The Challis messenger. (Challis, Idaho) 1912-current, 1924-06-04
BY WILLIAM j. SCHNELL

After months of experimental work
we have found that what has been rec
ognized as the standard type of variO-
coupler Is lacking in the one element
most essential to its SUGGESTIVE
circuit to the input Of the radio re-
ceiving set with a minimum Of loss. An
entirely new design, embodied In a
fixed COUPLER known as a selecto-
former has now been devised which
overcomes this serious deficiency in
the old variocoupler. Other defects
which have a serious bearing on re-
ceiver efficiency are also eliminated
by the selectoformer.
Couplers.
Couplers generally are designed so
that the primary unit Is of such an
electrical constant that together with
the antenna constant, with which it
is employed, the desired frequency
band is covered. The primary unit Is
usually tapped so variation in the
value Of the primary circuit can be
had to permit Of obtaining resonance
for any particular incident frequency.
Theoretically 1t was considered that
such coupling resulted in the maxi
mum of received energy in the antenna
system. The secondary circuit was
likewise tuned for the same purpose.
1t was also generally believed that a I
maximum Of energy could be trans
ferred between these two circuits with |
minimum Of loss under the condi-
lions.
Fundamentally, this should be con-
sidered as the basis Of the laws of
action. These conditions
do exist at audio frequencies, but 1t
Is quite different when this trans
former action Is observed at radio fire.
quencies. This applies particularly to
the coupling Of the antenna to the
lnput circuit Of radio frequency am
plifiers. When used in this manner
be close, nor that the antenna be ad-
Iusted to resonance. Far better re-
suits will be obtained If both these
are actually reversed,
!. e., loose coupling and no attempt
made to secure resonance in the an
emma system. There are good reasons |
or this somewhat radical departure /
rom generally accepted principles. t
Keep Resistance Low.
All resistance should be kept at the {
owest possible value in the input cir I
uit. Some of these, such as con- .
uctor resistance, resistance due to
attributed capacity in winding form,
esistance due to delectric absorption,
to-, are readily handled so that their u
eduction Is not so difficult. But when
MS input circuit is coupled to the an +
emma system we find an additional re-
stance, namely, one of energy alb
Drption. When two circuits are con-
ected so that one is transferring en-
-gy to the other, the primary circuit 81
,nds to reabsorb energy from the sec 81
ndary. This amounts to a reduction s.
? energy received in the second cir 81
lit and the net result Is an apparent Il
crease in the secondary resistance 10
urther we find that more nearly the re
'imary circuit approaches resonance
It'll the secondary circuit the greater
e retransfer of energy, hence the
eater resistance from this effect.
his effect Is more pronounced the
arer the primary is in resonance
til the secondary and the closer the
tual coupling between these circuits.
1t at once becomes evident that II
: are to cut down the resistance
our secondary circuit we must avoid
our antenna TO the input sW
cult and likewise keep the coupling frt
lductive and capacitive, by the way) tn
tween these two circuits at MINI tn
I'm. 1t does not follow that we can to
to an extreme looseness Of coupling, ha
r be too far off resonance In our Ing
tenna system, as this would lead to ne
luction of energy in our input cir or
It. However, 1t has been deter to
ned that II certain near-resonant ! do