Art, KB9MZ wrote:
"Taking this point further, one wonders why inductors in the real world
are not designed to be a point load, albeit in a two dimensional world."

Seems we exhausted this topic some time ago. The ends of a coil do not
have to be 180-degrees out of phase due to the configuration and
composition of connections external to the coil. Waves traveling in
opposite directions through the coil can produce a standing wave within
the coil regardless of coil position. Energy into one end of a coil does
not necessarily equal energy out because radiation and conversion to
heat may not be uniform throughout the coil.

Nevertheless, I`m elated. I`ve found my copy of Terman`s "Electronic and
Radio Engineering".
On page 11, Terman says:
"Inductance in microhenrys = (F)(nsquared)(d)
n = number of turns
d = diameter of coil measured to center of wires
F = constant that depends only upon the ratio of length to diameter,
given in Fig 2.2"

The inductance formula above is for a single-layer solenoid. The
footnote says:
"A comprehensive collection of such formulas is given by F.E. Terman,
"Radio Engineers` Handbook" pp 48-64, McGraw-Hill Book Company, Inc.,
New York, 1943."

On pages 59 and 60 of Terman`s "Handbook" he treats a "Flat Retangular
Coil". He gives a formula (47) for its inductance, which is complicated
by multiple dimensions, length, width, etc. Inductance is nevertheless
proportional to the square of the number of turns as in the case of a
solenoid.

My Terman`s Handbook is difficult for me to read due to its damage in a
flood a few years ago. Its pages are stuck together and torn, but it`s
worth trying to use.

Doubts about radiation from shortened antennas can be resolved by
reference to "Terman`s "Radio Engineers` Handbook". On page 795 Terman
says:
"Top loading has the same effect on field distribution in a vertical
plane as a greater height."

Terman also says of a loading coil inserted in an antenna a little way
down from the top:
"This method of top loading gives results equivalent to those obtained
with a capacity top."

Maybe a flat coil is more equal than a solenoid. Were it of great
importance, Terman would have told us.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote,

Maybe a flat coil is more equal than a solenoid. Were it of great
importance, Terman would have told us.


A flat coil should work fine as a capacitance hat.
73,
Tom Donaly, KA6RUH

A flat coil should work fine as a capacitance hat.

I have thought about trying this. With a spiral or flat coil you have a hat
and a loading coil all rolled up in one. Winding spiral coils is not easy, and
the mechanics of mounting on my mobile antenna have kept me from trying, but I
may yet. What do you think Tom?
73 Gary N4AST

Gary wrote,

A flat coil should work fine as a capacitance hat.

I have thought about trying this. With a spiral or flat coil you have a hat
and a loading coil all rolled up in one. Winding spiral coils is not easy,
and
the mechanics of mounting on my mobile antenna have kept me from trying, but
I
may yet. What do you think Tom?
73 Gary N4AST


Hi Gary,
it may not be worth all the work involved. I'm not an expert on
mobile antennas, so don't take anything I write on the subject too seriously.
On the other hand, there should be some current into the coil causing a
changing charge density at the other end which would, in turn, cause a
changing electric field in the vicinity of the antenna, which would cause
electromagnetic radiation, so you might see some improvement over
what you're using now, after all.
Try it out.
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
On the other hand, there should be some current into the coil causing a
changing charge density at the other end which would, in turn, cause a
changing electric field in the vicinity of the antenna, which would cause
electromagnetic radiation, so you might see some improvement over
what you're using now, after all.

If the pancake coil is in the horizontal plane, it will probably
radiate horizontally polarized radiation and probably straight up.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Tdonaly wrote:
On the other hand, there should be some current into the coil causing a
changing charge density at the other end which would, in turn, cause a
changing electric field in the vicinity of the antenna, which would cause
electromagnetic radiation, so you might see some improvement over
what you're using now, after all.

If the pancake coil is in the horizontal plane, it will probably
radiate horizontally polarized radiation and probably straight up.
--
73, Cecil http://www.qsl.net/w5dxp



It might. Do you want to tell us why you think so, Cecil?
73,
Tom Donaly

Tdonaly wrote:
Cecil wrote,
If the pancake coil is in the horizontal plane, it will probably
radiate horizontally polarized radiation and probably straight up.

It might. Do you want to tell us why you think so, Cecil?

Just off the top of my head - since the coil exists essentially only
in the horizontal plane, the radiation from the coil is likely to be
horizontal. If it is mobile, it is a very low antenna. Very low
horizontal radiation usually tends to result in an NVIS radiation
pattern in the far field. Hope there are no bugs in that logic.
--
73, Cecil http://www.qsl.net/w5dxp



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JGBOYLES wrote:
With a spiral or flat coil you have a hat
and a loading coil all rolled up in one. Winding spiral coils is not easy, and
the mechanics of mounting on my mobile antenna have kept me from trying, but I
may yet.

There was a magazine article a couple of years ago about such
in one of the ham rags - sorry, don't remember which one.
--
73, Cecil http://www.qsl.net/w5dxp



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Pancakes have been written about for a while in RADCOM of the U.K.
In Europe there is some experimenting going on below the
broadcast band but it is limited to a few watts.
The basket weave was mainly introduced to REMOVE the
intercapacitance of the coils and a capacity hat was
introduced immediately AFTER the inductor.
Because they were only using a few watts there was not a concern
regarding voltage breakdown, a concern that should be reviewed before
entertaining the idea at the end of a high powered whip !
Regards
Art



Cecil Moore wrote in message ...
JGBOYLES wrote:
With a spiral or flat coil you have a hat
and a loading coil all rolled up in one. Winding spiral coils is not easy, and
the mechanics of mounting on my mobile antenna have kept me from trying, but I
may yet.

There was a magazine article a couple of years ago about such
in one of the ham rags - sorry, don't remember which one.