The Washington herald., 1922-03-06
BUREAU EXPERTS
EXPLAIN WORKING
OF RECEIVING SETS
Tuner Can Be Made at
Home-Detector Must
Be Bought.
Continued from Yesterday,

chased.
The tuner. r. shown in Fig. .,
Is a piece Of cardboard or other
non metallic tubing with turns Of
copper wire wound around II. The
cardboard tubing may be an oat-
meal box. Its construction Is
described N detail below.
The crysA detector. s, in Fig. .
may be of very simple design and
quite satisfactory. The crystal. as
It is ordinarily purchased, may be
unmounted or mounted in a little
block Of metal For mechanical
reasons the mounted type may be
more satisfactory. but that Is of no
great, consequence. 1t Is very i'm
portant, however, that very good
tested crystal be used. 1t is prob
able also that a galena crystal VIII
be more satisfactory to the begin
ner. The crystal detector may be
made up Of a tested crystal. three
wood screws, short piece OF copper
wire, a nail. set-screw type Of bind
ing post, and a wood knob or cork.
The tested crystal Is held In posi-
ton on the wood base by three
brass wood-screws as shown at in
Fig. Q. A bare copper wire may be
wrapped tightly around the three
brass screws for contact. The as
sembling of the rest of the crystal
detector is clearly shown in Fig. ..
Pair of Phone Receivers.
For the phone, T, IN Fig. ., 1t Is
desirable to use a pair Of telephone
receivers connected by a headband,
usually called a double telephone
headset. The telephone receivers
may be any of the standard COM
mercial makes having a resistance
of between 1000 and 5000 chms.
The double telephone receivers viii
cost more than all <he other parts
Of the station combined. but II is
desirable to get them. especially II
one plans TO improve his receiving
set later. II one does not cart to
invest in a set of double telephone
receivers a single telephone re-
ceiver with a headband may be
used, although il gives results
somewhat less satisfactory.
The binding posts, switch arms
and switch contacts may all he
purchased from dealers who handle
such goods.
Details OF Construction.
See the tuner. Il, Fig. ,. HaN-
ing supplied oneself with
DleCS vi
inches in diameter and about
n pound of No. %, or No. 26.
double cotton covered copper wire.
one is ready to start the winding OF
tn. tuner. Punch two holes in the
tube about II inch from one end as
shown at on Fig. 3. Weave the
wire through these holes in such a
way that the end of the wire will
be quite firmly anchored, leaving
about IL inches of the wire free for
connections. Start with the remain
der of the wire to wrap the several
turns in. a single layer about the
tube, tightly and closely together.
After 10 complete turns have been
wound on the tube hold those turns
snugly while a tap Is being taken
of. This tap is made by making
a 8 inch loop OF the wire and twist
ing it together at such a place that
IL win be slightly staggered from the
first tap. This method of taking of
taps Is shown quite clearly at U.
| Fig. 3. Proceed in this manner until
twisted taps have been taken OF
| at every 10 turns. After these first
| 70 turns have been wound on the
tube then take of a inch twisted
tap for every succeeding single turn
until 10 additional turns have been
wound on the tube. After winding
the last turn of wire anchor the end
by weaving it through two holes
punched in the tube much as was
done at the start,~1eaving about 12
inches of wire free for connecting.
1t Is to be understood that each of
the IS taps is slightly staggered
from the one just above, SO that the
several taps will not be punched
along one line on the cardboard tube
See Fig. Q. 1t would be advisable,
after winding the tuner as just de-
scribed. to dip the tuner in hot
paraffin. This will help to exclude
moisture.
Panel and Base.
Having completed the tuner to this
point. set 1t aside and construct the
upright panel shown in Fig. 2. This
panel may be a piece of wood ap-
proximately II inch thick. The posi-
tion of the several holes for the
binding post, switch arms and switch
contacts may first be laid out and
drilled. The "antenna" and ground
binding posts may be ordinary Il
inch brass bolts OF sufficient length
and supplied with three nuts and two
washers. The first nut binds the
bolt to the panel. the second nut holds
one OF the short pieces Of stiff wire.
while the third nut holds the antenna
or ground wire as the case may be.
The switch arm with knob shown at
V, Fig. 3, may be purchased In. the
assembled form or 1t may be con-
structed from a thin slice cut from
broomhandle and a bolt of suficient
length equipped with four nuts and
two washers together with a narrow
strip of thin brass somewhat as
shown. The switch contacts, w, Fig.
3, may be Of the, regular type fur
nished for this purpose or they may
be brass bolts equipped with one nut
and one washer each. The switch
contacts should be Just close
enough that the switch arm will
not drop between the contacts but
also far enough apart that the
switch arm can be set so as to
touch only one contact at a time.
The telephone binding post
should preferably be of the set
screw type as shown at X, Fig. g.
Instructions for Wiring.
Having assembled the several
parts Just mentioned and mounted
them on the wood base one is
ready\to connect the several taps
to the switch contacts and attach
the other necessary wires. Scrape
the cotton insulation from the
loop ends of the sixteen twisted
taps as well as from the ends of
the two single wire taps coming
from the first and last turns.
Fasten the bare ends of these