The Challis messenger. (Challis, Idaho) 1912-current, 1925-07-01

components are all standard, and the
number and arrangement of the vard-
Gus stages are given just as a sugges-
ton to the experimenter.
| As matter of fact, the writer
strongly recommends the reader TO
commence experiments with only three
stages Of K. F., as the selectivity will
be found to be SO great, In a well-laid-
out receiver using good low-loss COM
ponents. that two condensers will be
found to be quite enough to handle.
1t matters little whether the ticker
coil Is coupled to the aperiodic aerial
coll or to the wave trap inductance.
Those who prefer to use plug-in coils
can use an ordinary .three-con holder
In this position.
Similarly, plug-in coils. mounted in
side the cabinet, may be used for the
interstage K. F. chokes, which are
shown variable In the diagram This
variability is desirable because, In a
sense. a choke coil of this sort Is not
absolutely aperioidic. A coil which
will present sufficient impedance to
certain frequency to cause the neces-
sary build-up of oscillation amplitude,
will present a negligible impedance to
another much lower frequency.
Thus, If plug-in coils are used, they
can be changed to suit the wave length
being received. Nos. $50, 200 or $50
will cover the American broadcast
band satisfactorily.
Alternative Choke Coil.
An alternative choke coil which can
be made up by those who desire maxi
mum possible efficiency on any given
wave length consists Of $50 turns of
No. 40 g. g. c. resistance wire wound
on a former about 2% inches In diam
eter. Tappings are taken to ten
point rotary switch from the ends OF
the coil, and from the f1ftieth turn
From the iftieth turn TO the one hun
dred and twentieth tappings are made
at every tenth turn
The switch for this coil may be
mounted on the face Of the panel. OF,
more conveniently, on the end Of the
coll, which can be mounted on the
Dashboard This is a point for the
experimenter himself to settle.
The interstage R. F. wave trap coils
may be wound as cylindrical coils. and
the few turns Of the aperiodic plate
coils wound over the central part of
the winding. In this way turns can
easily be put on or taken off during
the course Of experiments. The aerial
coils can be made up in the same man.
ner II plug-in coils are not used
There is, Of course, no reason why
special low-loss coils Of the various
basket-wound types should not be
made up, the few turns of the aperi-
odic coils being wound on the same
former to insure tight coupling.
Having familiarized himself with the
method of tuning. the experimenter
may proceed to add as many stages OF
R. F. as he pleases, but if more than
three are employed it Is practically
that multiple condenser be
used in conjunction with carefully
matched coils.
Suggestions Of Layout.
The main thing to bear in mind
when arranging the layout is to avoid
in the R. F. circuits and
to so arrange all coils that no interac-
ton can occur between them
Using only three stages Of R. F. and
40 A F., many Britishers report loud
speaker signals from American sta
ions almost every night. with an un-
usual absence OF fading and freedom
from distortion. This alone speaks |
rolumes for the efficiency of the re-
,eiver for, although many different |
-ypes of receivers in use in England /
.oday will bring in American stations !
regularly. fading, swinging and might |
effect" distortion are almost always /
present.
AS regards selectivity. 1t has been /
'ound possible. within a mile or so of |
he local station, TO completely tune
I out and receive uninterruptedly
lpon a wave length within a few