New-York tribune., 1922-06-25
Operation OF
Vario-Coupler
Described
Its Difference From Loose.
Coupler Described rs
Well as Functions OF
Both i'm Radio Circuit
Vario-CoupIer Is the Best
Its Coupling Can BE Varied
Without Secondary Nov.
ing Out of Magnetic Field

,ector. have just made a yario-
coupler but d, doesn't work. although
use the same circuit that ! use with
the ioosc-coupler. what Is the
irouble,'
This query is typical OF many that
reach me, and bound up in 1t there Is
a fundamental fact which puzzles many
radio novices. They cannot understand
whv Il is that there is such big dii-
ference between the two instruments
although their functions arc practical
~ the same. In view Of this, ] have
come 10 the conclusion that II would
he a good subject to discuss thorough
ly this week.
In the first place. in order to get
complete understanding oil the two IN
s,ruments. we will consider just what
kind OF duties they perform IN a wire
less circuit. Il is fact that both the
loose-eoupler and the vario-eoupler
pcrform the same work. but they do 1t
in slightly different manner. and It
is because OF this that many OF the
fans are puzzled.
Both Are Oscillating Transformers
Both OF them are transformers. They
act Just in the same manner as any
ether transformer IN an electrical cir
cult. by inducing a current in the sec
ordary when an alternating current
passes through the primary. In this
case. however, they are dealing with
very high frequency alternating cur
rents which arc in an oscillatIng state.
In fact. they we're originally referred
20 AS oscillating transformers. and still
are IN some quarters
The two instruments differ from or
dinary transformers. however. IN that
thcv are made variable so that they
can be- placed into resonance with GER
tain electric currents that are alter
mating M a certain definite frequency,
n characteristic tha, is known as tun-
ing. In addition 90 this. they also are
made variable IN such manner that the
amount Of induction taking place be-
tween the primary and secondary can
be varied. % Characteristic that ~ called
coupling" Thus you speak Of vary
ing the coupling Of the secondary.
Such arc the two characteristics OF
these two instruments. Before de-
f scribing tho method by which they are
achieved IL would be well TO inquire
into the reason why the characteristics
should be necessary. The loosc-eoupler
or yario-coupler are instruments that
enable Us TO construct what Is called
two-circuit receiver. wherein the
frat or urinary circuit consists OF the
aerial. an aerial-tuning condenser, and
,bc ground connection, and the see
ondary circuit consists OF the second
arv winding of the instrument and
variable condenser shunted across Il.
Cuts Down Interference
The objee, Of having double.cir-
cuii receiver is 10 cut down as far as
possiblc all interference caused by
electromagnetic waves that are not Of
Tie same length as the wave Of the
station we desire % listen 90. There
Is no, the slightcs, doubt about the
two.circuit receiver doing quite 10;
/ in this direction. and Y is a very val
liable system in radio work.
consider just what takes place when
~ are tuning In the first place We
adjust the aerial tuning condenser and
the primary OF the particular type OF
! coil go are using. The aerial. OF
course. will pick and pass 10 ground
/ whatever waves pass over II. In theory
none but those in tune with the aerial
circuit would aetuate the dctector As
d Il
waves out Of tune do actuate the de-
I tcctor. and cause interference.
J Now. II We add a secondary circuit
which is also attuncd to the particular
wavc-lcngth -vc desire % receive from.
T u will be readily seen that the possi-
h.litv of the unwrnted signals passing
through both circuits will be greatly
decreased In actuality this is the
/ case. although. Of course. all inter
ference is not always tuned out.
Variable Condenser Necessary
II We look upon the electromagnetic
waves which are surging through the
ether .as though they were burglars,
and then look upon the receiver as
though IL were a safe, which the waves,
like tho burglars. were trying 20 enter.
the value Of tho double-creuit receiver
can be seen. IL is an easy matter
I for n burglar 20 pick a safe that is
equipped with lock consisting OF
single combination. but IL is not so
easy 10 pick a lock having two eombi-
nations. although u can be- done. the
task is harder. So it is with the waves.
This is quite a long introduction 70
explain why a vario-coupler won't work
where a loose coupler would. Well, in
investigating the complaints such as
that quoted in the first paragraph OF
this article. il invariably turns out
that the complainant was not using n
variable condenser across the second
ary OF his loose-coupler, and OF course
+ tried 20 work the vario-coupler in the
same manner.
Secondary Must Be Variable
Now a loose coupler will work per-
I foc.ly well in quite a lot Of cases with
out a condenser across the secondary
E winding. despite the fact that capacity
b is very necessary quality in an os-
cillating circuit. II can be done. how
ever. because Of two things. In the
Z first place. every coil which is wound
with parallel turns has the quality Of
capacity 10 n marked degree. and in
the second place. the secondary OF the
ose-coupler is made variable. In
other words the secondary circuit in
this ease can be made variable and
put into resonance with the incoming
wave.
The var.o-coupler is entirely differ
cnt In this ease the secondary Is not
variable. and therefore condenser is
very necessary across IL in order that
the circuit can be varied and put into
resonance with the desired wave. The
v.iuc ~ the yario-coupler over the