I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I
have enough of the first two to create a pole of about 15 feet each
and about 8 to 9 feet with the 1/5 inch poles. The poles are no more
than 4 feet long each, but they are able to tuck inside each other, at
least for the same diameter.

What I want to do is to make up a 'kit' with these that I can take to
the field to setup whatever antenna I want to use at the time. For
example, I might set it up as a 20 meter vertical in one
configuration, but in the evening, I might reconfigure it to 75 meters
or 15, or 30 or whatever I desire.

One consideration is to create a high-q coil for it. I am thinking of
using 1/4 inch copper tubing to make a ten to twelve inch diameter
coil so I can match it to the lower bands. I have been reading that
base loaded coils have to be matched to the antenna, but center loaded
verticals are more closely matched to 50 ohms. from what I have been
reading, the center loaded coil requires more turns and a top loaded
coil even more.

A capacity hat is also a viable option.

I am wondering how much I am helping or hurting myself with the larger
coil or if I would be better off with a smaller coil. One thought is
to connect x number of poles, then the coil, then another set of poles
or a whip to make the final adjustment for the match or to match the
antenna by tapping the coil.

I am open to all suggestions, but I am interested in knowing the best
location for the coil and the best size for it.

Thank you

--
73 for now
Buck
N4PGW

Program LOADCOIL models short, coil-loaded, vertical antennas.

Amongst other things it allows the coil to slide up and down the
antenna (from the keyboard) and find the coil location at which power
radiating efficiency is maximised.

The best location depends on antenna dimensions, coil dimensions and
ground loss resistance ohms, and is very non-critical. Top loading is
never the best.

Download program LOADCOIL in a few seconds from website below and run
immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Buck wrote:
I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I
have enough of the first two to create a pole of about 15 feet each
and about 8 to 9 feet with the 1/5 inch poles. The poles are no more
than 4 feet long each, but they are able to tuck inside each other,
at
least for the same diameter.

What I want to do is to make up a 'kit' with these that I can take to
the field to setup whatever antenna I want to use at the time. For
example, I might set it up as a 20 meter vertical in one
configuration, but in the evening, I might reconfigure it to 75
meters
or 15, or 30 or whatever I desire.

One consideration is to create a high-q coil for it. I am thinking
of
using 1/4 inch copper tubing to make a ten to twelve inch diameter
coil so I can match it to the lower bands.

That thickness of coil is overkill....

I have been reading that
base loaded coils have to be matched to the antenna, but center
loaded
verticals are more closely matched to 50 ohms.

The loading coil is used to tune out the capacitive reactance.
The input impedance will vary to length of the vertical, coil loss,
ground loss, etc..Just because a center load is used, doesn't always
mean the input impedance will end up 50 ohms..

from what I have been
reading, the center loaded coil requires more turns and a top loaded
coil even more.

Yes.

A capacity hat is also a viable option.

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

I am wondering how much I am helping or hurting myself with the
larger
coil or if I would be better off with a smaller coil.

It's not that critical...

One thought is
to connect x number of poles, then the coil, then another set of
poles
or a whip to make the final adjustment for the match or to match the
antenna by tapping the coil.

I am open to all suggestions, but I am interested in knowing the best
location for the coil and the best size for it.

The *best* location for a loading coil is appx 2/3 to 3/4 up the
radiator. But even half way up is fine. Base loading is the least
efficient, and has the worst current distribution. But it uses the
least number of coil turns, and would have the least coil loss.
Being low, it's the easiest to adjust also...
Don't forget that the ground system for a short loaded vertical,
becomes even more critical than for a full 1/4 wave vertical.
It's for this reason that I usually avoid verticals for portable
use, unless the ground issue can be dealt with. IE: at the beach
is a good place for verticals...But in the boonies, on lossy, rocky,
ground, they may not do so hot if you have no radials. In that
case, I would take the vertical "sticks", and hang a dipole from
them...:/ My mobile antenna is my usual "portable vertical"...MK

" 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

Reg Edwards wrote:
Amongst other things it allows the coil to slide up and down the
antenna (from the keyboard) and find the coil location at which power
radiating efficiency is maximised.

Sliding the coil up and down the antenna also changes
the resonant frequency.
--
73, Cecil http://www.qsl.net/w5dxp


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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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Thank you to Cecil, Reg, Mark, Asimov and Richard.

I have read what you said and done more reading about Cap Hats. The
Cap Hat doesn't improve the inductor, it basically replaces it, at
least in part, which removes the loss of the inductor. I
misunderstood that somehow.

What I will focus on, then, is to create some form of capacity hat for
each appropriate band together with an adjustable vertical length for
tuning to the appropriate frequency.

Mark, You may have a point about the dipole being better, especially
for portable operation. I just want to experiment with the aluminum
poles I have. I may take your advice and use them to create a
portable tower in the long-run. But first I think I will try out the
vertical.

Thanks to all,

Buck
N4PGW


On Wed, 23 Mar 2005 12:56:34 -0500, Buck wrote:


I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I
have enough of the first two to create a pole of about 15 feet each
and about 8 to 9 feet with the 1/5 inch poles. The poles are no more
than 4 feet long each, but they are able to tuck inside each other, at
least for the same diameter.

What I want to do is to make up a 'kit' with these that I can take to
the field to setup whatever antenna I want to use at the time. For
example, I might set it up as a 20 meter vertical in one
configuration, but in the evening, I might reconfigure it to 75 meters
or 15, or 30 or whatever I desire.

One consideration is to create a high-q coil for it. I am thinking of
using 1/4 inch copper tubing to make a ten to twelve inch diameter
coil so I can match it to the lower bands. I have been reading that
base loaded coils have to be matched to the antenna, but center loaded
verticals are more closely matched to 50 ohms. from what I have been
reading, the center loaded coil requires more turns and a top loaded
coil even more.

A capacity hat is also a viable option.

I am wondering how much I am helping or hurting myself with the larger
coil or if I would be better off with a smaller coil. One thought is
to connect x number of poles, then the coil, then another set of poles
or a whip to make the final adjustment for the match or to match the
antenna by tapping the coil.

I am open to all suggestions, but I am interested in knowing the best
location for the coil and the best size for it.

Thank you

--
73 for now
Buck
N4PGW

Mark, You may have a point about the dipole being better, especially
for portable operation. I just want to experiment with the aluminum
poles I have. I may take your advice and use them to create a
portable tower in the long-run. But first I think I will try out the
vertical.

You could probably rig it up to do either, if the vertical
is stout enough to support a dipole/s. I have a couple of
drive on masts that I use with the fence rail masting.
Two of those makes 20 ft, and a good support for dipoles,
or other antennas. For industrial use, I have a tower and
beam I can drag around...I've drug it to the last four field
days...Wonder if I'm gonna make it five..?? It's a lot of
work for a two day deal....:/ I'm almost tempted to take a
field day vacation for a year...Have to see...MK

"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.