New-York tribune., 1922-04-23
'ublic Phone
Service to
Ships Soon
nepends on Result Of Tests
With Bridge Receiver
Which Eliminates Effect
Of Sending Apparatus
Tests on S. S. America
Permit Telephone and Tele-
graph Operation on One
Aerial simultaneously

Ht a AJ'ih III tdt1COISlS
During last week radio fans In the
Unity of the Atlantic seahoard, and
.-v In middle Western states, had
=. privilege Of listening in to one OF
g most important tests in the dc
,,cpnent OF radio-telephonv, when
i, steamship America on IT'S voyage to
i.,opo conducted a telephone convcr-
/ ntion with persons ashore while the
i C,.les. operator aboard was using
90 same aerial for tho purposes of
rndirg telegraph messages.
Most Of the fans Will remember that
s.ing the first day Of the test recep-
,n from the America was little
csker than in former voyages, and
sey viii also remember hearing the
perimenter OF board say that ne had
q. ret been able to connect UP the set
.,-rectly according to tho diagrams
he test proceeded better later in the
yoysgs.
Ia view Of this conversation It Is my
,uroo.e in this story 70 outline the
manner IN which it is possible to con-
iuc. two-way conversation by wire
eos at the same time shat wireless tele-
raph messages are being sent from the
,sme aerial,
Bridge Set Solves Problem
The apparatus used FOR thia pur-
pose was developed by Ernest T. "
ueYanderson, the noted radio engineer
iuring the war, but has only recently
been applied 10 commercial purposes.
/ II consists of u "bridgo receiver"
| which is based in principle upon the
characteristics OF the wellknown
Theatstono Bridge for obtaining
balances between circuits, In other
word. tho circuit really acts as deli
cate balance with the circuits as the
scales. This is different instru nent
70 the one recently described in these
columns.
Now In order 60 obtain results with
this receiver 1t is necessary to have
swo distinct Tials suspended between
the TWO rasts Of the ship, or one aerial
cut in with insulators SO that one por-
ION can be used for transmitting pur-
poses and the other for receiving mes
ssges, Ar Idea oS the problem that
rad 10 be overcome in making the
b-idge receiver function perfectly can
perhaps be best explained IN the words
of Mr. Alexanderson.
II two sets of wires are mounted
On the same 1nasts," he said, "the radi-
s.on from one set TO the other IS OBJ
yously so strong that the overpower-
.ag Of al ordinary receiving set by the
transmitted energy would be almost
q the same order Of magnitude as II
dentical wires were used.
The Quantitative relations may be
better appreciated by menuoning spe-
ci6c figures In the tests made in
|Schnectady the receiving antenna con.
s;sts Of five wires mounted ae an
umbrella around the mainmast, while
the sending antenna consists Of Two
wires extending from this mast to an
other building. The capacity 30 ground
o. the sending antenna is .U03 micro
,arads. the receiving antenna .0Oll
micro-farads and the mutual capacity
such that 10000 volts on the sending
Mtenna produces 500 volts on the re-
ewing antenna when it is discon-
r.c.ed.
High Voltage on Aerials
awhile il is obvious that an sntenna
willating with 500 volts continuous
wyes could not be used with ordinary
..hods OF reception, tho system OF
Mtralizatiou has proven 80 ettectiVe
lbs. an ordinary receiving set can be
ud for receiving signals from such
dances as the Pacific Coast 1000
rlss) without any appreciable inter
sssnce from continuous wave radla-
gm from the main anntenna Of 20 am
pres and 10000 volts"
Iro methods Of naturalization were
tied before the successful brldge re-
ai7.r was developd. The FIRST con-
listed OF system OF inductlve neu~
/ imitation. but this was discarded tor
az tpy nf ~.
| tire neutraliZation-
The latter consists Of system OF
,ndensers. known as the counterpolse
Et exposure condensers. The counter
wise IS connected in series to the Se-
ewing aerial, and the exposure con-
tsnsers are joined up IN series pc"
tween the sending and receiving aeriais'
Regarding the tests made, with thIs
t,ilge receiver, Mr. Ale xanderson said !:
The qeutralization by this method
Il SO sharp that the influence of the
two snntennae on each other is reduceo q
muth below other sources OF disturb
sace. The principal remaining disturb"
sace. caused by the transmitting sys-
ten are the magnetic strays within the
building. IN 20 far as these strays
are il phase with the antenna radla-
ton, they are automatically taken care
Il VIZ III 0FNtF2IlGlnS ING "ufS'l'oS'
All Interference Eliminated
The local etrays can be effectively
nsu,ralized by i1tercepting the stfaye
on moderate sized wire loop IN the
Aeehborhood of the receiving set ano
'mpressing the potential so generated
on little coil mounted with an ad'
lustablc counting close to the secon'
Gary loading coil of the receiving set.
In connection, with the America tests
/ Y. Amy, the short wave antenna ex
pm, Dho is an engineer OF the kadlo
Octloration, said: j.,
The original installation on thet
Ansrica was made only 70 test ou'
.noer actual service conditions the
'fohlem Of two way telephone oper-
aNon. TIE ether for the first time
pscama merely an intermediate to'
lie in the connection between pas
"'gcr and land subscriber. These
t'ts were very successful, but 1t was
'1nd that operation was somewha'
lnltsd by the right OF way Whlcf
id to be observed for the regular
adio telegraph set on the vesse
1t is thi. limitation which the en-
.aeers have sought TO eliminate TINS
H!age. The circuits for attaining sim
,~sneous operation Of the telephone
80 the telegraph, which have beer
"ked out, and the tests Of the SHY
service tests to make sure that al
stfts Of the system viii work together
ah 100 per cent Of certainty under
.Scondltions. It is expected that after
Inc details have been finally worked
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