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Патент USA US2122562

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July 5, 1938.
w. F. EWALD
2,122,562 ‘
TUNING INDICATOR CIRCUIT
Filed July 23, 1936
A. F. AMPLIFIER
Z'IDDET
WOLFGANG
INVENTOR
F.
EWALD
ATTORNEY
Patented July 5‘, 1938
v2,122,562
UNITED. STATES PATENT OFFICE
2,122,562
TUNING INDICATOR CIRCUIT
Wolfgang F. Ewald, Berlin, Germany, assignor to
Telefunken Gesellschaft fiir Drahtlose Tele
graphie m. b. 11., Berlin, Germany, a corpora
tion of Germany
‘Application July 23, 1936, Serial No. 92,066
In Germany July 26, 1935
7 Claims.
It is known that di?iculties are encountered
in attempting an accurate tuning of a receiver
to a carrier wave especially in receivers with
fading control, in which owing to the control
5
performance the volume does not decrease when
tuning to the side bands, while incomplete tun
ing is noted only by a distortion of the tone. The
customary optical indicating instruments have the
(Cl. 250-20)
to the carrier wave. This is accomplished in
that a corresponding bias is applied to one of
the grids f of the oscillator, and this is derived
from the intermediate frequency part of the re
ceiver. The bias is such that it suf?ces only for
rendering the oscillator inoperative, at tuning
to the carrier wave. To facilitate this, a control
‘ resistor r is inserted in the cathode lead of the
disadvantage that they do not always afford an
oscillator 11 and by means of which it is possible
10 easy‘ tuning to the optimum, the more so since
to adjust at will the oscillation tendency of this
tube.
Obviously, the bias applied to the grid of the
it is necessary simultaneously to view the station
dial as well as the tuning instrument. Devices
have already been proposed to render the receiver
inoperative automatically at inexact tuning; for
instance, by means of a circuit with very steep
characteristic and placed in parallel to the inter
mediate frequnecy part, which supplies, when
resonance occurs, to a subsequently connected
tube that is normally blocked, a counter poten
20 tial by which the blocking is released, and thereby
reproduction made possible. However, the means
required for this device are considerable, so that
this device could hitherto not be put to practice.
In accordance with the present invention it is
25 proposed to produce either a constant, or vari
able steady, note, which is silenced only when the
receiver is exactly tuned to the carrier wave.
Hence at incorrect tuning to any carrier wave
the tone is heard in the manner of a busy signal,
30 but which disappears at the correct tuning to any
desired transmitter, thus preventing the bearer
from being unaware of the false tuning.
The subject matter of the invention will now
be elucidated with reference to the circuit dia
35 gram shown in the ?gure by Way of example. A
conventional superheterodyne receiver is shown,
the second detector supplying AVC bias. The
additional elements consist, for instance, of a
tube a serving as oscillator, and having a grid
40 circuit a tuned to the intermediate frequency of
the superheterodyne receiver. At the tuning of
the receiver, a beat note is produced between the
oscillations of the oscillator a and the interme
diate frequency energy, whereby this note be
45 comes the lower the more the tuning approaches
the carrier wave of a transmitter. At exact tun
ing to the transmitter, the intermediate fre
quency will attain its required value and hence
exact conformity to the frequency of the oscil
50 lator a, so that the beat note disappears.
Since, however, at small voltage variations,
differences between the two frequencies, although
they may be small, and hence beating can pos
sibly not be avoided, it may be necessary to ren
55 der the oscillator 11 inoperative at sharp tuning
tube a used for blocking, depends upon the am
plitude of the tuned carrier wave. However,
especially when using fading control, it is pos
sible immediately to adapt the arrangement in
such manner that also in case of weak carrier
Waves, the oscillator will be disconnected with
out causing a premature disconnection at strong
carrier waves.
20
It will not always be appropriate to have the
oscillator a proper oscillating on the intermediate
frequency. As a rule it will rather be of advan
tage to utilize a fraction or a multiple of this fre
quency, and to utilize the upper harmonics of the
fundamental oscillation for the production of the
note.
