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Патент USA US2127816

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Aug. _23, >1958.
P. F. G. HOLST ET AL
2,127,815
MULTICHANNEL RADIO -RECEIVING SYSTEM
Filed Aug. 29, 1936
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Patented Aug. 23, 1938
UNITED
2,127,816
TES PATENT OFFFI‘QE
2,127,816
MULTICHANNEL RADIO RECEIVING SYSTEM
Poul F. G. Holst, Oaklyn, and Loren R. Kirkwood,
Collingswood, N. J., assignors to Radio C‘or
poratìonlof America, a corporation of Delaware i
Application August 29, 1936, serial No. 98,444
l1 Claims. c1. 25o-_20)
in
The present invention relates to radio receiv
ing systems having two or more receiving chan
nels which may provide a combined output signal
as shown in our copending application Serial No.
pliñer channel therefor.
98,443, ñled August 29, 1936, for I-Iigh fidelity
a schematic circuit diagram of a radio receiving
radio receivers, and assigned to the same assignee
as this application.
A receiver to which the present invention may
be applied may comprise a pair of signal receiving
system embodying the invention `is shown in Fig.
1, and connections for the circuit of Fig. 1 with
110 and amplifying channels or circuits, one of which
is broadly responsive to received signals and the
other of which >is sharply responsive thereto, said
channels being further controllable to render the
broad channel effective only in response to signals
15 of a predetermined high amplitude whereas the
sharp channel is utilized for weaker signals.
In this manner, the fidelity or overall re
sponse of the receiving system improves with
increased carrier wave strength, giving a rela
20 tively high degree of fidelity for local radio pro
grams or in response to relatively strong modu
lated carrier waves.
'I‘he signal output from a
plurality of amplifying channels is preferably
applied to a common audio frequency amplifier
25 and loud speaker device for the reason that a
single amplifying channel results in desirable cost
reduction and for the further reason that the
sound from both channels preferably is derived
from a common loudspeaker output device with
30 out switching connections.
.
It is therefore an object of the present inven«
tion to provide an improved audio frequency or
second detector and audio frequency amplifier
system for a multiple channel radio signal re
35 ceiving system wherein the signals from either
The invention will be better understood upon
reference to the accompanying‘drawing` wherein
a high gain amplifier are shown in a similar
circuit diagram comprising Fig. y2. The scope
of the inventionïwill be pointed out in the ap 10
pended claims.
Referring to the drawing, the figure is a
schematic circuit diagram of a superheterodyne
radio receiving system embodying the invention..
This comprises two signal channels operating at 15.
radio or intermediate frequency, or both as
shown, with one receiving and amplifying channel sharply tuned and the other broadly tuned as
indicated. In -a superheterodyne receiver, each
channel may comprise a high or radio frequency
amplifying and tuning unit '5, a first detector 6
and an intermediate frequency amplifier l, con
nected to the same or separate signal'sources- as
indicated at 8 and 9 and tunable to the same or
differing frequencies.
25
In the present example, the superheterodyne
system indicated, includes also an oscillator I0 in
association with the first detector of each channel
and the signal channels‘furthermore, preferably
are provided with suitable automatic volume con 30
trol means II and I2 for controlling the signal
output in accordance with the strength of a re
ceived carrier wave, inany suitable well known
and understood manner. In the present system,
the automatic volume control means may be 35
channel may be combined in a common audio
effective to provide substantially constant signal
frequency amplifier and applied to a single loud
speaker device.
It is a further object of the present invention
amplitude with carrier wave strength variations
at the output of the intermediate frequency
amplifiers, whereby the second detectors are pro
vided with substantially constant signal strength. 40
4:0 to provide an audio frequency circuit for com
bining the signal output from a plurality of signal
channels in a radio receiving system wherein
either or both signal amplifying channels may
r function to amplify signals, and the output there~
’ from, separately or in combination, may be ap
plied to a common audio frequency amplifier and
loud speaker or other output device, without the
intermediary of switching means.
