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

THE
LOSS STABILIZING R. F. CIRCUITS
greatest problem encountered in
design and construction of radiofrequency
amplifiers is the stabilization
of the system in which they are
incorporated the dissipating or nullifying of
the very strong tendency toward oscillations.
This tendency
is evident in each r. f. circuit,
but is most emphasized in (be second stage of a
two-step tuned radio-frequency amplifier or in
the second and third stages of a three-step
intensifier. In general, this tendency may be
combatted in two .ways by counteraction,
and by losses or absorption. Representative
of the first method is the neutrodyne and the
reversed feed-back systems, though in a narrow
sense, these systems may also be considered
as functioning through the introduction
of losses. The neutrodyne and reversed feedback
method are fairly well known and have
been described at length in various issues of
RADIO BROADCAST. The reader is
perhaps
less familiar with the loss systems, the advantages
of which
have been strongly
emphasized in recent
experiments in this
laboratory.
Loss methods of
stabilization are just
what the name suggests.
Losses are introduced
in the various
circuits, in which
there is
present an
oscillatory tendency,
of such a magnitude
that the surplus
energy which would
ordinarilv be utilized
In the R. B. Lab This Month
A good mt'thod for stabilising radio frequency
amplifiers. A comprehensive discussion
of simple and effective means of subduing undesired
oscillations in your tuned r. f . set.
This complete article is the outcome of a series
of experiments in our laboratory.
A brief dtscription of a six-tube de luxe
Roberts Knockout receiver, employing four
stages of resistance-coupled audio amplification.
Charging Edison element B batteries at
high charging rales.
Current carrying capacities of wire si^es
in small transformers.
Other items of helpful interest.
in starting and maintaining oscillations is
harmlessly dissipated. At first, the general
principle of the thing may appear all wrong.
The idea of deliberately introducing losses
seems contrary to the fundamental precepts
of radio. To-day, much effort is made to
reduce all losses in circuits through scientifically
designed coils and condensers. However,
losses can be made very useful and are quite
justified when properly used for stabilization.
In such arrangements the losses are so adjusted
that oscillations are just a little more than
stopped. This permits regeneration and a
practical maximum in signal strength, sensitivity,
and selectivity. (We write "practical"
because all of these qualities become still
more
intensified when the circuit is oscillating a
condition, however, in which enjoyable reception
is impossible).
Unfortunately, the introduction of even
losses over the entire tuning scale is an ideal
condition which, at its best, can only be ap-
The
proximated.
tendency to oscillate
increases in any
tuned circuit with the
The lower
frequency.
the wave (the higher
the frequency) the
greater is this tendency.
STRAIGHT ABSORPTION
I OSS stabilization
*-*
systems fall into
two classes that we
might describe as
"straight absorption"
and "differential ab-