The sun., 1919-04-03
YANKEES BLOCKED
WIRELESS BARRAGE
Germany Had Drowned Radio
Of Allies When America
Entered the War.
NAVY MADE NEW EARS
E. F. w. AlexandersOn Also
Tells Of Great Progress Made
in Aerial Telephone.

Powerful German wireless installations
the Allies as part of deliberate policy.
How our navy, on entering the war.
overcame this interference, and in doing
SO made n remarkable stride In the
whole science of radio communication.
was described last night by one of the
men who led in the achievement He
is r. F. w. Alexanderson, consulting
engineer of the General Electric Com
pany. and he described the device before
the Radio Institute In the United En-
cheering Societies Building in 20 West
rhirty-ninth street.
His invention Is the "barrage receiver
1t permits an operator to turn n deaf
ear, electrically as well as literally. TO
all messages which may come through
the ether except that particular message
which he desires to hear. The invention
was kept secret until the end of the war
ut the request of the army and navy. 1t
has been demonstrated successfully and
Is now in navy use.
THE object of this development" said
Mr.. Alexanderson, was to provide means
for neutralizing the overwhelming inten-
sity of the transmitted signal 80 as to
make the receiving set sensitive to the
faint impulses of the distant signal.
Popularity speaking. the correspondent
equivalent in sound waves would be to
have an ear which could be SO adjusted
that n person could stand close TO n
steam whistle without hearing the whis-
tie. but at the same time listen to n
person speaking from n distance OF a
few hundred feet. A successful solution
OF this problem was found.
Also Adopted by French.
During the war the problem presented
Itself Distances are only relative and
q steam whistle located in Germany
night mako such nvise that 1t would
completely drown out both in England
and France the sound of the voice call
ing from America. To find a way TO
coupteract such a contingency, was seri-
ously considered by the Inter-Alied
wss adopted by the American as well as
by the French Government after the
first demonstration. has become known
as the "barrage receiver" This may
be used not only in time of war to
counteract the offensive barrage of an
enemy radio station. but it may be
used to multiply the number of peaceful
communications that may be carried on
simultaneously without disturbing each
other.
Mr.. Alexander. described also another
invention of even more Importance in
wireless telephony. an instrument which
automaticallyNchange equipment to per-
NIT both sending and receiving. just
as Is accomplished in ordinary telephon-
ing.
Everybody who has experimental with
radio telephony undoubtedly has OBJ
served" said Mr.. Alexanderson. that the
interchange of ideas is not satisfactory II
II is necessary to manipulate a switch
of some kind In order to change the
equipment from sending to receiving.
Even II an automatic device is used for
performing the change over, two per-
sons are apt to say hello simultane-
ously, then wait for an answer stimuli
taneously, then say hello again, and
finally give it up in despair.
at therefore can be said that one OF
the most important problems from the
point of view of making radio telephony
practical and useful for the genera
public is to devise a simple method OF
duplex operation whereby the speaker
is able to hear the voice of the other
person in the same way as is done or
the wire lines.
Connected with the exchanges.
I'm the work that has been done t.
attain this several possibilities hav,
presented themselves. One was accom-
plished by system of naturalization
in the receiving circuit whereby high
degree of selectivity was attained be
tween the sending and receiving wave
lengths. Each pair of sending and re
ceiving stations were interconnected b.
a wire line. and Furthermore. were com
nected to the exchange of the local tele
phone system, so that any subscriber oil
the telephone system could be connecte,
with the radio system. With this ar
rangement the RADIO system has the sam
relation to the subscriber as a toll line
The radio operator takes the place OF tn
toll operator, and to the subscriber tn
method of communication is the sam
as a conversation over the toll line"
Other methods described by Mr.. Alex
anderson in highly technical phra seoiog
indicated the rapid advance that is bein
made in radio telephony In the matter o
transmitting the human voice over vas
distances and in sending and receiving
oral messages clearly and distinctly
His address was heard by about 40
members of the Radio Institute, whic