed with the loading
coil, assuming the whip is shorter than 1/4 wave including the
hat.
#2, and probably most important. It improves the current
distribution through the length of the whip and makes the current
distribution a good bit more linear from the base to the tip.
I don't use one myself, because they catch a lot of wind, and
they look ugly on a vehicle. :/
I compromise by mounting the loading coil as high as possible,
which also helps current distribution.

Yes, all very well, and not disputed, but I was interested in a
discussion of how it actually works at the physics level?

On Thursday, February 13, 2014 4:44:04 AM UTC-6, gareth wrote:
I was interested in a
discussion of how it actually works at the physics level?

The capacitance to ground concept is necessary if the lumped circuit model is being used. When one starts talking about phase shifts, one needs to change over to the distributed network (wave reflection) model. An HF mobile antenna is usually 90 degrees long electrically. The following paper indicates that if phase is important, the distributed network model should be used for anything electrically longer than 15 degrees.

http://hamwaves.com/antennas/inductance/corum.pdf

Capacitance to ground and a phase shift due to reflections from the end of a top hat are incompatible concepts from two different math models. The distributed network model is closer to Maxwell's equations than is the lumped circuit model.

On Thursday, February 13, 2014 4:44:04 AM UTC-6, gareth wrote:
wrote in message

...

On Thursday, February 13, 2014 4:09:53 AM UTC-6, gareth wrote:

My reasoning is that because the waves spread out in all directions

in the hat, then there is no, or very little, radiation from the hat

because

of field cancellation, but when the waves all return simultaneously to

the

main element, they have incurred a phase change that you'd get had there

been a capacitor in circuit?



(Always willing to learn more, and to be corrected if my thought

experiment has gone up a blind alley, or in this case, a capacity hat

alley!)



The use of the hat has two main purposes.

#1, it will reduce the number of turns needed with the loading

coil, assuming the whip is shorter than 1/4 wave including the

hat.

#2, and probably most important. It improves the current

distribution through the length of the whip and makes the current

distribution a good bit more linear from the base to the tip.

I don't use one myself, because they catch a lot of wind, and

they look ugly on a vehicle. :/

I compromise by mounting the loading coil as high as possible,

which also helps current distribution.



Yes, all very well, and not disputed, but I was interested in a

discussion of how it actually works at the physics level?

You are better off with the proper textbooks, than reading my
jibber jabber. That's what I use when I want to brush up on
how something works at the physics level. :|
I read the various books. I don't trust too many on the interweb,
as many will lead you astray with jibber jabber and gibberish.

Then, if you have a problem with something in the various textbooks,
you can come back and argue it on the interweb.

"gareth" wrote in message
...
In another post, those of us from THIS side of the pond were
shown the Texas Bugcatcher antenna (easily googled), and its
extensive website.

And my question is this, why is it called
a capacity hat, because calculation of the capacity between the hat
and the ground will only give, at a guess, a miniscule fraction of a puff.


Others have provided essential theory.

In practice: http://en.wikipedia.org/wiki/KFI
See paragraph entitled "Third Tower" and read
second sentence.

75 feet of broadcast tower is a lot of steel and a
fair amount of money.

Pictures of the tower and hat are at
http://www.oldradio.com/archives/warstories/640.htm
and scroll down most of the way.

In article ,
Sal salmonella@food poisoning.org wrote:

"gareth" wrote in message
...

In another post, those of us from THIS side of the pond were
shown the Texas Bugcatcher antenna (easily googled), and its
extensive website.

And my question is this, why is it called
a capacity hat, because calculation of the capacity between the hat
and the ground will only give, at a guess, a miniscule fraction of a puff.


Others have provided essential theory.

In practice: http://en.wikipedia.org/wiki/KFI
See paragraph entitled "Third Tower" and read
second sentence.

Another interesting "in practice" writeup can be found in the first 50
pages of Ed Laport's excellent "Radio Antenna Engineering", where he
discusses the use of top-loading of low-frequency broadcast antennas.

http://snulbug.mtview.ca.us/books/Ra...naEngineering/

wrote in message
...

You are better off with the proper textbooks, than reading my
jibber jabber.

My attempt to re-awaken discussion on Usenet, if only because
uk.radio.amateur is currently under threat of closure, strangely,
because of the behaviour of those who want it closed.

"Sal" salmonella@food poisoning.org wrote in message
...
"gareth" wrote in message
...
In another post, those of us from THIS side of the pond were
shown the Texas Bugcatcher antenna (easily googled), and its
extensive website.
And my question is this, why is it called
a capacity hat, because calculation of the capacity between the hat
and the ground will only give, at a guess, a miniscule fraction of a
puff.
Others have provided essential theory.
In practice: http://en.wikipedia.org/wiki/KFI
See paragraph entitled "Third Tower" and read
second sentence.
75 feet of broadcast tower is a lot of steel and a
fair amount of money.
Pictures of the tower and hat are at
http://www.oldradio.com/archives/warstories/640.htm
and scroll down most of the way.

Thanks, but I do not pursue URLS, my viewpoint being
that if there is something worthwhile to discuss, then
discuss it.

On 14/02/2014 09:48, gareth wrote:
"Sal" salmonella@food poisoning.org wrote in message
...
"gareth" wrote in message
...
In another post, those of us from THIS side of the pond were
shown the Texas Bugcatcher antenna (easily googled), and its
extensive website.
And my question is this, why is it called
a capacity hat, because calculation of the capacity between the hat
and the ground will only give, at a guess, a miniscule fraction of a
puff.
Others have provided essential theory.
In practice: http://en.wikipedia.org/wiki/KFI
See paragraph entitled "Third Tower" and read
second sentence.
75 feet of broadcast tower is a lot of steel and a
fair amount of money.
Pictures of the tower and hat are at
http://www.oldradio.com/archives/warstories/640.htm
and scroll down most of the way.

Thanks, but I do not pursue URLS, my viewpoint being
that if there is something worthwhile to discuss, then
discuss it.

The latter link is a series of photographs. Are you saying you need
somebody to describe them for you?