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Патент USA US2114615

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K. scHLEslNGER
SUPERHETERODYNE RECEIVER
Filed Jan. 6, 1957
l
ÈÄMQÜÜ
2,114,615
Patented Apr. 19, 1938
UNITED STATES PATENT OFFICE
2,114,615
SUPERHETERODYNE RECEIVER
Kurt Schlesinger, Berlin, Germany
Application January 6, 1937, Serial No. 119,193
In Germany January 13, 1936
5 Claims.
The present invention relates to receivers em
ploying locally generated oscillations and its main
object is to prevent disturbing radiation of. local
(Cl. 2250-20)
scribed with reference to the accompanying
drawing, Figs. 1-3.
Fig. 1 shows the mixing stage of a super
,heterodyne receiver using the neutralizing cir
cuit according to the invention.
The radiation of local oscillations in super
5
Fig. 2 shows a schematic diagram of the
heterodyne receivers is interfering even in the
case of comparatively long waves, but in the case neutralizing circuit of Fig. 1, and
Fig. 3 shows a modification of the circuit of
of shorter waves it is considerably amplified.
Specially designed tubes, so-called mixing tubes, Fig. 1.
vIn Fig. 1 there is shown a typical mixing tube
4‘10 are known in practice, in which it is possible to
eliminate capacitative couplings between the circuit directly connected to an aerial. The mix
ing tube I, as Well known, is divided by an inner
local oscillator and the receiving channel by in
screening means 2 into two separate tube systems,
ternally fitted screening means between the os
cillator system and the mixing system. The the one of which acts as oscillator system and
15 shorter the wavelength, however, the greater are the other as mixing system. The received signals
the capacitative currents which flow by way of are conducted to th-e latter by way of a first grid
oscillations.
>
the remaining coupling capacities still present,
which latter, generally speaking, are already
within the order of .1 cm. A further reduction
of these capacity Values is hardly possible, and a
capacity of this magnitude is already fully suf
ficient for interfering radiation. The circuits
are using screen grid tubes, such as have alr-eady
been proposed for these purposes. Such circuits
must also necessarily fail more and more pro
las ceeding from a critical short wave length down
wards. In addition there is the fact that the
gain in amplification of the preliminary tubes
also sinks with the wavelength, and the economic
efficiency of the tube will be reduced more and
more.
Remedy has already been obtained according
to the invention in an earlier application
(Schlesinger Ser. No. 67,343, filed March 5, 1936)
ment or non-dissipative air condenser).
If the
reception is to take place with full volume of
sound, it is necessary for the cathode 8 also to
be dynamically earthed by way of a resistance,
which must be small in relation to the grid
neutralized by a special neutralization. The de
tails of this method, which is not entirely simple
the neutralization of the radiation greatly de
to adapt to high frequencies, were then set forth
in a later application (Schlesinger Serial No.
teriorates or ceases, or in certain circumstances
the radiation is even increased, at the same
moment. If on the other hand the cathode 8
¿o 72,314, April 2, 1937) . In the method therein set
forth the cathode of the receiving system is con
nected with earth only by way of a choke and
accordingly participates in the received oscilla
tions. It is certainly possible by means of the
ß method therein set forth to obtain a very good
compensation of the radiation, which also re
mains to a certain extent independent of the
frequency, but at the same time the sensitivity
of reception is reduced to a comparatively large
50 degree.
In the present application the two require
ments, freedom from radiation and the main
tenance of the full sensitivity of reception, are
fulñlled.
55
a condenser 9 (non-dissipative ceramic embodi
cathode capacity I0 of the tube between the re
ceiving grid 3 and the cathode 8. If the cathode l 35
8 is earthed in direct fashion it will be found that
r35 by the fact that the detrimental capacity is
1
3. The aerial 4 or the feed line 5 to the aerial
is in the present case inductively coupled by
way of a transformer 6. In order that powerful
oscillations will be produced the cathode, grid and
anode must be connected with one another in the 20
oscillator system without interfering phase shift
ing and by means of short leads. This is prefer
ably accomplished by means of a twin condenser
la, 1b, the middle electrode of which is connected 5
with the cathode 8. The grid circuit of the re
ceiying grid 3 is dynamically earthed by wayy of
'
Embodiments of the invention will now be de
is applied to earth by way of a choke ll, there
is obtained an admirable neutralization', but‘
the reception is lost, as the resistance of I I is
greater than the resistance of the grid-capacity
I0, and a receiving current of such negligible 45
kind flows from 6 to the grid path that a suf
ficient receiving potential is unable to build up
between grid and cathode.
