The Washington herald., 1922-03-06

passing through binding post 4,
the other end of which rests gently
by its own weight on the crystal l.
The bare copper wire which was
wrapped tightly around the three
brass woodscrews holding the
crystal in place is lead to and
fastened at the rest of the right
nand switch arm bolt, ", thence
to the upper left-hand binding post
marked "antenna" As much as
possible of this wiring is shown in
Fig. 3.
Directions for Operating.
After all the parts of this
crystal-detector radio receiving set
have been assembled the first es-
sential operation is to adjust the
little piece of wire which rests lightly
on the crystal to a sensitive point.
This may be accomplished in several
different ways: the use of a minia-
ture buzZer transmitter is very
satisfactory. Assuming that the
most sensitive point on the crystal
has, been found by method de-
scribed in paragraph below. "The
Test Buzzer," the rest of the oper-
alton Is to get the radio receiving
set in resonance or in tune with
the station from which one wishes
to hear messages. The tuning of
the receiving set is attained by
adjusting the inductance of the
tuner. That is. one or both of the
switch arms are rotated until the
proper number of turns of wire of
the tuner are made a part of the
metallic circuit between the an
tenna and ground so that together
~ If ha ornNA
the receiving circuit Is in reson-
ance with the particular trans
mitting station. 1t will be remem-
bered that there are ten turns of
wire between each of the first
eight switch contacts and only one
turn of wire between each two of
the other contacts. The tuning of
the receiving set is best accom-
plished by setting the right-hand
switch arm on contact l and ro-
tating the left-hand switch arm
over all its contacts. If the de-
sired signals are not. heard move
the right-hand switch arm to con-
tact and again rotate the left
hand switch arm throughout its
range. Proceed in this manner
until the desired signals are heard
1t will be advantageous for the
one using radio receiving equip
ment to find out the wave frequen-
cies, wave length, used by the sew
eral radio transmitting stations in
his immediate vicinity.
As mentioned previously. II is
easy to find the more sensitive
spots on the crystal by using a test
buZzer. The test buzzer Is used as
miniature local transmitting set
When connected to the receiving
set as shown at z, Figure 3, the
current produced by the buzzer will
be converted into sound by the tele-
phone receivers and the crystal. the
loudness of the sound depending on
what part of the crystal is In con-
tact with the fine wire. To find the
most sensitive spot connect the test
buzzer to the receiving set as di-
rected. close the switch, S. Figure
8, and IL necessary adjust the buzz
zer armature so that a clear note
Is emitted by the buzzer, set the
right-hand switch arm on contact
point No. s, fasten the telephone re-
ceiyers to the binding posts marked
phones" loose the set screw of the
binding post slightly and change
the position of the fine wire, 6,
Figure 3, to several positions of
contact with the crystal until the
loudest sound Is heard in the
phones, then tighten the binding
post set screw. Z, slightly.