"aunwin" wrote in message
news:aqK1c.176934$jk2.646180@attbi_s53...
Why must only series circuits be considered for radiators?.

The last discription I saw of a quarter wavw antenna was that of a paralell
circuit. Isnt that basically how a capacity hat shortens an antenna, by
increasing the paralell capacitance

What is it about parallel circuits that make them
unsuitable?

Who says they are not.


Is stagger tuning a parallel circuit ?

This question being out of context with the other questions seems to
indicate you really dont know what stagger tuning means so I dont know how
to reply.

Regards
Art

Jimmy wrote:
"The last description I saw of a quarter wave antenna was that of a
parallel circuit. Isn`t that basically how a capacity hat shortens an
antenna, by increasing the parallel capacitance?"

Parallel or series hardly makes any difference.

The 1/4-wave antenna is essentially a 1/2-wave antenna with the missing
1/4-wave piece replaced by a ground reflection. Terman illustrates
current distribution in a doublet on page 866 of his 1955 edition. He
says:
"These current distributions are those that would be obtained by
applying the exciting voltage in series with the wire at a current loop,
or to one end of the wire."

The series representation is conventional and comes from the distributed
nature of resistance, inductance, and capacitance along the antenna
wire.

From the generator or transmission line`s point of view, it may be more
convenient to view the antenna load as a parallel resonant circuit.
Parallel or series circuit, they are mathematically interchangeable by
using conversion formulas which appear in various books including the
ARRL Antenna Book. Use whichever form you like.

There is a difference between a length of wire and a tank circuit. The
wire has multiple harmonically related resonances. The tank circuit does
not. It has only one resonance.

Jimmy also wrote:
"Who says they are not (parallel circuits suitable to model an
antenna)?"

Yes, Art Unwin, who says they are not?

Jimmy also wrote:
"This question (is stagger tuning a parallel circuit?) being out of
context with the other questions seems to indicate you really don`t know
what stagger tuning means so I don`t know how to reply."

Art for years has hijacked threads to advertise a tuned loop conjoined
with a dipole. One of his claims is that the loop is tuned to one
frequency and the dipole is tuned to a different frequency ergo a
broadband antenna is produced. You must guess between the lines to make
sense of what Art says.

Best regards, Richard Harrison, KB5WZI

On Sun, 7 Mar 2004 21:18:46 -0600 (CST),
(Richard Harrison) wrote:

Jimmy wrote:
"The last description I saw of a quarter wave antenna was that of a
parallel circuit. Isn`t that basically how a capacity hat shortens an
antenna, by increasing the parallel capacitance?"

Parallel or series hardly makes any difference.

Part of this debate has ignored that all resonant circuits can be
analyzed as both parallel and series. That is, barring your and my
observations.

To force the parallel resonant observation upon the quarterwave
vertical, all that need be done is to move the drive from the base to
the tip. The same current distribution will be observed, the same
radiation characteristic will persist, and as such nothing has really
changed.

This may raise hosannas from Art in that he has been redeemed by this
move - but at a cost. Moving that drive to that point necessarily
brings a lead that is a quarterwave long to accomplish this mission.
We then find ourselves in a situation where the solution has become
part of the problem. Do we really have a drive at the top, or another
radiator? Art, I am sure, would dismiss this necessary lead as "not
part of the antenna" and would close the books before the audit is
complete. It would be in fact the classic folded dipole. To escape
that and maintain the mystery of driving from the top, we would have
to accept unipolar RF sources (soon to be patented).

However, if we were to return to Jimmy's question/observation of the
top hat; that structure resides at the point we speculatively drove
(the distal tip), and with respect to its own contribution looking
back towards ground, it sees an entirely different circuit topology
than does the drive at the base. This is not exactly the same
situation as moving the drive. The top hat does not grace a full
quarterwave vertical as it would be redundant to that mission. Such
an addition would end up instead throwing the design into a quasi
3/8ths tuning, or such, to dubious purpose. Thus the analysis becomes
murky (for further debate suitable to efficiency per unit length). We
can shorten the quarterwave by small intervals and find the top hat
appears to replace that missing length; but as we shorten, the system
becomes capacitively reactive and we hardly need more.

One of the language problems with the name Capacity Top Hat, and the
expectation of adding more capacitance is that the short antenna is
already excessively capacitive. Logically, the addition of more
capacity does not lead to resonance. The purpose of a top hat
transcends notions of resonance to answer problems of radiation
characteristics. Resonance, as always, is answered through other
devices (inductors) that reside there to serve that same problem of
radiation.

After 10 years of reading a spectrum of discussion, I have never,
ever, read any post that purported a mission to build a 100pf top hat.
I have never read anyone ask how big a hat was needed to resonate
such-and-such inductance. The structure is often too big to qualify
as a lumped capacitor and calling it by this name is a convention, not
a reality.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
One of the language problems with the name Capacity Top Hat, and the
expectation of adding more capacitance is that the short antenna is
already excessively capacitive. Logically, the addition of more
capacity does not lead to resonance.

Yet, we can usually add enough top hat metal to bring the antenna
system to resonance. Must be your uncertainty principle at work. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Clark wrote:
"One of the language problems with the name Capacity Top Hat, and the
expectation of adding more capacitance is that the short antenna is
already excessively capacitive."

Yes, but that is an incomplete description. The short antenna has an
excess of capacitive REACTANCE. It can be tuned to resonance by
increasing the capacitance between its ends.

Best regards, Richard Harrison, KB5WZI

Richard Clark, KB7QHC:

Part of this debate has ignored that all resonant circuits can be
analyzed as both parallel and series. That is, barring your and my
observations.

To force the parallel resonant observation upon the quarterwave
vertical, all that need be done is to move the drive from the base to
the tip. The same current distribution will be observed, the same
radiation characteristic will persist, and as such nothing has really
changed.


Uh, huh, NOT!

The top hat does not grace a full
quarterwave vertical as it would be redundant to that mission. Such
an addition would end up instead throwing the design into a quasi
3/8ths tuning, or such, to dubious purpose.

Uh, huh.
Quasi 3/8 tuning (with 1/8 radials) provides 50 ohm impedance, no need for
matching junk, lowers tha angle and provides increase in gain. Dubious? Not to
me.

Logically, the addition of more
capacity does not lead to resonance.

Oh no?

Yuri, K3BU

On 13 Mar 2004 14:09:45 GMT, oUsama (Yuri Blanarovich)
wrote:
Logically, the addition of more
capacity does not lead to resonance.

Oh no?

Ah, such a bonus round!

How many pF capacitance in your top hat? :-)

73's
Richard Clark, KB7QHC