In Fig. 2 there is proved the reason for this
remarkable relationship between cathode earth 50
ing and neutralization circuit which latter rep
resents a bridge-circuit. The neutralization is
performed as already described in the earlier
applications by a compensating condenser I2, a
small adjustable capacity of the order of the 55
2
2,114,615
detrimental capacity with the assistance of the
opposite-phase potential which is available at the
anode of the oscillator system. In Fig. 2 the
capacities having special bearing have been par
ticularly indicated. The receiving grid 3 is on
the one hand in capacitative coupling with the
mixing grid :I4-between the two there exists the
detrimental capacity I3 passing through the
io
screening grid of the hexode,-and on the other
hand there is applied to the receiving grid 3 the
neutralization potential b-y condenser I2, which is
adapted in its order of magnitude to the value ES.>
rI'he operating potentials of this bridge arm are
derived from the rotating plate condensers 1a, 'Ib
of the local oscillator, which owing to their size
ensure that -the potentials at the points A and G
are of opposite phase. Between the grid 3.and
the chassis and in surrounding conductors and
are very diiîicult to control it is not desirable to
connect the three poles of the oscillator direct to
earth. A very good neutralization, however, may
be immediately accomplished if the earthing of 8 Ol
is performed with resistances as highly ohmic as
possible. By reason of the stated dimensioning of
the condensers I'I and I8 and simultaneously
using a choke I I, which is to be regarded as high
ly ohmic in the wave band employed, there is no
loss in the volume of reception, as the resistance
of the total of Il and I8 is smaller than the
resistance of I0. The powerful currents of the
oscillator, however, do not flow by way of the
differential to earth and accordingly do not cause 15
any interfering coupling.
The arrangement of Fig. 2 has the disadvan
the cathode 8 there is a tube capacity I0, which ' tage that two bridges have to be equalized at the
is fairly large in practice (approximately 20cm.
including leading-through capacity). ' So long as
the cathode 8 is earthed by way of a choke II
it is a simple matter by the balancing of I2 to
raise the receiving grid 3 and the cathode 8 to
the same potential.
There is, however, no re
Y25 ception, as the resistance of I l is greater than
that of lil.
Now there exist between the'ter
minals G and A of the oscillatory system earth
capacities I5 and I6 of general, greatly varying
value.v rThe bridge: la, 1b, I5, I6 is, therefore,
30 generally speaking, not in equilibrium.
It is ac
cordingly impossible to connect the cathode point
8 to earth without influencing the values of 1b, 1a,
and in this way the bridge first balanced is like
wise varied and the compensation of the radiation
135
is destroyed.
’
Y
The arrangement according to Fig. 1, therefore,
same time, viz., the neutralization bridge I3, I2
and the earthing bridge I'I, I8. The arrange 20
ment of Fig. 3 is free of such disadvantage, in
that only a single equalizing operation is neces
sary. Condenser I2 is eliminated and its func
tion is undertaken by the already existing con
denser IIJ by so adjusting the differential con
25
denser I‘I, I8, I9, that cathode 8 is not accu
`rately at earth potential, but has a small oscil
lation amplitude in reverse phase to the mixing
grid I4 and earth. If the. rotor I9 of the dif
ferential condensers Il and I8 is displaced in the 30
manner shown in Fig. 3 in relation to its neutral
position, so that the capacity on the grid side is
somewhat greater than the capacity I8 on the
anode side,’the cathode 8 passes into the correct
potential range useful for compensation pur
poses, in which it is capable, by way of the
in accordance with Fig. 2, represents together
with the part-capacities against earth’a double
grid capacity I0, of balancing out the receiving
grid 3 and accordingly the aerial 4 against radia
bridge-circuit.
tion. There is no loss with respect to the sensi
tivity of reception, Yas the received currents, pro- _
According to the invention a bal
ancing of the two bridge-circuits between tuning
condenser and aerial grid on the'one hand and
1between tuning condenser and earth on the other
hand is performed simultaneously, and in this way
there is rendered possible an earthing of the
45 cathode 8 and together therewith a full sensi
tivity in respect of the reception together with
the compensation of the radiation. In accord
ance with the invention there is arranged a »dif
ferential condenser having thecapacities Il and
50 I8 which may be varied by the rotary electrode
I9. This differential condenser is lying in par
allel to the oscillatory circuit and the two in
definite inherent capacities I5 and I 6. The value
of the two capacities is chosen in the order of
Ul Gl magnitude of the capacity I0 between receiving
grid and cathode of the mixing tube for example
equal to or greater than said capacity I0 so that
the impedance of the earth connection -via the
differential condenser forming a capacitive par
60 allel connection is small in comparison with the
impedance of the grid-cathode path of the mix
ing electrode-system. Further this capacity I0
is made as small as possible, for example by using
a tube having the receiving grid separately led
out of the glass bulb. The junction point of the
condensers ‘Ia and 'Ib may be adjusted to have
earth potential by corresponding adjustmentof
the differential condenser with its capacities VI'I
and I8. After this has been done,- the cathode 8
in itself could be earthed in direct-fashion with
out the previously adjusted neutralization I2, -I3
being destroyed, and a full volume of reception
would take place.
