Radio Broadcast - 1925, February - 113 Pages ... - VacuumTubeEra

What Reflex
Means
How One Tube is Made to Do the Work of Two Problems of Reflexing and
How They Are Solved Various Uses of Reflexing Another Family Tree Diagram
BY JULIAN KAY
TH IS article in this series of informative articles about some of the technical phases
of radio written in a decidedly non-technical fashion deals this month with the use
of reflexing. The patent on the reflex system dates back to February, 1913, when
Schloemilch and Van Bronck had their application approved. There are few who
have heard something about radio who haven't also heard the word "reflex."
Many radio listeners want a good review of reflexing and that is just what Mr.
Kay has done. Other articles in Mr. Kay's "What's In a Name" series have
discussed the various classes of receivers in use, radio-frequency amplification, audiofrequency
amplification, and the super-heterodyne. THE EDITOR.
THE
old song that "every little bit
added to what you've got makes just
a little bit more" applies nowhere
in radio quite so well as in this reflex
business. Given a small pocket book and a
long way to go via radio, what is one to do
The answer is to add just the little bit more
and that is what reflexing effectually does.
In the preceeding articles of this series, the
various forms of detectors and amplifiers havebeen
analyzed as separate units. Some mention
has been .made* of complete receiving
equipment such as the neutrodyne and the
heterodyne, both of which are really efficient
combinations both of detectors and amplifiers.
It is in the latter class of complete receivers
that the reflex lies.
The Family Tree diagram on page 672 shows
the place of the reflex among radio circuits.
It is a combination, a sort of trick combination
if
you will, of a detector and two amplifiers.
The reflex idea may be extended to other complete
receiving systems, such as to the neutrodyne,
for example in the Fada 160, or to the
super-heterodyne as in the Radiola.
The main idea of reflexing is to do away with
one vacuum tube, to make one do the work of
two. And while it is fairly simple to build a
detector and an amplifier as separate units,
it is a more difficult problem to build a reflex
that works as well as the more complicated
apparatus it replaces. Unless the reflex is
correctly constructed from tried and true
methods it will lose as much or more than it
gains a state of affairs that is not true economy.
Fig. shows the i general scheme. Energy
from the output of the circuit is fed back into
the input so that the apparatus involved does
double duty. The necessity for the frequency
changer lies in the fact that one cannot perform
this feeding back stunt without having
something happen a something usually made
evident by howls and groans. In other words,
the amplifier oscillates.
A SIMPLE FORM OF REFLEX
A SIMPLE form of reflex with which everyone
is familiar is the well known "tickler"
feed back affair. In this case, shown in Fig. 2,
some of the radio frequency energy is placed in
the input again by means of a coil inserted in
the output or plate circuit. If the tickler is
brought near enough to the secondary coil, the
system oscillates. The remarkable amplification
that results just before oscillation takes
place is well known.
I f the same scheme could be applied to audiofrequency
amplifiers, much more amplification
INPUT