The Electrical experimenter

34 THE ELECTRICAL EXPERIMENTER May, 1 917
A "WIRELESS" AUTO RADIATOR
EMBLEM FOR AUTOS.
The base ot this nifty and appropriate
auto emblem is made from an irregular
shaped piece of wood, Ya inch thick and
about 8 inches long, by 3^ inches wide at
the broadest end. The rocky effect is ob-
Ifirestopi/sfiMfonibJf. ®
Something New in a "Wireless" Radiator
Emblem for Radio Enthusiasts Who Own
a Car. By Pushing a Button on the Dash,
Sparks Are Caused to Jump a Small Gap
Inside the Miniature House.
tained by mixing thin glue and plaster of
paris and water to a thick paste and moulding
it on the base, which has several quarter
inch holes bored through it, to give the
plaster a secure foundation. Papier-inache
is very good for the purpose or the base
can very well be moulded from white metal
or lead and afterward painted. The radio
masts and connections will then, of course,
have to be especially well insulated. The
coil and condenser must be kept close to
the spark gap.
One of the masts is 8 inches long and
the other 4 inches long, made of 3/16 inch
brass or steel. The longer one is sunk
into the plaster about two inches and the
shorter one about 1 inch. The spreaders,
V% by 2^2 inches, are equally divided for
the four wires which are of No. 24 bare
copper. The lead in rattail is soldered to
the middle of the aerial. The insulators
are tiny drops of black sealing wax moulded
in ball fashion about the wire.
Ropes of fine fish line and guys of silk
cord are put on, also a station constructed
of cardboard is placed at the base of the
Bafff
lllllllh
^Pi/i/) i>t///on
Buih/ng Spk co//^
r,nr}i^^i%^%^
6/oss^ Corxf
{e[\
Circuits of Miniature Radio System Used as
Radiator Decoration for Autos. Be Sure to
Show Your Credentials to the Village 'Constabile."
or By Heck. He May Take You for
a "Spy," with a Consarned. New-fangled
"Wireless." Yesslree.
taller pole. The whole, except the aerial,
is given two coats of enamel, the poles
being white and the ground and rocks of
THE
A Study of the Law of Response of the
Silicon Detector
special form of silicon detector
receiver designed by E. Merritt for
use with short electric waves, and
reported upon at the meeting of the Physical
Society, Eebruary 27, 1915, showed certain
peculiarities which made desirable a
further study of the device. The investigation
described in the following paper by
Louise S. McDowell and Frances G. Wick
in the Physical Kcviczi.^, includes, first, a
study of the receiving device and the conditions
under which it can be used to best
advantage, and, secondly, a study of the
law of response of the silicon detector with
a variation in the energy of the incident
wave produced by the rotation of a screen
of parallel wires.
The oscillator, receiver and screen were
arranged as shown in diagram. The oscillator
.b' consisted of a small spark gap in
kerosene, extended by two straight aluminum
wires U'll', to a length of 51 cm., and
connected thru water resistances, HH, to
the secondary of a sinall automobile induction
coil. A.', using about 6 volts. The
water resistances introduced served to
damp any oscillations from the coil which
might have produced disturbances.
The receiver consisted of a silicon detector,
D, in series with a paper telephone condenser,
C, of 1 mfd. capacity', and with a
loop of wire, A'R. The connections to this
loop were made by mercury cups, MM. A
sensitive galvanometer, Gal., Leeds & Xorthrup
type H, was shunted around the condenser.
An aluminum rod, OP, acting as
a resonator, was supported parallel and
close to the outer wire of the loop. The
length of the resonator was 44.5 cm., giving
the maximum response to the wavelength
used, about 100 cm.
Between the receiver and the oscillator
and parallel to them was placed a screen,
EF, which could be rotated thru known
angles. It consisted of iron wires stretched
parallel to each other about 3 cm. apart,
upon a wooden frame 2 metres square. An
additional fixt screen of tin and wire netting,
VAB, 3 metres high and 4 metres
broad, completely divided the room, except
for an opening, AB, left in the center. The
rotating screen was placed close to this
opening, on the side toward the receiver,
at distances varying from 5 cm. to 10 cm.
for different sets of observations.
Merritt, in his experiments with the receiving
device, had noted that when the
screen was placed with its wires parallel to
the oscillator, the position which should
allow no transmission, there was still considerable
effect upon the receiver, amount-
green and gray respectively. The copper
wires are lacquered after being polished.
Two heavily insulated wires (secondary
cable) are then run up thru the hood
of the car from a spark coil and condenser,
which are operated from a push button on
the dash or wheel, the same as a horn is
controlled. These wires are connected to
a brass wire spark gap of about 'i inch,
which has been previously moulded into
the plaster and which the station building
conceals. If an ordinary ignition coil is
used, then a suitable condenser may be
formed of about four 4x5 glass plates,
coated on both sides with tinfoil leaves 1
inch smaller all around. Connect as shown
in cut.
The rest is easily imagined. The surprise
at the sight of the tiny flashing windows
and the crash of the spark gap is
bound to command attention from anyone.
Try it boys and see if I'm right.
Contributed bv LES GLEIM.
ing at the least to about one-fifth of the
maximum effect, when the wires were vertical
(the position for complete transmission).
The cause of this residual effect
was unknown. He observed, also, that
as the wire screen was rotated thru 3bO
deg. there was a variation in the response
in the different quadrants. Early in the
present experimental work it was found
that when the resonator OP, Fig. 1, was
removed the receiving apparatus still responded,
although weakly, to waves from
the oscillator. The receiver was then
studied in order to discover what changes
in the design would affect the response
without the resonator, and how it could be
reduced to the minimum consistent with
sensitiveness of the receiver as a whole;
also to discover the cause of the residual
effect when the screen was in the position
of no transmission. Experiments were
made with the plane of the receiver both
vertical and horizontal.
Receiver in the Vertical Plane.
Tlie receiver was mounted on a T-shaped
board and suspended by rubber bands from
a cross-bar rigidly fastened to the ceiling.
To prevent reflections, practically all removable
metal was taken from the room
and^ from the adjoining rooms. To reduce
any difficulties arising from reflections
from surrounding metal objects, the room
was completely divided cross-wise by the
fi.xt screen described above, and the rotating
screen was placed in front of the
Miniature Radio Transmitter and Receptor.
With Screen E-F Interposed Between Them
and By Which Means the Law of Response
of the Silicon Detector Was Studied.
opening. The residual effect was then
found to be considerably reduced.
The screen was then rotated thru
360 deg. and readings were taken every
20 deg. both with and without the resonator.
From the observations made three
curves were plotted, in which the ordinates
were galvanometer deflections and the abscissae
the angles between the parallel
wires of the rotating screen and the ver-
tical.
The curve obtained with the resonator
had a maximum at 15 deg. and a minimum
at UK) deg.. whereas without the resonator
four maxima at the 45 deg. positions were
obtained. Curves taken out of doors were
similar in form to those obtained indoors.
To determine the effect of the design of
the receiver upon the response without the
resonator, series of observations were made
with loops of various shapes and sizes. To
get the effect upon the loop alone, the receiver
was screened by a tin cylinder up
to the mercury cups -l/.l/. To test tlie re-
.sponse to the vertical and horizontal com-
(Contiiiucd on page 74)