I agree as well, a properly engineered single 102"
will outperform duals anyday.
Most truckers don't understand how and why antennas radiate RF energy and
they run duals because they give a balanced look, as a bonus co-phased
antennas tend to
supplement each other on vehicles with plastic or fiberglass bodies.
The fact is that the trailer blocks a majority of the RF
that co-phased antennas provide to the rear so they end up with a system
that transceives mainly to the front.
The exception to the rule would be a flatbed trailer.
I use a 102" whip on my T2000 which is mounted to a flat bar attached to the
frame that extends past the edge of the trailer which allows the antenna to
"see" behind the trailer.
The antenna is supported roughly 6' above the mounting point using a custom
made plexiglass bracket.
I have also attached 2 braided steel cables to frame which drag the road
during travel and supply a make-shift earth
ground when parked.
I will be flat honest with you and say that this system gets out farther
then i care for sometimes.
It also works well for sky-wave propagation when conditions permit.
My 4x4 truck uses a pedestal mount 102" whip and a
24" x 24" sheet of stainless, the pedestal is mounted to the floor of the
bed 1.5' behind the cab and cut to length with the top of the bed, the
stainless heet is sandwiched between the top of the pedestal and the bottom
of the antenna.
Very powerful system using a highly tuned 25 LTD
--
Mad-Dog



"Frank Gilliland" wrote in message
...
In , "Leland C. Scott"
wrote:


"Landshark" wrote in message
om...
That all depends on your goals. The typical dual antenna setup, when
done
right, generates maximum signal strength to the front and to the
rear.
The
signal strength to the left and right is considerably reduced. The
same
applies to your receive signal strength as well.


Um, sorry wrong Leland, it makes the signal more omnidirectional.

If done correctly, spaced - phased - good ground plane, it works as I
described.

http://www.bellscb.com/cb_radio_hobb.../antarray.html



Long hual truckers normaly are concerned with communicating with
other
truckers on the road. Those truckers are going to be either in front
or
behind them on the highway. Thus it makes sense to maximize the
signal
in
those directions, and thus the popularity of the setup.

If your more interested in general communications in any direction
then
you
really don't want a dual antenna setup. What you want is an antenna
location
near the center of the truck, which will as nearly as possible, give
you
a
uniform signal in all directions. The site you picked, on the tool
box,
would be a good one.


Again, wrong Leland.

No. The site above has not only a discussion about antenna patterns, but
the
antenna field pattern plots to prove it. I can supply some EZNEC 4.0
simulation files to prove same if you want.


Everyone will think I'm insane for saying this, but Landshark has it
right. In order for co-phased antennas to achieve that ideal figure-8
pattern they must be nearly ideal antennas, which CB antennas are not.
Landshark's link explains why this happens. I wouldn't expect any
significant improvement in the omnidirectional characteristics of
dualies (as the site claims), but I do know they don't provide any
noticable directional gain.






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From: (Mad=A0Dog)
I agree as well, a properly engineered single


102" will outperform duals anyday.


Most truckers don't understand how and why


antennas radiate RF energy and they run


duals because they give a balanced look, as a

bonus co-phased antennas tend to


supplement each other on vehicles with plastic

or fiberglass bodies. The fact is that the trailer


blocks a majority of the RF that co-phased


antennas provide to the rear so they end up


with a system that transceives mainly to the


front.


The exception to the rule would be a flatbed


trailer. I use a 102" whip on my T2000 which is

mounted to a flat bar attached to the frame


that extends past the edge of the trailer which


allows the antenna to "see" behind the trailer.


The antenna is supported roughly 6' above the

mounting point using a custom made


plexiglass bracket.


I have also attached 2 braided steel cables to


frame which drag the road during travel and


supply a make-shift earth


ground when parked.


I will be flat honest with you and say that this


system gets out farther then i care for


sometimes.


It also works well for sky-wave propagation


when conditions permit. My 4x4 truck uses a


pedestal mount 102" whip and a 24" x 24"


sheet of stainless,




Congratulations. The "Richochet Skip Dish" has been used for years on
vehicles around here,,practically standard fare on many pickup trucks
'round here. And you're right, it makes one hell of a difference,,,it
gets up and out,,,,.since you have a 4 X 4, pull that bad boy into some
water, like on the edge of the lake or on a beach. Add a Leece-Neville
or two and you're humming.


_
the pedestal is mounted to the floor of the bed


1.5' behind the cab and cut to length with the


top of the bed, the stainless sheet is


sandwiched between the top of the pedestal


and the bottom of the antenna. Very powerful


system using a highly tuned 25 LTD


Mad-Dog




Nice set up for any eleven meter activity. Attaching the mast and
Richochet dish to a steel toolbox is also another popular method. Copper
strap as a ground is preferred instead of wire because of differing
inductance value.