50
connection with a single audio frequency am
Each of the separate signal amplifying chan- ‘
nels is terminated in a second detector, the sharp
channel detector being indicated at I4 and the
broad channel detector being indicated at I5`
Both detectors may be of the same type, such as 45
diode rectifier devices, having cathodes It and
anodes I‘I, and are supplied with intermediate
frequency signal energy through suitable cou
pling transformers I8 preferably of the iron core
It is also an object of the present invention, to ’ fixed-tuned type.
` provide a signal channel mixing system for radio
receiving apparatus and the like, wherein the
transition from one signal channel to the other
may be made automatically in accordance with
„5 the strength of a received carrier Wave and in
The primary winding I9 of each transformer
is connected with the output circuit 'ZG of the
50
preceding intermediate frequency amplifier, while
the secondary 2 I, together with a shunt fixed tun
ing capacitor 22 provides a tuned input circuit for 55
2
2,127,816
the rectifier in which circuit the high potential
terminal 23 is connected with the anode. The low
potential terminal 24 of the input circuit for the
detector I4 is connected to the negative terminal
Ul 25 of a diode output resistor 26, the positive
terminal 2l of which is connected to the cathode
I6 and to ground as indicated at 28. Signals re~
ceived through the diode input circuit from the
preceding receiving system in the sharp channel
10 are applied to the diode anode I‘I and are rec
tif-led in the detector I4 and then appear as a
direct current potential across the resistor 25
between the positive terminal 2l and the nega
tive terminal 25, the terminal 25 being negative
15 with respect to ground or chassis 2B. The audio
frequency envelope or modulation component of
the signal also appears across the output resistor
26 between ground and the terminal 25. A suit~
able intermediate frequency by-pass capacitor 36
is provided across the resistor 26 to eliminate
therefrom any intermediate frequency currents
which may be present.
In a similar manner, the broad channel de
tector I5 is provided with a diode output resistor
25 3| having the positive terminal thereof 32 connected to ground or chassis 33 and to the cath
ode I6, while the negative terminal indicated at
34, is connected with the loW potential terminal
35 of the tuned diode input circuit.
30
Signals received through the broad channel
and amplified therein, are applied to the detector
I5 and appear as a direct current potential across
the resistor 3| to establish on the terminal 34 a
negative potential with respect to ground, and
35 variable in accordance with the signal strength,
while the modulation or audio frequency com
ponent also appears across the resistor BI between
ground and the terminal 34.
The diode detector arrangement, therefore,
40 comprises two diode rectifier devices, one in each
channel, each having a cathode connected to
chassis or ground and having a diode output re
sistor connected between ground and the low
potential terminal of the tuned input circuit for
the diode rectifier.
The terminals 25 and 34 are negative terminals
and may be considered as the output terminals
for the two rectiñer devices and for the two sig
nal channels from which may be conveyed the
audio frequency or modulation component of the
received signals.
Each of these terminals is coupled to a com
mon audio frequency amplifier comprising an
input amplifier stage having an amplifier device
3B comprising a cathode 39 connected to ground
40, a control grid 4I connected to an input lead
42, and an output anode 45 connected with an
output circuit 46 leading to the remainder of
the audio frequency amplifying system repre
60 sented by the rectangle enclosure 4l. This is
connected to an output loud speaker device indi
cated at 48.
The audio frequency output coupling to the
circuit 46 includes an output coupling reactor 0.9
65 and iilter resistor 50 provided with a by-pass ca~
pacitor 5I for supplying to the anode 45 the
operating potential as indicated from any suit
able source.
The input lead 42 for the single audio frequency
70 amplifier and the output terminals 25 and 35 are
interconnected through a resistor network com»
prising a pair of resistors 53 and 54 connected in
series between the output terminal of one diode
rectifier device and the output terminal of the
75 other diode rectifier device through output leads
indicated at 55 and 56. The lead 42 is connected
to an intermediate tap 51 between the two series
connected resistors.
