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Патент USA US2119333

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May 31, 1938.
Filed May 22, 1936
F .
BY vfq 4 ~
Patented May 31, 1938
Friedrich Kreienfeld, Berlin, Germany, assignor
to Telefunken Gesellschaft fiir Drahtlose Tele
graphic in. b. 11., Berlin, Germany, a corpora
tion of Germany
Application May 22, 1936, Serial No. 81,146
In Germany July 19, 1935
2‘ Claims.
(Cl. 250-20)
A gradually variable coupling can be easily ob
tained by arranging two coils movable towards
each other. If in such an arrangement very
small coupling degrees are to be attained, it is
necessary to space the coils very far apart.
In modern radio ampli?ers such a condition
is very disadvantageous, since it is contrary to
the desire to reduce the size of the ampli?er
structure. On the other hand, it is“ however de
sirable to provide a coupling that is variable
within wide limits so as to obtain a possibly wide
control range, for example, for purposes of vol
ume control.
This invention provides means to obtain a
practically complete decoupling of two coils with
out departing thereby from the principle of a
small assembly.
According to the invention, a coil inserted in a
circuit is so arranged upon, or near the other coil
that it has a decoupling effect upon the ?eld of
the two coils. In many cases, the desired effect
can be‘ achieved with a single winding turn or
loop (for example a lead-in wire).
For a better understanding of the invention ref
erence is made to the accompanying drawing, in
Fig. 1 is a schematic circuit diagram of the in
put circuit of a radio receiver embodying the in
Fig. 2 shows an arrangement of the transformer
coils according to the invention, and
Fig. 3 is a circuit diagram showing the use of
a lead wire as a reverse turn coil.
In Figure 1 this variable coupling is utilized in
an antenna coupling of a receiver.
Numeral I
designates the antenna, 2 is the antenna coil pri
mary, 3 represents the tuned input circuit of the
tube 4 with the secondary coil 5 and variable
condenser 6. Numeral ‘I designates the third coil
according to the invention and which is inserted
in the antenna circuit, but disposed upon, or near
the coil 5. The angular direction of winding of
‘I is so chosen that the coil produces a voltage in
5 whose phase is displaced 180 degrees from that
produced by coil 2.
In Figure 2 the coil arrangement for the cir
cuit of Figure 1 is schematically represented. 2
denotes the antenna coil, 9 the supporting arm
therefor which is rotatably mounted on shaft l0,
50 5 represents the secondary coil, 8 is a high fre
quency iron core, 1 designates the auxiliary wind
ing connected in series to the antenna coil 2 as
by a lead l5 and rigidly fastened with coil 5 in
the chassis.
To further elucidate the idea of the invention,
Figure 3 shows the two coupling coils turned at
180 degrees to each other. This turning takes
place about the shaft Hi. In this ?gure, 2 is
again the antenna coil, 5 is the tuned circuit coil, 5
1 is the turn or loop formed by the earth lead
of coil 2, II is the connection from the antenna
to the antenna coil. As indicated in Figure 3, the
coil 2 is wound in the clockwise direction. The
same direction pertains also for the loop 1 con 1O
nected to ground at point i2. But it should be
borne in mind that the coil 2 is shown swung
about the shaft ill by 180 degrees, so that in
fact the winding direction of 2 is opposite to that
of ‘I.
In addition it must be pointed out that once
the position of coil 1 relative to coil 5 is chosen,
this position remains constant. Hence, no cou
pling change occurs between ‘I and 5 upon the
variation of the coupling between coils 2 and 5.
In a closely coupled state, the counter coupling
produced by ‘I is practically negligible, since the
winding or turn ratio between coil 1 and coil 2
is usually less than 1/50. Thus a limitation of
the control range towards high coupling degrees
practically does not occur.
Having described my invention, what I claim
as novel and desire to secure by Letters Patent
1. In combination, a radio device having a res
onant input circuit comprising a transformer
secondary winding having a plurality of turns, a
single turn primary winding ?xed with reference
to said secondary winding, a second primary
winding connected in series with said single turn :
winding and having its turns wound in the op
posite direction to said single turn, means for
varying the coupling between said second
primary winding and said secondary winding,
and a. source of radio frequency signal currents
coupled to said primary windings.
2. In combination, an antenna, a transformer
secondary winding, a primary winding coupled
to said secondary winding, 21. lead connecting one
end of said primary to said antenna, a lead con
necting the other end of said primary to ground,
said last named lead being formed into a loop
of at least one turn which encircles said sec
ondary winding and the voltage induced in said
secondary by said loop being opposed to that in
duced therein by said primary winding and means
for changing the degree of coupling between said
primary and secondary windings.
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