7
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
L A B E L I T A L Y S R L
- V i a S . A l l e n d e , 5 9 – 4 1 1 2 2 M O D E N A
T E L : 0 5 9 / 3 6 2 9 9 3 F A X : 0 5 9 / 3 7 6 0 5 6
P . I V A 0 2 5 7 8 7 5 0 3 6 2 C a p i t a l e S o c i a l e 3 2 . 5 0 0 E u r o
w e b - w w w . l a b e l i t a l y . c o m e - m a i l - i n f o @ l a b e l i t a l y . c o m
BEAM TILT
is used in radio to aim the main lobe of the vertical plane radiation pattern of an antenna below (or
above) the horizontal plane. The simplest way is mechanical beam tilt where the antenna is
physically mounted in such a manner as to lower the angle of the signal on one side. However this
also raises it on the other side making it useful in only very limited situations.
Horizontal and vertical radiation
patterns,
the
latter
with
a
pronounced downward beam tilt
More common is electrical beam
tilt, where the phasing between
antenna elements is tweaked to
make the signal go down (usually)
in all directions. This is extremely
useful when the antenna is at a
very high point and the edge of
the signal is likely to miss the
target entirely.
Electrical tilting, front and back lobes tilt in same direction : for example an electrical downtilt will
make both front lobe and back lobe tilt down. This is the property used in the above example
where the signal is pointed down in all directions. On the contrary the mechanical downtilting will
make the front lobe tilt down and the back lobe tilt up. In almost all practical cases antennas are
only tilted down . Occasionally the mechanical and electrical tilt will be used together for odd
situations in order to create greater beam tilt in one direction than the other, mainly to
accommodate unusual terrain. Along with “null fill” beam tilt is the essential parameter controlling
the focus of radio communications and together they can create almost infinite combinations of 3-D
radiation patterns for any situation.
NULL FILL
is used in radio antenna systems which are located on mountains or tall towers to prevent too
much of the signal from overshooting the nearest part of intended coverage area. Phasing is used
between antenna elements to take power away from the main lobe and electrically direct more of it
at a more downward angle in the vertical plane. This requires a phased array. Changing the
relative power supplied to each element also changes the radiation pattern. Often both methods
are used in combination.
SUGGESTED GUYED MAST SECTION
Is suggested install FM Dipole Antennas over guyed masts because the section higher than
110mm can be increase the SWR value and modify the radiation pattern.
DISTANCE ESTIMATION BETWEEN FM ANTENNA BAYS
Wave Lenght =
λ
= 300 : f(MHz)
Distance between antenna bays ( all antenna types) = d
d (suggested) =
λ
x 0.85
EXAMPLES
88MHz
➾
λ
= 300 : 88 = 3.41 mt
➾
d = 3.41 x 0.85 = 2.9 mt
98MHz
➾
λ
= 300 : 98 = 3.06 mt
➾
d = 3.06 x 0.85 = 2.6 mt
108MHz
➾
λ
= 300 : 108 = 2.78 mt
➾
d = 2.78 x 0.85 = 2.36 mt
Distance d suggested for mid band 2.6mt
