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Jan. 14, 1947.’
w. LYONS
mxvmnsw? RECEIVINGHSYSTEM
12,414,111 ’
mined March.22, 1944 -
+3
+3
+5
+5
+5
INVENI'OR
ONS
WALTER
B‘’ >‘ Z
"
fur-“0v
ATTORNEY '
Patented Jan. 14, 1947
2,414,111
UNITED STATES PATENT OFFICE
‘
2,414,111
DIVERSITY RECEIVING SYSTEM
Walter Lyons, Wenonah, N. J ., assignor to Radio
Corporation of America, a corporation of Dela
ware
Application March 22, 1944, Serial No. 527,572
11' Claims. (Cl. 250-20)
2
This invention relates to diversity receiving
systems and more particularly to that type of
radio receiving equipment which makes provision
for combining the signal energy derived from di-f
ferent antennae and separately ampli?ed in dif
ferent radio receiving circuits.
drawing, the sole ?gure of which represents dia
grammatically a preferred circuit arrangement
for carrying out the invention.
Referring to the drawing, I show illustratively
two receiving antennas l ‘and 2 which are indi
vidually connected to radio frequency ampli?ers
It is common practice to provide a plurality
3 and 4. The output from each of these ampli
?ers is fed to an appropriate converter 5 and 6.
A local oscillator 1 provides energy of a suitable
of heterodyne receivers each connected to an in
dividual receiving antenna, the several antennae
being spaced apart so as to minimize the effects 10
frequency for heterodyning with the ampli?ed
of fading. In some of the well-known diversity
signals in each of the converters 5 and 6, thus
receiving systems, means are provided for auto~
producing a heterodyne frequency which is then
matically switching the signals through alterna
tive ampli?ers so as to maintain connection of
a responsive device to the particular ampli?er
which at any moment is receptive of the strongest
signals.
In another group of developments in diversity
.11
fed to the intermediate frequency ampli?ers.
One of these IF ampli?ers includes the discharge
tubes 1 l, 13, and 15. Another of these IF am
pli?ers includes the discharge tubes l2, l4, and 16.
Each of the tubes H to l G inclusive is shown as a
pentode, although other types of ampli?er tubes
receiving systems the practice is adopted of feed
may be employed, if desired.
ing recti?ed output potentials from the inter 20
The control grid in the ?rst stage tube 11 of
mediate frequency ampli?ers to a common load
the one IF‘ ampli?er is connected to a common
which is permanently coupled to each of these
automatic gain control circuit I‘! through the
intermediate frequency ampli?ers operating in
secondary
winding of a coupling transformer l8.
parallel and contributing to the output one at a
This secondary winding is tuned by connecting
time where the inputs are unequal by a substan
an adjustable condenser 8 across its terminals.
tial amount, or both supplying output where the
Likewise in the second IF ampli?er the control
inputs are substantially equal. My invention be
grid of tube 12 in the ?rst stage is connected to
longs in this group. I have found that reception
the common AVC circuit 11 through the second
can be greatly improved when the gain of each
ampli?er is automatically adjusted so that the 30 ary winding of a coupling transformer 20. This
secondary winding is also tuned by means of an
individual ampli?ers shall be capable of con
adjustable condenser 8.
tributing substantially equally to the common
In the second stage of each IF ampli?er tubes
load regardless of the working strength of the
13 and 14 are shown with their control grids con
incoming signals applied to each ampli?er. Thus
nected similarly to the input circuit connections
the working signal may be 10 microvolts or 1,000
of the ?rst stage. That is to say, each of these
microvolts intensity and all ampli?ers will be
second stage tubes is rendered subject to the com
capable of contributing equally to the common
mon AVC potentials. The second stage input
load for equal signal input at the antennas. This
circuits are also fed with signal energy by virtue
improvement is particularly needed in cases
of inductive coupling to the output circuit in the
where a common automatic gain control circuit
?rst stage, as is conventional. The interstage
is provided for the individual ampli?ers and
couplings are shown in the one IF ampli?er to
where the potentials utilized in the AVG circuit
include transformer 22 both primary and sec
are derived from the average signal strength of
ondary windings of which are tuned to the IF
all of the individual diversity receivers.
frequency‘; and in the case of the second 1F am
It is an object of my invention to provide means
pli?er, transformer 23 is used. In fact the said
for automatically adjusting the gain in’ each of
connections for the two IF ampli?ers are iden
a plurality of receivers connected in a diversity
tical in arrangement. A tuning condenser 8 is
system so as to compensate for variations in the
connected in shunt with the primary and with
relative input signal‘levels of the individual re
the
secondary of each interstage coupling trans
ceivers and so that the output signal energy 50 former.
derived from each ampli?er shall be of substan
The screen grids in the ?rst two stages of both
tially equal magnitude.