It has been found in practice that in the case
of the eddy currents which flow in the metal> of
ceeding from 3, are able to find their way to`
earth without resistance by way of the parallel
connection of the series 1b, I1 and 1a, I8, since
in accordance with the invention the parallel
connection of I'I and I8 should be large in rela- -_
tion to I0.
,
It has been found that a circuit according to
Fig. 3 may be adjusted very well by the turning
of one single armature I9 of the differential con
denser connected with earth. At the same timev 50
it appears, however, that it is not immaterial at
what point >the earthing of the armature I9 is
connected. The stated stray currents in the chas
sis are apparently the reasons for this indefinite
nature of the earthing point I9. To render also,V
these ineffective it is proposed to enclose the
oscillatory circuit', including its coil 25 and the dif
ferential I'I and II8, in a screening casing 20,
which may also include the receiving tube I. This
casing should be in direct connection with the
rotor armature I9 of the differential condenser
I‘I, I8. It should, however, be insulated itself
-against the earth of the chassis 2l and connected
therewith only by means of a single lead 22. In,
this way it is accomplished that the comparatively!
powerful induced currents flowing in the wall of
the screening means 29, together with their ap
pertaining drop in potential, do not enter the
circuits of the compensation bridge according to
Fig. 34
'1"'70
VA ñnal source of error is caused by the oscil
lator tube itself. The oscillator tube is connected
with its anode-cathode path in parallel with the
condenser portion 1a, whereas only the grid-cath
ode path is in parallel with the other condenserî
12,114,615
portion 1b. Now in the case of three-electrode
tubes the inner resistance of the anode path
is comparatively low, whilst the grid resistance
of these tubes is very high. There accordingly
results an interference with the freedom of phase
shifting of the condenser 1a, 1b. .The procedure
of compensating in accordance with the inven
tion may be supported by the following addi
tional means:
10
l. Inclusion of a parallel resistance 23 between
grid-condenser portion "ib (Fig. 3). This re
sistance would simulate, and accordingly render
ineffective, the phase shifting in the grid circuit
caused by the tube.
15
‘
'
2. Inclusion of a series resistance 2è inrthe lead
to the control grid (entered in Fig. 1). The effect
is the same as under 1.
.
3. The use of a four-electrode or five-electrode
tube as oscillator tube. Tubes of this nature have
20 in themselves a sufficiently large anode impedance
and do not interfere with the equilibrium of the
bridge. This method is superior to the others
mentioned as regards reliability, particularly
when exchanging the tubes, and is also largely
25 independent of the particular currents and biases
flowing in the tube.
I claim:
1. In a superheterodyne receiver means for
eliminating the interfering radiation of the locally
30 generated oscillations, a mixing tube including
a mixing electrode-system and an oscillatory elec
trode system, an oscillatory circuit connected to
the oscillatory electrode system, a neutralizing
circuit between said oscillatory system and said
35 mixing electrode system, said oscillatory circuit
consisting of a combination of two condensers
and an oscillatory choke and being connected be
tween the anode of said oscillatory electrode sys
tern and the cathode common to both said elec
40 trode systems, said cathode being connected to
the junction point of said two condensers, said
oscillatory circuit being connected with its two
poles having a potential of opposite phase to earth
by means of a, differential condenser the rotary
46 electrode of which being connected with earth
and being adjustable so that the potential of the
cathode is variable for balancing out the neu
tralizing circuit as regards the local oscillations,
the capacities of the differential condenser lying
50 in parallel connection to the oscillatory circuit
having a value equal to or greater than the capac
ity between receiving grid and cathode, the im
pedances of said earth connections via the dif
ferential condenser being small in comparison
55 with the impedance of the grid-cathode path of
the mixing electrode-system in respect to the
received frequency.
.
2. In a superheterodyne receiver means for
eliminating the interfering radiation of the locally
60 generated oscillations, a mixing tube including
a mixing electrode-system and an oscillatory elec
trode system, an oscillatory circuit connected to
the oscillatory electrode system, a neutralizing
circuit between said oscillatory system and said
65 mixing electrode system, said mixing electrode
system containing at least one screening grid,
said oscillatory circuit consisting of a combina
tion of two condensers and an oscillatory choke
and being connected between the anode of said
70 oscillatory electrode system and the cathode com
mon to both said electrode systems, said cathode
being connected to the junction point of said
two condensers, said oscillatory circuit being con
nected with its two poles having a potential of
u opposite phase to earth by means of a differential
3
condenser the rotary electrode of which being
connected with earth and being adjustable so that
the -potential of the cathode is variable for bal
ancing out the neutralizing circuit as regards
the local oscillations, the capacities of the differ
ential condenser lying in parallel connection to
the oscillatory circuit having a value equal to or
greater than the capacity between receiving grid
and cathode, the impedances of said earthcon
nections via the differential condenser being
small in comparison with the impedance of the
grid-cathode path of the mixing electrode system
in respect to the received frequency.