Since the cathode 39 of the first audio fre
quency amplifier 38 is connected to ground and
therefore to the positive terminals of both diode
rectifier output circuits, the grid 4I is subjected
to and receives a portion of both the biasing and
modulation potentials from both signal chan
nels, and one or the other of the signal channels 10
may predominate in supplying signals depending
upon the operation of their respective automatic
volume control means I I and I2, without the in
termediary of any switching means. If both
channels are operating it will be seen that the 15
output of each diode is impressed upon the ñrst
amplifier grid 4I.
In order however to keep the inter-channel cou~
pling through the resistor output network as low
as possible the resistance of the resistor 53 should 20
be relatively large or high with respect to the
resistance of the diode output resistor 26 and
similarly the resistance of the resistor section 54
should be relatively high with respect to the re
sistance of the diode output resistor 3I. Assum 25
ing the resistances of the diode output circuits to
be R1 and the resistance of each section of the
resistor elements 53 and 54 to be R2 then the
ratio
30
B2
Ri
should be maintained as large as practically pos
sible in any receiving circuit. The limit of this
ratio is generally determined by the resistance of
the diode output circuit which may be 100,000
ohms, for example, and the resistors 53 and 54
may then have a resistance preferably of 2 meg
ohms, for example.
The circuit has the further advantage that
either channel may be cut off by simple switching
means comprising a two point switch having a
switch arm 60 and two contacts 6I and 62. The
switching arrangement is effected by connecting
the arm 60 to ground or chassis as indicated at
63, and by connecting each contact 6I and 62 to
the respective negative output terminals for the
diode circuits and in this case with the output
leads 56 and 55 respectively at the input terminals
of the resistors 53 and 54.
By connecting the arm 60 to the terminal 6I, 50
for example, it will be seen that the diode out
put resistor 3I is short-circuited and grounded
while the input end of the resistor 53 remains
connected to the terminal 25. If the resistor
sections 53 and 54 are equal as is the usual case
where aqual output is desired from both receiv
ing channels, the grid connection 42 is then ef
fectively tapped down halfway on the whole
output resistor comprising both sections 53 and
54 which is then effectively connected across 60
the output resistor 26. In this manner the audio
frequency channel receives only the signals from
the sharp channel.
In a similar manner, by connecting the arm
60 to the contact 62 the sharp channel may be
cut off and the output from the broad channel
may then be taken through the lead 42 at a
voltage tap provided by the terminal 51. The
portion of the total output voltage available is
determined, as before, by the relation between 70
the resistances of the two sections 53 and 54
which are preferably equal, although not neces
sarily so.
For example if it is desired to receive a signal
voltage from the sharp channel in a greater 75
2,127,816
proportion with respect to that from :thebroad
channel, the tap 51 may be connected electrically
more adjacent to the output terminal 25 by re
ducing Athe value of the resistor 53. This may
be done in case that the broad channel is re
sponsive to relatively strong signals and the same
output voltage is desired for both the -broad
and sharp channel without adjusting the auto
10
15
25
30:
matic volume control means for this purpose.
The operation of the system described is as
follows: With the switch Bß,-6|-62 open, sig
nals received through the sharp channel and
through the broad channel are rectified in the
separate detectors |4 and l5 and both the audio
frequency and direct current components thereof
appear between ground and theA leads..55 and 55
connected with the output terminals 25 and 34
respectively. -Since the cathode `39 is connected
to ,ground 40 and the grid 4| of theñrst audio
frequency amplifier is connected to the `tap 57|,
the audio frequency and signal voltages appear
ing in the leads 55 and 56 with respect to ground
are applied between the grid 4| and the `ca
thod 39.
