The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1925-06-26

/ tuned by a low-loss condenser CT zoos
mfd capacity.
Ii which is tightly coupled to ID may
consist of a coil Of % turns or less.
! AS low number as eight turns has
been used with success, the deternin-
ing factor being the degree Of tolume
required as against the degree of Sc
iectivity necessary. Eight turns will
give very much greater seIectiyity
than % turns. and the loss of volume
will only be slight. The point is one
which the individual experimenter can
with advantage decide for himself.
Except for the aperiOdic coils the
cOmponents are all standard, and the
number and arrangement of the vari-
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 r. F., as the selectivity will
De found to be so great, in a well-Iaid-
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
coil or to the wave trap inductance.
Those who prefer to use plug-in coils
can use an ordinary three-coil holder
in this position.
Similarly, plug-in coils, mounted in
side the cabinet, may be used for the
| ahnly i.h
shown variable in the diagram. This
variability is desirable because in a
sense, 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. 80, 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 S. s. C. resistance wire wound
on a former about "a inches in diam
eter. Tappings are taken TO ten
point rotary switch from the ends Of
the coil, and from the fiftieth turn.
From the fiftieth turn to the one hum
dred and twentieth tappings are made
at every tenth turn.
The switch for this coil may he
mounted on the face Of the panel. or,
more conveniently, on the end of the
coil, 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 aeriai
coils can be made up in the same man
ner if 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 apert-
| odic coils being wound on the same
former to insure tight coupling.
Having familiarized himself with the
method of tuning, the experimental
may proceed to add as many stages Of
! r. f. as he pleases, but if more than
three are employed it is practically
essential that multiple condenser he
used in conjunction with carefully
matched coils.
Suggestions Of Layout.
The main thing to bear in mind
when arranging the layout is to avoid
overcrowding 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
no A. F., many Britishers report loud
speaker signals from American sta
tons almost every night, with an I'M
usual absence of fading and freedom
| from distortion. This alone speaks
volumes for the efficiency of the re-
ceiver, for. although many different
| types of receivers in use In England
| today will bring in American stations
regularly. fading, swinging and might
effect" distortion are always present.
J AS regards selectivity, it has been
| found possible, within a mile or so of
the local station, to completely tune
| ii out and receive uninterruptedly
upon a wave length within a few
meters of Ii.