I was wondering if anybody out there is using two mobile whip antennas
on top band.
The antenna would have max gain at 90 degrees but it should provide
good local contacts if placed at a height of 70 feet.
If one draws a circle as a radiation fields one could see where
the maximum gain is i.e. 90 degrees.
Now if you draw an antenna field with less than half the gain the
max would still be at 90 degrees but the gain loss at say 15 degrees
is minimul at best.
In my case when modeling my particular dipole I can make tremendous
strides
in efficiency if I attach wires at the end of the dipole that hang
to the ground
But when comparing gain say at 15 degrees horizontal there is no
worthwhile increase in gain ie less than 10% of the difference !
It would appear to me that if you are unable to put in a large area of
a ground system one would do better with shortened dipoles but well
away from ground
Comments
Art

Art Unwin KB9MZ wrote:
In my case when modeling my particular dipole I can make tremendous
strides in efficiency if I attach wires at the end of the dipole that hang
to the ground
But when comparing gain say at 15 degrees horizontal there is no
worthwhile increase in gain ie less than 10% of the difference !

Art, a *gain* in efficiency is as good as an increase in gain. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote in message ...
Art Unwin KB9MZ wrote:
In my case when modeling my particular dipole I can make tremendous
strides in efficiency if I attach wires at the end of the dipole that hang
to the ground
But when comparing gain say at 15 degrees horizontal there is no
worthwhile increase in gain ie less than 10% of the difference !

Art, a *gain* in efficiency is as good as an increase in gain. :-)

Cecil I believe you are missing the point.Either that or you have a
motive for such an answer.
An increase in efficiency will provide an equivalent gain at its 'max
directivity point' but the gain at a low angle has increased by a very
small amount. With my dipole antenna say at 40 % efficiency would be
equivalent to a beverage antenna at 15 degrees.
If I upped the efficiency of my antenna say to 80% then yes, you would
see
the gain at 90 degrees increase in a worth while manner but when you
examine an overlay with the beverage at 15 degrees you would be hard
put to see any difference. Draw the radiation patterns with both
circles meeting at the ground level and you will see what I am getting
at.( I am looking at horisontal polarisation now that provides
different ground losses for polarisation antenna forms , the beverage
being very close to ground)
Art

Art, KB9MZ wrote:
"---it should provide good local contacts if placed at a height of 70
feet."

If back to back mobile antennas are used as a dipole at 70 feet, the
question is: why not use the vertical distance for a radiating
conductor, and the horizontal space to load the too-short vertical?

1/4-wave at 160-meters is about 131 feet.

A vertical mobile antenna is likely limited to about 4 meters and a
dipole made from two is only about 8 meters long. That`s only 10% of
1/2-wavelength. Radiation resistance of such a short dipole will be very
low and capacitive reactance will be very high requiring much reactance
to tune out. This is inherently lossy.

Another disadvantage if the dipole is only about 1/8-wavelength high and
horizontal, will be concentration of most radiation directly overhead.
For local and DX coverage, energy concentration near the horizon is
important. Vertical antennas provide low angle radiation even when they
are short. They have a null directly overhead.

70 feet is 53% of the height required for 1/4-wave resonance at 160
meters, and some of the missing length can be made up by horizontal
loading at the top of the vertical height.

ON4UN`s "Low Band DXing" Chapter 9, "Vertical Antennas" can be very
helpful in choosing a configuration that will work well.

Best regards, Richard Harrison, KB5WZI

Richard
My question was placed at 'two whips to form a dipole'.
It was not a recomendation nor did it call for comparisons
to other designs that may be better.
With that clear I stated that the max radiation will be at 90 degrees
and that I am sure is accepted and will provide local contacts.
Now placing the two whips on top of the tower negates the need for a
ground plane which is no small matter as well as half the max
radiationwill be at
45 degrees. Thus the simple question is anybody using two whips as a
dipole?
I could well imagine a setup of a loaded dipole being a very GOOD
antenna in some instances because of the avoidance of ground losses
with those having a small lot or do not have the facilities for
extensive ground planes.
My dipole is 50% efficient on 160, 90% on 80 which means in each case
for TOA
in the 40 to 50 range they exceed gains for a run of the mill
vertical.
So again Richard I asked for experiences from those using two loaded
verticals made into a dipole for horizontal polarisation on 160M.
Regards
Art







(Richard Harrison) wrote in message ...
Art, KB9MZ wrote:
"---it should provide good local contacts if placed at a height of 70
feet."