This results in an `increasing signal bias for
the grid 4| as the signal strength increases and
the tube <38 may then operate without overload
ing. The combined signals are applied to the
output circuit 46 and appear at the loud speaker
48. If both signal channels are tuned to the
same carrier wave and the automatic volume
control l2 is effective to cut off the signals from
the broad channel until a predetermined higher
signal amplitude is obtained, then the sharp
35 channel alone or to a greater degree supplies
the signals to the loud speaker 43. However as
the »broad channel becomeseffective to supply
signals the .same are applied through the cou
pling network to the grid 4| without switching
40 change and without intercoupling between the
two channels, by reason of the relation of the
impedances or resistance of the output resistors
26 and 3| to the coupling resistors 53 and 54.
Any suitable arrangement may be provided for
45 controlling the two signal channels and any
suitable automatic volume control meansmay
be provided for operating the two channels in
any suitable relation to eachother, since the
mixing of the signals and the provision of biasing
potential for the audio frequency amplifier is
automatically obtained without switching con
nections. It should be understood that the
switch 6B is provided merely for cutting ofi` one
or the other of the channels as may be desired,
and does not interfere with normal operation
when open.
With this arrangement, for example, the two
channels may be turned to separate signals, such
as a broadcast program on the broad channel, for
example, and with a sharp channel tuned to
police or S. O. S. signals which will be applied
automatically to the loud speaker 48 when re
ceived, without further attention from the listen
er. Also, the switch 6U may be operated to
651 listen selectively to either channel.
This provides a desirable arrangement in po
lice or aircraft receivers, for example, where the
two channels are tuned to differing transmitting
stations and both may be heard »or either one may
be selected by the simple switching means in the
audio frequency mixing circuit. In this case,
a noise suppresserin each channel is desirable,
to cut ofi either of the channels when not re~
ceiving a carrier wave.
d
In certain applications it may be desirable to
3
connect the receiving channels with a high gain
audio frequency amplifier tube, as shown in Fig
ure 2, to which attention is now directed and
in which the same reference numerals are used
for like parts as in Figure 1.
Referring to Figure 2, a. high gain audio fre
quency amplifier tube 65 of the `pentode type, is
provided with a control grid 66 connected with
a movable contact 61 of a volume control potenti
ometer 68. The grid circuit is completed through
the potentiometer 68 and a ground or chassis
connection 69, and biasing potential is derived
from a self-bias resistor 10, as shown. The out
put anode of the amplifier, indicated at 1|, is
connected to a suitable output circuit 12 through
a coupling capacitor 13, in conjunction with a
coupling resistor 14 in the anode circuit. Posi
tive B potential for the anode is supplied to the
coupling resistor 14 through a filter resistor vl5,
as indicated.
The input grid circuit, comprising the resistor
elementßß, is coupled to the output lead 42 from
the output terminal 51, between the output resis
tors 53 and 451|, through a coupling capacitor 81
which serves to transfer the audio frequency sig
nal to the amplifier grid circuit while isolating 25:
the two circuits against .direct current potential.
With this arrangement, the amplifier tube 65
may be self-biased lor biased in any suitable man
ner yindependently of the signal potential, and the
potentiometer E'l-GB serves to providev volume
control means directly for the audio frequency
circuit, following the signal combining network
in connection with the two detectors.
By this means, the signal volume may be ad
justed to `any desired level for both channels
jointly. With the signal channels controlled by
suitable automatic volume control and noise sup
pression means, the volume control device 61--68,
following the channel mixing network, may pro
vide the only volume control means for the receiv
ing system.
While the invention has been described in con.
nection With‘a superheterodyne- receiving system,
it is `apparent that it may be applied to any re
ceiving system having two signal receiving chan
nels suitably controlledby automatic volume con
trol and/or noise suppression means, with the
channels terminating in suitable diode rectifier
devices and followed `by a single audio frequency
amplifier channel.
