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Патент USA US2406720

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Aug. 27, 1-946.
Filed March 1'7’, 1943
g. #4
* r/'9.'32 2% 3 BY "22m
T’atented Aug. 27, 19746
' 2,406,720
Carol Jan van Loon, Eindhoven, Netherlands, as
signor to Hartford National Bank and Trust
Company, Hartford, Conn., as trustee
Application March 1'7, 1943, Serial No. 479,465
In the Netherlands March 8, 1941
1 Claim.
(Cl. 171-242)
The invention relates to self-induction coils
whose self-induction may be adjusted by a core
of magnetic material which is slidable in the ?eld
of the coil, said coils being referred to herein
after as “slidable~core coils.” These slidable
core coils are utilized inter alia in radio-receiv
ing sets in which they may form part of the
tuning means.
In practice it is often desirable that the value
frequency difference will be obtained not only
at the limits of the respective frequency ranges
of said circuits but also at one or more interme
diate points.
In the drawing:
Figs. 1 and 2 are curves showing conditions of
tracking and mistracking between a pair of per
meability tuned circuits at various positions of
adjustment of the tuning cores. Fig. 3 discloses
of the self-induction of the slidable-core coil as 10 a known construction for effecting inductance
a function of the position of the iron core should
variation in coils. Fig. 4 discloses a coil and core
have a predetermined course. Such is the case
combination, in accordance with the present in
inter alia in superheterodyne receivers if in the
vention for effecting a predetermined inductance
tuning circuits use is made of slidable-core coils.
variation. Figs. 4a and 4b are cross-sectional
As is well-known, with a superheterodyne re 1
ceiver there must exist over the whole of the
wave range a constant difference in frequency
views taken respectively, on the lines a,—a and
and a capacity in parallel with the variable con
whereas the curve 11 indicates the course which
really occurs if no particular steps are taken. In
order to obtain the desired course it is necessary,
b—~b of Fig. 4 and Fig. 5 discloses curves showing
the improved tracking relation obtained with the
between the tuning of the oscillator circuit and
present invention.
that of the preceding circuits so that, given a
Figure 1 shows the course of the divergence d
determined course of the tuning of the preceding 20 in kilocycles as a function of the stroke S in milli
circuit, a determined course of the tuning of the
meters of the slidable core in the absence of pre
oscillator circuit is ?xed.
cautionary measures for effecting tracking at
If the tuning is effected by means of a ?xed
an intermediate point.
inductance and a variable condenser, a substan
In Figure 2 the curve I indicates the desired
tially constant difference in frequency may be ' course of the self-induction L of the coil as a
obtained by connecting a capacity in series with
function of the stroke of the core in millimeters
denser. These additional capacities should pref
erably be formed as trimmers in order to ensure
that adjustment is possible.
If, however, the tuning is effected by means of
as ensues from Figure 2, to increase the slope
of the self-induction variation at the beginning
of the stroke and to decrease this slope at the
end of the stroke.
a variable inductance and a ?xed capacity, as is
the case with the use of slidable-core coils, it
would be necessary to try in a similar manner to
According to British patent speci?cation 410,217
obtain the desired result by connecting an addi 85 it is known to increase the slope of the variation
tional inductance in series with and an addi
of the self-induction of a slidable core by caus
tional inductance in parallel with the variable
ing a core of copper and a high-frequency iron
inductance. This leads, however, to an expen
core to slide, the one after the other, through
sive and complicated system of connections.
the coil. A construction suitable thereto is shown
If these additional inductances are omitted, it 40 in Figure 3.
is possible to obtain the correct difference in fre
In this ?gure l represents a coil, 2 is a core of
quency between the oscillator circuit and the pre
high-frequency iron and 3 is a rod or tube of
ceding circuits only at two points of the wave
conductive material, for example, copper. Upon
range, for example in the neighborhood of the
assuming that the initial position is that in which
highest and of the lowest frequencies; in the in
the whole of the core 3 is within the‘ coil and the
termediate region there is produced in this case,
whole of the core .2 is outside the coil, the self
however, an inadmissibly large divergence from
induction of the coil increases, when both cores
the desired difference in wave-length, which di
are caused to slide from the right to the left, to
vergence may amount in the middle of the inter
a higher extent than would be the case with the
mediate wave-length range up to 60 or 70 kilo 50
use of a slidable core since the iron core exerts
its action in a coil portion which steadily in
It is, therefore, the main object of the present
creases and, in addition, the copper core 3, which
invention to improve the tracking relation be
acts as a short-circuited winding, encloses a
tween the signal frequency and oscillator circuits
steadily decreasing number of lines of force.
of a superheterodyne receiver so that the correct 55
Since, however, by utilizing this construction it
is possible to increase the slope of the increase of
the self-induction but impossible to decrease this
mentally and may have in a determined case the
shape indicated in Figure 4 which diminishes in
slope, the use of this form of construction cannot
cross-section from each end inwardly toward
give here the desired result.
According to the present invention, in order to
body of
to slide,
the coil,
the center.
Otherwise, in constructing such a slidable-core
coil the fact has to be taken into account that the
presence of the copper body 4 necessitates an
increase of the number of turns or again an in
crease of the permeability of the slidable core in
order to be able to obtain the same value of the
maximum self-induction. Care should be taken
being so chosen that the desired course of the
in this case to ensure that the minimum value of
self-induction is obtained.
the self-induction does not increase, which may
be effected by increasing the permeability of the
core. In the absence of the copper strip accord
ing to
invention the course of the self-induc
obtain with slidable-core coils a predetermined
course of the self-induction as a function of the
stroke of the core there is provided a
conductive material which is caused
jointly with the core, into the ?eld of
the shape of the body of conductive
In one form of construction according to the
invention the body of conductive material is
preferably provided on the core itself or, if the
core is made of pressed material, it is pressed
jointly with the core to form a mechanic unit.
The invention will be explained more fully with
reference to Figures ll and 5 of the accompany 20
ing drawing.
Figure 4 shows a slidable-core coil of cylindri
tion curve would become steeper over the whole
of the range; by providing the copper body the
course of the curve on the desired portions is
restored to the desired slope.
What I claim is:
A. variable inductance device comprising a
coil of the solenoid type, a core movable axially
cal shape wherein the coil body is denoted by I,
the turns of the coil by 2 and the slidable core by
within the coil and adapted upon movement from
In Figure 5 the course of the self-induction L 25 a position outside the coil to a position fully
as a function of the stroke of the slidable core
contained within the coil to vary the inductance
is shown by curve I.
of the coil in a predetermined manner as a func
If for some reason or other it is desired that
tion of the core‘travel, said core consisting of a
the curve indicating the course of the self-induc
substantially cylindrical body of magnetic mate
tion should have a more horizontal course at the 30
rial and an insert of non-magnetic conductive
beginning and at the end but a steeper course in
the middle, this may be achieved, in accordance
with the invention, by providing on the core 3 a
body or insert 4 of conductive material which
has a determined shape. The conductive mate
rial may be for example, copper. The shape of
this body or insert may be determined experi
material embedded in the surface of said body,
the surface of the insert being coextensive with
the body, and said insert diminishing in
cross~section from each end inwardly toward the
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