" bravely wrote to "All" (23 Mar 05 15:13:22)
--- on the heady topic of " Loading Coil Q"

nm It's the best option. And top loading is best using capacitive
nm loading, where as if using a coil for top loading, the coil losses
nm overshadow any increase in efficiency from the improved current
nm distribution, etc.. Top loading using wires is the best system you
nm could use, if you can swing it.

How about distributed loading?

A*s*i*m*o*v

.... May you find the light and walk the mountain tops.

On Wednesday, 23 Mar 2005 22:30:32 -500, "Asimov"
wrote:

How about distributed loading?

Hi OM,

The wrong way, and it is called air cooled resistance. If you simply
did a Googles group search using that very query, you would find a
trove of hits.

73's
Richard Clark, KB7QHC

Asimov wrote:
How about distributed loading?

Helical antennas are not as efficient as
other forms of loading.
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" bravely wrote to "All" (24 Mar 05 09:19:15)
--- on the heady topic of " Loading Coil Q"

CM From: Cecil Moore
CM Xref: aeinews rec.radio.amateur.antenna:27211

CM Helical antennas are not as efficient as
CM other forms of loading.

Considering that sometimes efficiency isn't quite as important, like
for example reception, are helical antennas less used simply because
the math is a little harder or not discussed enough? I recall seeing
this type being popularized during the old CB craze in the mid 70's.

A*s*i*m*o*v

.... "Ol' Frothinslosh": The pale, stale ale with the foam on the bottom.

Asimov wrote:
"Cecil Moore" wrote:
CM Helical antennas are not as efficient as
CM other forms of loading.

Considering that sometimes efficiency isn't quite as important, like
for example reception, are helical antennas less used simply because
the math is a little harder or not discussed enough?

Probably a collection of reasons. A high-Q loading coil in
the center of a vertical is much more efficient than spreading
the loading out over the entire antenna. Helical antennas are
hard to wind and are generally wound on PVC pipe which also
reduces efficiency and increases wind load. Even more efficiency
is lost without a good ground plane. If one doesn't compromise
on the ground plane, why compromise on the antenna? Most of us
old timers have tried helicals and given up on them - lots of
effort to achieve a poor performance.
--
73, Cecil http://www.qsl.net/w5dxp

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"Cecil Moore" wrote
A high-Q loading coil in
the center of a vertical is much more efficient than spreading
the loading out over the entire antenna.

============================

Wrong! Spreading a multi-turn coil allows a MUCH thicker wire
diameter to be used with spaced turns. Also the coil diameter can be
increased to minimise the number of turns.

Result : higher coil Q, lower coil loss, greater efficiency.
----
Reg.

Reg Edwards wrote:

"Cecil Moore" wrote

A high-Q loading coil in
the center of a vertical is much more efficient than spreading
the loading out over the entire antenna.

Wrong! Spreading a multi-turn coil allows a MUCH thicker wire
diameter to be used with spaced turns. Also the coil diameter can be
increased to minimise the number of turns.

Result : higher coil Q, lower coil loss, greater efficiency.

Got to disagree with you on that one, Reg. Mobile shootout
field strength measurements put all the helicals, no matter
what wire diameters were used, considerably down from the
well-designed bugcatchers and screwdrivers. That meter of
wire in each turn of the helical has more resistance than
the centimeter of radiating bottom section that it replaces
at the feedpoint.

It is well known and accepted that moving the mobile loading
coil from the center of the antenna to the base will reduce
the efficiency even though the inductance required for loading
is decreased. With a helical, part of the loading coil is
at the base and that's simply a bad idea when efficiency
is important.

One mobile, in particular, should have performed well. It
was made from 1/4 inch copper tubing with a large diameter
and proper spacing between turns but it was about equal to
a Hustler and considerably down from the top performer which
was top-loaded.

What wins the mobile shootouts is the longest possible straight
bottom section under the coil where the highest current occurs.
That maximum current occurs all up and down that straight bottom
section when a good top hat is added to the antenna. I once won
the shootout competition by putting all the loading (coil+top-hat)
at the top of the antenna using cheap stuff from my junk box.

If one wants to win a mobile shootout, one cannot afford to
install a helical coil at the maximum current section.
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" wrote in message
...
Reg Edwards wrote:

"Cecil Moore" wrote

A high-Q loading coil in
the center of a vertical is much more efficient than spreading
the loading out over the entire antenna.

Wrong! Spreading a multi-turn coil allows a MUCH thicker wire
diameter to be used with spaced turns. Also the coil diameter can
be
increased to minimise the number of turns.

Result : higher coil Q, lower coil loss, greater efficiency.

Got to disagree with you on that one, Reg. Mobile shootout
field strength measurements put all the helicals, no matter
what wire diameters were used, considerably down from the
well-designed bugcatchers and screwdrivers. That meter of
wire in each turn of the helical has more resistance than
the centimeter of radiating bottom section that it replaces
at the feedpoint.

It is well known and accepted that moving the mobile loading
coil from the center of the antenna to the base will reduce
the efficiency even though the inductance required for loading
is decreased. With a helical, part of the loading coil is
at the base and that's simply a bad idea when efficiency
is important.

One mobile, in particular, should have performed well. It
was made from 1/4 inch copper tubing with a large diameter
and proper spacing between turns but it was about equal to
a Hustler and considerably down from the top performer which
was top-loaded.

What wins the mobile shootouts is the longest possible straight
bottom section under the coil where the highest current occurs.
That maximum current occurs all up and down that straight bottom
section when a good top hat is added to the antenna. I once won
the shootout competition by putting all the loading (coil+top-hat)
at the top of the antenna using cheap stuff from my junk box.

If one wants to win a mobile shootout, one cannot afford to
install a helical coil at the maximum current section.
--
==================================

Cec,

(1) A mobile antenna is NOT a 1/4-wave resonant, base-fed,
ground-mounted loaded vertical which behaves reasonably predictable.

(2) A mobile antenna is a relatively-isolated-from-ground, 1/2-wave
resonant, loaded, off-centre-fed vertical dipole which defies rational
analysis.

(3) It is impossible to separate the many different behaviour modes
and effects, differentiate between them and allocate relative
magnitudes. One has to be careful to control one's imagination when
describing effects.

I've never seen one near to, but I understand "screwdriver" type
mobile antennas are akin to long helicals specially at the lowest
operating frequency.
----
Reg.