2 2,250,277
United States were concerned, first because of the tuning by inductance variation with a movable
troublesome oscillations which such receivers ferromagnetic core, however, the inductance-to
produced and second because of the extreme diffl- resistance ratio may be maintained substantially
culty of adjusting such receivers for satisfactory constant, since insertion of the core provides a
performance. Both of these difficulties were due 5 simultaneous increase in the inductance and the
in large measure to the lack of uniformity over resistance of the resonant circuit as the fre
the tuning range, first in the resonant perform- quency decreases.
ance of the circuits then employed, and second in In my United States Patent No. 2,106,226, I
.the negative resistance or regenerative effect. disclose means for coupling two permeability
The demand for increased simplicity of control, 10 tuned resonant circuits, each of which has a sub
and finally for unl-control, drove the regenera- stantially constant ratio of inductance to high
tive receivers off the domestic market. frequency resistance throughout the frequency
Many attempts were made in the period from range, in such a way as to provide substantially 1921 to 1926 to provide a system of regeneration uniform over-all amplification and selectivity, which would be uniform in action over the range 15 The system described in that patent is intended of frequencies. These attempts failed, however, to operate without an appreciable degree of redue principally to the non-uniform performance generation. In accordance with my present inof the circuits then employed, with the result vention, however, I employ a pair of permeabilthat the art turned to completely non-regenera- ity-tuned resonant circuits which are. so detive types such as to so-called Neutrodyne re- 20 .signed and so coupled as to provide substantially ceivers, and to the superheterodyne method in uniform performance even though regeneration which the problem of high-frequency selectivity is utilized to greatly improve the performance of and gain was avoided by transposing all the sig- the system, nals to a fixed lower frequency. Thus my invention provides, for the first time,
It might be supposed that immediately upon 25 means for realizing the improvement in gain and
the advent of the uniform-performance per- selectivity obtainable by utilizing regeneration
meability-tuned circuit, it.would have been pos- without requiring additional vacuum, tubes or
sible to add regeneration according to any one manual controls, and without sacrificing the uni
of a number of well-known methods, to secure formity of performance which is readily secured
greatly improved performance uniformly over 30 by the use of movable ferromagnetic cores for
the tuning range. It may be shown, however, tuning. While the electrical circuit which I em
and many experiments have adequately verified ploy is superficially similar to .earlier arrange
the fact, that the regeneiative effect itself varies ments, it is pointed out that only by employing
materially with frequency* even when applied to components which are designed hi the manner to
a circuit of inherently uniform performance, and 35 be disclosed herein is it possible to realize the
my present invention is an arrangement in which greatly improved performance which my system
the highly desirable and advantages result of provides. As will be clear from what is to fol
substantially uniform performance in a regenera- low, my invention has the further advantage of
tive system is secured. :permitting the utilization of inductance devices
In my co-pending application, Serial Number 40 which do not, in themselves, provide substantial
339,697, filed June 10, 1940, I describe a system ly uniform selectivity over the frequency range,
employing unitary rather than coupled reso- without sacrifice of the highly desirable uni
nant circuits, and securing a regenerative or formity of performance which is a feature of the
negative resistance effect through the employ- invention.
ment of a vacuum tube whose only function is 45 It is an object of my invention, therefore, to
to produce this effect in a controlled manner. provide a high-frequency amplifying system
In arrangements according to my present inven- having a high degree of gain and selectivity which
tion, on the other hand, I employ coupled rather is maintained substantially uniform over a wide
than unitary resonant circuits, and I do not range of frequencies.
employ vacuum tubes solely to produce the re- so A further object of my invention is to progenerative effect, each of the vacuum tubes in vide simple and inexpensive means for improvthe present system acting additionally as a high- ing the selectivity and gain of a high-frequency frequency amplifier in the customary manner. amplifying system while at the same time main
In practicing my present invention I employ taining its performance substantially uniform one or more systems or stages each including an 55 over a wide range of frequencies, amplifying vacuum tube, a pair of coupled res- Still another object of my invention is to imonant circuits tuned by inductance variation prove the over-all resonant gain and selectivity with a ferromagnetic core movable relatively to of a pair of inductively tuned resonant circuits the inductance coil in each circuit, means for by a substantially uniform degree throughout a producing a decrease in the effective resistance eo wide range of frequencies, of the resonant circuit, and an arrangement for The attainment of these and other highly deutilizing this means in such a way that its re- sirable objects Is accomplished in accordance sistance-reducing effect varies in a desired man- with the invention in a manner to be brought ner with the frequency to which the coupled out more fully in the specification which follows, resonant circuits are tuned. I thus secure a de- 65 The invention will now be described by refergree of gain and selectivity over the range of ad- ence to the accompanying drawings, in which: justability which is much greater and more uni- . Fig. 1 is a schematic diagram of a tuned radioform than could be secured by the employment frequency amplifying stage in accordance with of the resonant circuits alone. the invention;
If a resonant circuit is tuned by capacitance 70 Fig. 2 is a graph showing the variation with variation, the inductance remains fixed and the frequency of some of the parameters of an emresistance increases with frequency. Thus the bodiment of the arrangement shown in Pig. 1; ratio of inductance to resistance varies widely and
over the frequency range, the circuit becoming Fig. 3 is a schematic diagram of a complete
increasingly poor at the higher frequencies. By 75 radio receiver embodying the invention.