We claim -as our invention:
1. In a multiple signal .channel radio receiving
system, the combination of» a pair of diode signal
rectifier devices each having a cathode, a rectified
signal output terminal and an output impedance
connected vbetween said cathode 4and said termi
nal, a pair of direct current conducting output
impedance elements connected in series between
said terminals, an audio frequency amplifier >de
vice having a cathode and having a control grid
conductively connected between said impedance
elements, and means interconnecting the `cathodes
of said rectifier devices and the cathode of said
amplifier device, whereby signals applied to said
rectifier devices are rectified and jointly applied
with the direct current component thereof to said
control grid.
,
2. In a multiple signal channel radioxreceiving
system, the combination of a pair of vdiode sig-,nal 70
rectifier devices each having a cathode and `a
rectified signal output terminal, a pair of output
resistance'elements connected in series between
said terminals, an audio frequency ampliiier'lde
vice having a .cathode `and having a control grid
4
2,127,816
connected between said resistance elements, and
means interconnecting the cathodes of said recti
fier devices and the cathode of said amplifier de
vice, whereby signals applied to said rectifier de
vices are jointly applied to said control grid there
from, said resistance elements having a relatively
high resistance each with respect to the rectifier
output circuits, whereby said signal channels are
effectively decoupled while being interconnected
10 with said control grid.
3. In a radio receiving system having a pair of
signal receiving and amplifying channels, the
combination of a pair of diode rectifier devices,
one coupled to each of said channels to receive
15 and to demodulate the signal output therefrom,
automatic volume control means for each of said
channels effective to control the amplitude of
signals applied to said diode rectifier devices,
each of said diode rectifier devices comprising a
cathode connected to ground and having a diode
output resistor connected at its positive termi
nal to said cathode and ground, a pair of signal
and biasing potential output leads, one from a
negative terminal of each of said output resistors,
a pair of series connected resistor elements each
having a relatively high resistance with respect
to each of said diode output resistors connected
between said output leads, and a common audio
frequency amplifier for said channels having an
input amplifier tube provided with a cathode con
nected to ground and a control grid connected to
an intermediate tap point between said series
connected resistor elements whereby the signal
output and bias potential from said signal chan
nels are applied jointly to said amplifier device,
4. In a radio receiving system having a pair of
signal receiving and amplifying channels, the
combination of a pair of diode rectifier devices
one coupled to each of said channels to receive
and to demodulate the signal output therefrom,
automatic volume control means for each of said
channels effective to control the amplitude of
signals applied to said diode rectifier devices, each
of said diode rectifier devices comprising a
cathode connected to ground and having a diode
output resistor connected at its positive terminal
to said cathode and ground, a pair of signal and
biasing potential output leads one from a nega
tive terminal of each of said output resistors, a
pair of series connected resistor elements each
having a relatively high resistance with respect
to each of said diode output resistors connected
between said output leads, a common audio fre
quency amplifier for said channels having an in
put amplifier tube provided with a cathode con
nected to ground and a control grid connected to
an intermediate tap point between said series
connected resistor elements whereby the signal
output and bias potential from said signal chan
nels are applied jointly to said amplifier device,
and means for selectively grounding either of said
output leads thereby to render ineffective either
of said signal amplifying channels selectively.
5. In a radio receiving system, the combina
tion with means providing two signal amplifying
channels therein, of means for combining the
signal output from said channels comprising an
audio frequency amplifier, a diode rectifier de
vice connected with the signal output end of each
70 of said channels, a diode rectifier output resistor
in circuit with each of said diode rectifier de»
vices, a resistor network connecting said diode
output resistors substantially in parallel relation
to each other, and a circuit connecting said am
75 pliñer with said network whereby said amplifier
may receive biasing potential from each of said
channels and signal potentials jointly substan
tially in parallel.