What is claimed is:
1. In combination with a wave transmission
system, means for detecting waves transmitted
through the system, means for impressing waves
of the same frequency as the transmitted wave
frequency upon said detecting means so as to
provide beat energy when said transmitted waves ,
change in frequency from the impressed Wave
frequency value, means for deriving a voltage
from the transmitted waves whose magnitude
varies directly with transmitted wave amplitude,
and additional means for controlling said im
pressing means with said derived voltage in a
sense to render the impressing means ineffective
when said derived voltage is a maximum.
2. In combination with a wave transmission
system, means for detecting waves transmitted
through the system, means for impressing waves 45
of the same frequency as the transmitted wave
frequency upon said detecting means so as to
provide beat energy when said transmitted waves
change in frequency from the impressed wave
frequency value, means for deriving a voltage
from the transmitted waves whose magnitude
varies directly with transmitted wave amplitude,
additional means for controlling said impressing
means with said derived voltage in a sense to
render the impressing means ineffective when 55
2
2,122,562
said derived voltage is a maximum, and means
for controlling the wave transmission e?iciency
to said detecting means with said derived voltage
put circuit, a second detector tube and a local
oscillator tube operating at the frequency of the
intermediate frequency energy, means for im
in a sense to maintain the wave amplitude at
pressing the local oscillations upon a point be
tween the input circuit and the detector tube, 5
the latter uniform.
3., In a superheterodyne receiver of the type
including an intermediate frequency ampli?er, a
second detector and an audio output network, the
method of indicating accurate tuning of the re
10 ceiver which includes producing local oscillations
of a frequency equal to said intermediate fre
quency, feeding said oscillations to the second
detector, deriving a unidirectional voltage from
the intermediate frequency energy, and employ
15 ing said derived voltage to prevent said oscilla
tion production when said intermediate energy
and means responsive automatically to an in
crease in amplitude of said intermediate energy
at resonance, for rendering the oscillator tube
inoperative.
‘
6. In a superheterodyne receiver, at least one
intermediate frequency ampli?er, a second de
tector, a network tuned to the intermediate fre-~
quency coupling the amplifier output electrodes
to the detector, a tube connected to produce os
cillations of said frequency, means for impress 15
ing the oscillations on a point of the network,
is of a frequency equal to the local oscillation fre
a circuit deriving a direct current voltage from
quency.
intermediate frequency energy which varies di
rectly in amplitude with the latter, and means for
_
4. In a radio receiver which includes a signal
20 ampli?er and a detector whose input circuit is
coupled thereto, means for tuning the ampli?er
to different stations in a‘ tuning range, an accu
racy tuning indicator device comprising a local
oscillator circuit connected to produce oscilla
tions of a frequency equal to the frequency of the
signal energy impressed on the detector input
circuit, means impressing said oscillations on
said detector input circuit whereby a beat note
applying the voltage to an electrode of the oscil
lator tube in a sense to render the same inopera
tive.
7. In a superheterodyne receiver, at least one
intermediate frequency ampli?er, a second de
tector, a network tuned to the intermediate fre
quency coupling the ampli?er output electrodes
to the detector, a tube connected to produce os
cillations of said frequency, means for impressing
the oscillations on a point of the network, a
is produced by the detector when the detector
input energy differs in frequency from said oscil
lation frequency, an automatic'volume control
circuit connected between said detector input cir
cuit and ampli?er, and a connection between the
circuit deriving a direct current voltage from in
termediate frequency energy which varies di
rectly in amplitude with the latter, means for'
applying the voltage to an electrode of the oscil
control circuit and said local oscillator for ren
dering the latter ineffective at the desired station
lator tube in a sense to render the same inopera
tive, and additional means for applying the di
settings of the tuning means.
rect current voltage to an electrode of the ampli
?er in a sense to reduce the gain thereof.
.
WOLFGANG F. EWALD.
5. In a superheterodyne receiver of the type
including an intermediate frequency energy in
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