3. In a superheterodyne receiver means for
eliminating the interfering radiation of the lo
cally generated, oscillations, a mixing tube includ
ing a mixing electrode-system and an oscillatory
electrode-system, an oscillatory circuit connected
to the oscillatory electrode system, a neutralizing
circuit between said oscillatory system and said» .
mixing electrode system, said oscillatory circuit
consisting of a combination of two condensers
and an oscillatory choke and being connected be
tween the anode of said oscillatory electrode sys
tem and the cathode common to» both said elec
trode systems, said cathode being connected to
the junction point of said two condensers, said
oscillatory circuit being connected with its two
poles having a potential of opposite phase to
earth by means of a differential condenser the 30
rotary electrode of which being connected with
earth and being adjustable so that the potential
of the cathode is variable for balancing out the
neutralizing circuit as regards the local oscilla
tions the capacities of the differential condenser 35
lying in parallel connection to the oscillatory cir
cuit having a value equal to or greater than the
capacity between receiving grid and cathode,
the impedances of said earth connections via
the differential condenser being small in com 40
parison with the impedance of the grid-cathode
path of the mixing electrode-system in respect
to the received frequency, said neutralizing circuit
containing a variable condenser _for adjusting
45
neutralization of radiation.
4. In a superheterodyne receiver means` for
eliminating the interfering radiation of the lo
cally generated oscillations, a mixing tube includ
ing a mixing electrode-system and an oscillatory
electrode system, an oscillatory circuit connected 50
to the oscillatory electrode system, said oscilla
tory circuit consisting of a combination of two
condensers and an oscillatory choke and being
connected between the anode of said oscillatory
electro de system and the cathode common to both 55
said electrode systems, said cathode being con
nected to the junction point of said two con
densers, said oscillatory circuit being connected
with its two poles having a potential of opposite
phase to earth by means of a differential con
denser the rotary electrode of which being con
60
nected with earth and being adjustable so that
the potential of the cathode is variable for bal
ancing out they neutralizing circuit as regards the
local oscillations, the capacities of the differential 65
condenser lying in parallel connection to the
oscillatory circuit having a value equal to or
greater than the capacity between receiving grid
and cathode, the impedances of said earth con
nections via the diiïerential condenser being small 70
in comparison with the impedance of the grid
cathode path of themixing electrode-system in
respect to the received frequency, the rotary elec
trode of said differential condenser being adjusted
to such a setting that the cathode of the mixing 75
4
2,114,615
tube has a reverse phase oscillation of small
magnitude suiñcìent to neutralize the radiation of
ential condenser the rotary electrode of which
being connected with earth and being adjustable
local oscillations, the bias ofV said cathode being
conducted thereto by Way of a choke which has
so that the potential of the cathode is Variable
for balancing out the neutralizing circuit as re
a very high ohmic resistance with respect to the
received frequency.
gards the local oscillations, the capacities of the.
diñerential condenser lying in parallel ,connec
5. In a superheterodyne receiver means for ~tion to the oscillatory circuit having a value
eliminating the interfering radiation off the loi
equal to o-r greater than the capacity between
cally generated oscillations, a mixing tube includ
receiving grid and cathode, the impedances of said
10 ing a mixing electrode-system and an oscillatory
electrode system, an oscillatory circuit connected
to the oscillatory electrode system, said mixing
electrode-system containing at least one screen
ing grid, said oscillatory circuit consisting of a
15 combination of two condensers and an oscillatory
choke and being connected between the anode of
said oscillatory electrode system and the cathode
common to both said electrode systems, said
cathode being connected to the junction point of
20 said two condensers, said oscillatory circuit being
connected with its two poles having a potential
of opposite phase to earth by means of a differ
earth connections via the differential condenserv
being small in comparison With the impedance
of the grid cathode path of the mixing electrode
system in respect to the received frequency, the
rotary electrode of said differential condenser be'
ing adjusted to such a setting that the cathode' 15
of the mixing tube has a reverse phase oscillation
of small magnitude suñicient to neutralize the
radiation of local oscillations, the bias of said
cathode being conducted thereto by Way of a
choke which has a very high ohmic resistancel 20
with respect to the received frequency.
KURT SCHLESINGER.
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