Evening star., 1923-05-27
Cau Reduce Interference

Cp to a few years ago radio COM
munication was for the most part
carried on from transmitting station
to one receiving station; this Is point
to-point communications: fhere were
only few special kinds OF
services, such as time and weather
signals in which messages trans
mitted by radiotelegraph from one
station were received by consider
able number of receiving stations
However signals were transmitted
from a transmitting station in every
direction, and could, If desired. be
received by any receiving station
located within certain distance, re-
eardless Of its direction. A compara-
lively small number of wave lengths
was sufficient to take care of traffic
requirements Practically all radio
communication in the past has been
carried on on wave lengths above
200 meters. according to F. w. Dun
more and +. H. Engel. radio experts
of the bureau of standards.
With the development of radiotele-
phone transmitting apparatus, the
transmission of the voice or music
broadcast by radio has assumed an
important place in the radio field.
Radio waves which are transmitting
the voice or music occupy wider
band of wave lengths than a sharp"
wave transmitting radiotelegraph
signals. Because of this great in
crease in kind of service which
requires u wide band of wave lengths,
there is already considerable inter
ference among broadcasting stations
and between broadcastinG stations
and radiotelegraph stations.
These authorities state that for
point-to-p point communication there
are two important ways OF reducing
such Interference; that is, to direct
the waves radiated from the trans
mitting stations in a narrow beam
toward the receiving station, and to
use short wave lengths, which are
not at present employed.
Some English investigators have
recently reported on the results of
their Investigations on directive
short-wave transmission.
Experiments have recently been
conducted at the bureau Of stand
ards on transmitting apparatus en-
ploying electron tubes, which trans
mits a directed beam of radio waves
and employs waves as short as ten
meters. This system, therefore. offers
substantial relief from Interference
difficulties. It also has possible mill
tary applications. The apparatus has
been used for communication by both
autobiography and radiotlephony.
In the experiments at the bureau OF
standards a reflector has been used
consisting Of short parallel vertical
wires arranged on a frame shaped
like a parabola. This reflector acts
mUcn as an ordinary IlllTToT "OuIu lot
light waves. The radio waves are. in
fact. the same kind of waves as light
waves, but of considerably longer
length. Forty vertical wires were
used and the generating set, with it's
small antenna, was placed at the
focus of the parabola. Each wire was
tuned separately to ten meters by ad-
justing it's length. 1t was found that
about 70 per cent of the radiated
energy could be confined within an
angle Of about rs degrees.
This apparatus is described in
scientific paper No. 469 of the bureau
Of standards, entitled directive Radio
Transmission on a Wave Length of
Ten Meters" by F. w. Dunmore and
F. Fl. Engel. Copies may be obtained
from the superintendent OF docu-
ments,. government printing office,
Washington, d. c. The price is 10
cents