The Washington herald. [volume] (Washington, D.C.) 1906-1939, 1922-04-02
TRACESRADI0
DEVELOPMENT
James w. Cook Addresses
Club on New Form of
application.
OLD DEVICES CRUDE
Describes Working of Vacuum
Tubes and Use of Radio
Frequency.
OLD DEVICES CRUDE

At a meeting OF the Washington
Radio Club at 1917 New, York ave-
nue. last evening, James w. Cook, In
an address on Radio Frequency
application" traced the growth
of radio receiving from the day
when the coherer was used as the
first radio detector, to the day of
the crystal -detector and up to the
present moment when the vacuum
tube is the last word in the recep-
ton of radio signals.
Some years ago a radio receiv-
Ing set consisted of a coherer. 4
delicate relay and "A large aerial
wire said Mr. Cook. This crude
device could not be depended on for
continuous service: il could not be
adjusted for varying wave lengths.
and was by no means sensitive.
Then came the crystal detector, re-
quiring no mechanical accessories.
a device much more sensitive than
the coherer. The strength of the
signal depended on the current flow
through crystal and circuit.
Limited to short Distances.
The disadvantages of this devel-
opment in radio science were the
comparatively short distances SsiE-
nails could be received in consider
alton Of the power used at the
transmitting station: easily lost ad-
iustment. which was regained with
difficulty
Mr.. De Forrest invented the
audion tube. The principle had
been stated by Edison that a
hlament heated to incandescencc
gives off negative electrons. De
Forrest applied this principle to
the reception of radio signals.
a filament. wire spiral or grid
and a metallic plate were in
closed in a high vacuum tube. . The
theory was that the lighted fila.
ment gives of negative electrons
which ny off into space at tire
mendous speed.
Plate Given Potential.
IF the grid. between the flament
and the plate has no electric 20
tential. these eIectrOns pass
through the grid and strike tn.
plate. II the plate is g3 zen a b.
tential. say by connecting il with
q 5O-volt dry cell: and the positive
side of the filament to the negative
y
side of this battery. We would then
have a complete circuit The mega
tive electrOns leaving the fiIament
lombard the plate. reducing its Dosi-
tive potential. The plate being cor
nected TO the positive terminal o.
the battery. the. battery will tend
TO maintain the plate at plus poten-
tIal. causing current to flow in
the plate to filamcnt circuit
Mr.. Cook described in detail the
behavior of the vacuum tube under
various changes of hOok-ups which
eventually resulted in the use of the
vacuum tube as a detector of radio
signals. Incoming waves striking
the antenna. which is connected t.
the grid, would induce alternately
positive and negative charges OF
electricity of extremely high fire.
quency depending on the wave
length received. On short waves
this frequency or oscillation is at
least 1000 kilocycles per second.
Able to Detect Signals.
The minute charges Of electrons,"
continued Mr.: Cook, will produce
similar results as obtained with
a battery as source of DO
tential. II we insert sensitive teIe-
phone receivers in series with the
plate circuit we will be able to de-
tect signals when the operator
starts and stops transmitting, or the
dot and dash code. The modern
tube dcteCtOr then is an ampIifieT
which by a slight change of poten-
tial Will control q potential and
current flow of much greater pro-
portions. Because of the delicate ad-
Justment made possible in the modern
receiFing set. said the speaker.
red-sprinE aerial has been operated
with success. Two tubes are used
as detectors. and third as an audo
frequency amplifier to increase tn.
strength of signals. Skillful op-
Grafton is required. however. Z sur.h
an aerial is used We can increase
the strength of signals by inserting a
transformer made OF two coils OF
wire wound on an iron core"
View AmpIifer Invented.
when a signal is so weak that
it is not audible in the phones. or
the potential OF the grid is too low.
we may still make the signals audi
BILE by simplifying them before they
teCtOT tube. This came about by
the Invention of the radio fire.
quency' amplifer. The resistance
coupled amplifier was one Of
the first used, which had lin
tied range Of usefulness. Final
ly. there developed the tuned radio
frequency amplifier which proved
impraCticable for commercial use
because its range was limited. II
required sharp tuning and Unequal
tiles Of tubes had detuning effect
The Invention then of the trans
former coupled radio frequency am
piifier b. Brent Daniel. formerly OF
the ETr"'" of sta ndards, provided
an amplifier which has fixed
coupling. requiring no adjustment.
The range is increased by in
sorting transformers. Advantages
are simpl icity Of operation,
large application which make the
use Of loop aerial practicable.
This type of aerial is today used
extensively and has the advantages
of simplicity and dfrectional effect;