Evening star., 1924-03-18
HEIGHT ESSENTIAL
ANTENNA element
Tern Refers to Distance From
Ground Connection to Center
Of Exposed Area.
EFFECT ON INTERFERENCE
Must Endeavor to Select Appro-
pirate Location.

The element Of the antenna which
determines it's ability to pick up or
give on signals is its effective height.
The term "effective height" does not
mean the height from the ground
connection to its topmost point, but
1t more nearly the average height
from ground connection to the center Of
its exposed area For an antenna con-
sisting only Of straight vertical
wire the effective height is about
two-thirds its actual height, while
for an antenna having a large hori-
zontal top structure the effective
height Is very nearly the actual
height The only purpose of the hori-
zontal top element of a receiving
antenna is to give a greater effective
height for given actual height
When regenerative vacuum tube
receiver is used, the extent to which
the signal can be built UP by regen-
Grafton is Independent of the antenna
height Ii all parts OF the antenna are
equally exposed to the incoming sig
naI. However, the amount Of inter
proportionate to the height, and we
must therefore endeavor to select a
location which will permit of mini
mum height.
ComproAise Needed.
As the lower part Of the antenna
VIII usually be more, or less shielded,
1t is necessary to make some compro
mise between signal strength and Sc
lectivity. For installation in cities, q
height OF twenty feet with a hori-
zontai top of the same length will
usually be found ample for reception
of distant signals. For use when in
terference is slight, or in country
districts, the height may be increased
to thirty feet. 1t Is, Of course, as
sumed that for strictly local recep-
1t is unnecessary to use more than
one wire for any part of the antenna,
and the size Of this wire is unimpor
tant. 1t should be well insulated at
far as possible from conducting OBJ
jects. If the outer end of the top wire
Is attached to a tree, a break insu-
lator is placed in the wire well out
side the branches. This top wire
jects such as a metal roof, as the
effective height of the antenna will
probably be about the height of this
top wire above the metal roof. If a
supporting structure is available. a
horizontal part will be satisfactory,
or it may extend in a diagonal direc-
ton from the side of the building
near the receiving set to point some
twenty or thirty feet above on an
adjoining building or other support,
with clear space between
For the best results the ground
connection should be made to some
conducting area on about the same
level as the receiver. A steam or hot
water heating system gives a good
ground Avoid long ground wire,
as this gives height and lack of selec-
tivity without compensating addi-
tional signal strength. This is an i'm
portant point when the receiver is
installed in an upper floor of a build
ing such as an apartment In this
latter case the piping system of the
building will furnish a good ground
Never run q separate wire down to
the ground floor. The wires from an
tenna and ground where they ap-
proach the receiver should be sepa-
rated as much as possible, and the
receiver should be placed as near as
possible to the point where the an
ground connection should be made to
the nearest part of the conducting
system which is to form the ground,
and it is often an advantage to con-
meet to more than one conductor
such as the heating and water or gas
pipes.
If your receiving set is not giving
the results you think it should, look
over your antenna structure to see
Thus it is possible that by change
in the height you can obtain the Sc
lectivity desired, or by a change in
it's location you can improve the
strength of signals from distant sta
tionS.