Evening star., 1924-05-31
How to Build a Supersensitive In
door Aerial Receiyer-Part III.

Nos. II, IL and 13 are radio fire.
quency vario transformers, according
to diagrams published previously with
this series
A good type of fixed transformer
can be used. but much better results
will be obtained If vario transform
ers are used.
Nos. IA and Is are standard audio
frequency transformers.
No. IA may be a high ratio trans
former. Best results In quality, how
ever. will be obtained II low ratio
transformers are used in both stages.
Since there is plenty of amplification
before the detector, giving good
signal In the detector stage, 1t is not
necessary to have high amplification
in the audio frequency stages.
No. II is the negative A battery
post: No. Is is the positive A battery
post.
Nos. 10 and 20 are double-circuit
jacks. In these jacks A and d are the
outside springs and and c the in
side springs.
The inside springs marked B make
contact with the A springs. and the
inside springs marked c make con-
tact with the D springs.
No. 21 is single-circuit jack.
No. % Is the coil used for tuning.
This consists of sixty turns of No. %
D. s. c. wire wound on a tube 3
inches in diameter and 21s inches
long. The coil is tapped at every
ten turns.
No 2s is the negative A battery ter
Nos. "a, 81, IS. 80. 80 and ss are the
vacuum tube jackets, the type de-
pending on the tubes used in the cir
cult.
No. 25 is a mid. fixed condenser.
No. 26 is the positive B battery ter
fn ha nj
Grid Leak and Condenser.
No 20 is combination grid leak and
condenser. The condenser should
have a value of .0o025 MID, while the
grid leak should have a resistance of
from to megohms, depending on
the characteristics of the tube used
as a detector. Best results VIII De
obtained by substituting different
values until the correct one is found
No. 81 is tbe positive B battery ter
miral for the detector stage.
No. "a Is the Az volt c battery.
Number 35 is the positive battery
terminal for the audio amplificat1on
Wiring the receiver is not as COM
plicated as 1t may seem. If the di-
rections given below are followed
carefully no trouble will be expe-
rienced in making all the connections
properly.
Begin Dy INC
10, 20, 80, 40, so and 60 switch points
of switch with the corresponding
switch points of switch 6. The NUM-
ber switch points of the switches
are not connected together.
Connection Of Taps.
Next place the coil back of the
switch points and begin connecting
the taps of the coil with the switch
points. The tap at the tenth turn is
connected with the wire which connects
the number 10 switch points of both
switches; that at the twentieth turn
is connected with the wire which
joins the number 30 switch points, and
SO on down the line till the last tap
at the sixtieth turn has been con-
nected with the wire which joins the
number 60 switch points of both
switches.
The number switch points of
switch is left unconnected. 1t
merely serves as a blind" contact
when it is desired to disconnect the
switch arm of switch from coil %.
The aerial post 1 is connected with
the switch arm Of switch 4. Next
connect, in the order named, the G
terminal of socket "a, the begin
ming or top end of winding %,
the B terminal of switch 3 and the A