6. In a radio receiving system, the combination
with means providing two signal amplifying
channels therein, of means for combining the sig~
nal output from said channels, comprising an
audio frequency amplifier, a diode rectifier device
connected with the signal output end of each of
said channels, a diode rectifier output resistor 10
in circuit with each of said diode rectifier de
vices, a resistor network connecting said diode
output resistors substantially in parallel relation
to each other, and a circuit connecting said am
plifier with said network whereby said amplifier
may receive biasing potential from each of said
channels and signal potentials jointly, substan
tially in parallel, said resistor network providing
a relatively high resistance between said chan
nels whereby they are substantially decoupled 20
while being maintained in parallel connected re
lation to each other in connection with the am
plifier.
7. In a radio receiving system, the combination
with means providing two signal amplifying 25
channels therein, of means for combining the
signal output from said channels, comprising an
audio frequency amplifier, a diode rectifier de
vice connected with the signal output end oi
each of said channels, a diode rectifier output re
sistor in circuit with each of said diode rectifier
devices, a resistor network connecting said diode
output resistors substantially in parallel relation
to each other, a circuit connecting said amplifier
with said network whereby said amplifier may
receive signal potentials jointly from said rec
tifiers, Substantially in parallel, and means in
connection with said resistor network providing
a single variable volume control element inter
posed in circuit between said amplifier and a
potential supply point on said network.
8. In a radio receiving system, the combination
with means providing two signal amplifying
channels therein, of means for combining the
signal output from said channels, comprising an
audio frequency amplifier having an amplifier
tube, a diode rectifier device connected with the
signal output end of each of said channels, a
diode rectifier output resistor in circuit with each
of said diode rectifier devices, a resistor network
connecting said diode output resistors in parallel
relation to each other through the negative ter
minals thereof, a circuit connecting said ampli
fier tube with a potential supply terminal of said
30
35
40
45
50
network, to receive signal potentials through said 55
network from each of said channels jointly, sub
stantially in parallel, said resistor network pro
viding a relatively high resistance between said
channels whereby they are substantially decou
pled while being maintained in parallel connected 60
relation to each other in connection with the am
plifier tube, said amplifier tube being of the high
mu type, impedance coupling means including
a coupling capacitor between said tube and said
resistor network, and means for applying a bias 65
ing potential to said amplifier tube.
9. In a radio signal receiving system having a
pair of signal amplifying channels, the combina
tion of a diode rectifier device in each channel
having a cathode and a rectifier output resistor
connected to ground with the cathode, a pair of
resistors connected in series between the diode
output resistors, switch means for selectively con
necting either of the outer terminals of said
series connected resistors to ground, and an audio
5
2,127,816
frequency amplifier having a cathode connected
to ground and a control grid connected with a
point along said series connected resistors to re
11. In a radio signal receiving system having
a pair of signal amplifying channels, the combi
ceive rectified signals jointly from said amplify
ing channels.
10. In a radio signal receiving system having
a pair of signal amplifying channels, the combi
nation of a diode rectifier device in each channel
having a cathode and a rectifier output resistor
connected to ground with the cathode, a pair of
resistors connected in series between the anode
ends of the diode output resistors, switch means
nation of a diode rectifier device in each channel
having a cathode and a rectifier output resistor
connected to ground with the cathode, a pair of
for selectively connecting either of the outer ter
minals of said series connected resistors to
ground, and an audio frequency ampliñer having
resistors connected in series between the anode
ends of the diode output resistors, switch means
for selectively connecting either of the outer ter
minals of said series connected resistors to
ground, and an audio frequency amplifier having
a cathode connected to ground and a control grid
connected with a point along said series con
a cathode connected to ground and a control grid
conductively connected with a point along said
series connected resistors to receive rectified sig
nals and biasing potential jointly from said arn
plifying channels.
nected resistors to receive rectified signals joint
ly from said amplifying channels, said last named
connection including a Volume control poten
tiometer device for jointly controlling the signal
output from both amplifying channels.
POUL F. G. HOLST.
LOREN R. KIRKWOOD.
20
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