If back to back mobile antennas are used as a dipole at 70 feet, the
question is: why not use the vertical distance for a radiating
conductor, and the horizontal space to load the too-short vertical?

1/4-wave at 160-meters is about 131 feet.

A vertical mobile antenna is likely limited to about 4 meters and a
dipole made from two is only about 8 meters long. That`s only 10% of
1/2-wavelength. Radiation resistance of such a short dipole will be very
low and capacitive reactance will be very high requiring much reactance
to tune out. This is inherently lossy.

Another disadvantage if the dipole is only about 1/8-wavelength high and
horizontal, will be concentration of most radiation directly overhead.
For local and DX coverage, energy concentration near the horizon is
important. Vertical antennas provide low angle radiation even when they
are short. They have a null directly overhead.

70 feet is 53% of the height required for 1/4-wave resonance at 160
meters, and some of the missing length can be made up by horizontal
loading at the top of the vertical height.

ON4UN`s "Low Band DXing" Chapter 9, "Vertical Antennas" can be very
helpful in choosing a configuration that will work well.

Best regards, Richard Harrison, KB5WZI

Art, KB9MZ wrote:
"It was not a recommendation nor did it call for comparisons to other
designs that may be better."

Art is correct. Vertical antennas require radials to avoid ground loss.
Norizontal dipole radiation in free-space is perpendicular to the
antenna.

Art also asks: Is anybody using two whips as a dipole?

I`m sure they are. Saw a hamfest vendor selling loaded whips and mounts
designed to mount two of them as a dipole. There have been discussions
in previous threads about this application. Hope there are new responses
to Art`s question.

Best regards, Richard Harrison, KB5WZI

On 4 Dec 2003 08:42:58 -0800, (Art Unwin KB9MZ)
wrote:

I asked for experiences from those using two loaded
verticals made into a dipole for horizontal polarisation on 160M.
Regards
Art

Hi Art,

Miserable. A simple balloon lifted halfwave vertical was declared the
big guns by a net (surpassing their own antennas).

Richard was right, more signal would find its way out if you simply
drove the coax shield running up to the "dipole."

73's
Richard Clark, KB7QHC

Exactly
The ground influence on verticals is horible so getting
away from it or going horizontal are good viable choices
depending on the TOA required for your own particular purposes
Art


Richard Clark wrote in message . ..
On 4 Dec 2003 08:42:58 -0800, (Art Unwin KB9MZ)
wrote:

I asked for experiences from those using two loaded
verticals made into a dipole for horizontal polarisation on 160M.
Regards
Art

Hi Art,

Miserable. A simple balloon lifted halfwave vertical was declared the
big guns by a net (surpassing their own antennas).

Richard was right, more signal would find its way out if you simply
drove the coax shield running up to the "dipole."

73's
Richard Clark, KB7QHC

On 5 Dec 2003 06:08:46 -0800, (Art Unwin KB9MZ)
wrote:

Exactly
The ground influence on verticals is horible so getting
away from it or going horizontal are good viable choices
depending on the TOA required for your own particular purposes
Art

Hi Art,

You really need to read posts before "agreeing" with them.

73's
Richard Clark, KB7QHC


Richard Clark wrote in message . ..
On 4 Dec 2003 08:42:58 -0800, (Art Unwin KB9MZ)
wrote:

I asked for experiences from those using two loaded
verticals made into a dipole for horizontal polarisation on 160M.
Regards
Art

Hi Art,

Miserable. A simple balloon lifted halfwave vertical was declared the
big guns by a net (surpassing their own antennas).

Richard was right, more signal would find its way out if you simply
drove the coax shield running up to the "dipole."

73's
Richard Clark, KB7QHC