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Text File
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1992-12-22
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3KB
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84 lines
SUBJECT: Wire antennas- part 7
INVERTED VEE
This antenna is basically a half wave dipole with each leg sloped
down at a 45 degree angle from the horizontal, 180 degrees apart.
X feed point
/ | \
/ | \
/ | \ element leg
/ | \
/ | \
|
- tower or mast
----------X---------- Top view
The overall length of the Inverted Vee is slightly longer than the
standard wire dipole. For 10m, the length is only 2 inches longer.
This antenna can be fed directly with 50 or 75 ohm coax, but it is
suggested that a 1:1 BALUN be used. The tips of the Inverted Vee should
be kept well off the ground as the RF voltage levels are high at the ends.
This is more of a protection for young ones playing around the area.
If you recall the formula c=sqrt(a^2 + b^2) and insert the length of
the element leg for c. Use the fact that a = b because of the 45 degree
angles between the mast and the element leg and the angle between the
element leg and the horizontal, this will equate to:
c = sqrt(2a^2) => a = sqrt(0.5c^2)
This will give you the value of a which is the height of the mast
at the horizontal line to the end of the element leg. Add eight feet
for protection from the high RF voltage levels and you have the height
of the mast required to support your Inverted Vee antenna.
EX: 40m Inverted Vee; 66'2" @ 7.15 MHz
(66'2")/2 = 33'1"
c=33'1" => 33.0833 decimal
a = sqrt(0.5c^2) = 23.39345 => + 8 = 31.39345 => 31'4.75"
Thus the mast height is 31' 4.75" to support a 40m Inverted Vee,
minimum.
The Inverted Vee is basically omni although the pattern is not quite
but close enough. The gain is basically unity over a good ground. It is
an inexpensive antenna to build and performs very well on all HF/MF bands.
---------------------------
BEVERAGE ANTENNA
This is also a basic wire antenna of which is one wave length or
longer. Normal designs are one wave and this must be kept in mind
when placing one on the property. Once installed the direction is
fixed.
The beverage antenna has a low angle of propagation which makes it
excellent for the lower bands (30m, 40m, 75/80m, & 160m).
-------------------------------
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Rx }|{ Zo
__}|{ |
| G & radials
G
The Beverage is inefficient as a transmitting antenna and it is
suggested that it be used as a receiving antenna only. The pattern
of the beverage is similar to a good yagi.
Formulas and specifics for this antenna can be found in the ARRL
antenna handbook.
-WS