IF
ampli?ers are connected through series re
Other objects and advantages of my invention
sistors 24 and 25 respectively to the positive ter
will be made apparent in the detailed description
minal of the direct current operating source in
to follow. This description is accompanied by a
dicated as +B. Resistor 24 in series with an
2,414,111
adjustable resistor 26 constitute a voltage divider
whereby the normal voltage to be applied to the
screen grids of tubes I I and I3 is obtained. Like
wise resistor 25 in series with the adjustable re
sistor 21 constitute a similar voltage divider for
obtaining the normal screen grid potentials to
be applied in tubes i2 and i4. These screen grid
potentials, however, are made automatically ad
justable by means of two discharge tubes 28 and
29, the space paths of which are disposed in shunt
with the adjustable resistors 26 and 21 respective
ly. Capacitors 9 are used to bypass to ground the
alternating potentials which appear on any of
4
space paths 0 and a through resistors M of rela
tively high impedance. Resistors 44 in combina
tion with capacitors 55 provide time constant
circuits which are relatively long. They may be
adjusted, for example, to produce a delay action
of as much as 10 seconds or more in the control
of the tubes 28 and 29. The reason for intro
ducing a considerable delay period into the com
pensating adjustment of the screen grid poten
tials as between the two receivers is that this
action must be maintained distinct from that of
the conventional AVC circuit, especially where
the control potentials of the latter are to be ap
plied in common to both receivers in dependence
the screen grids.
upon the recti?ed output from the receiver de
15
Each of the tubes 28 and Z9 is preferably of
livering the strongest signals.
the triode type and their control grids are sub
For the relatively slow adjustment of the gain
jected to variable control biases, each in depend
in each receiver in dependence upon the ?oating
ence upon the recti?ed signal output level of a
average of signal output intensity from the other
different amplifier. This will be explained fur
receiver, assume ?rst that antenna 2 is deliver
ther after describing the circuit connections of 20 ing
signals of dominating intensity. Then the
the third stage in each of the IF ampli?ers.
impedance
of the space path in tube 23 is eventu
The control grid in tube l5, which is in the
ally
increased
in proportion to the intensity of
third stage of one IF ampli?er, is coupled to the
the recti?ed signal potentials derived from tube
output circuit of tube l3 across transformer 33.
Likewise the control grid in tube [6, which is in 25 It and recti?ed in space path c of the twin diode
tube 3 l . The effect of this increase of space path
the third stage of the second IF ampli?er, is
impedance in tube 28 is to increase the screen
coupled to the output circuit of tube M across
grid potentials, and hence the gain, in tubes H
transformer 3|. Each of the tubes I5 and I6 is
and I3. Assume now that antenna i. delivers
provided with a cathode resistor 32. These cath
ode resistors ‘are shunted by capacitors 33 as is 30 the stronger signals. Then the gain in ampli?er
tubes l2 and I4 is increased by raising the screen
usual. The screen grids in tubes l5 and it are
grid potentials of these tubes in'response to a
connected to the +13 terminal through series
resulting increase in the space path impedance
resistors 34. The only gain control action in
of tube 29, where the signal output potential is
tubes l5 and I6 is, therefore, that which results
from the self-biasing effects of the cathode re 35 derived from tube 15 and recti?ed in section a
of the detector tube 40.
sistors 32.
,
Recti?cation of the IF ampli?er output for
The output circuit of tube l5 includes a reso
application to a utilization device, or audio fre
nant circuit 35, the inductance of which consti
quency responsive unit, is accomplished vby means
tutes the primary winding ‘of an output trans
of the space paths b and d in the diode tubes
former 36. Likewise, the output circuit of-tube
40 and ill respectively. These space paths are
i6 includes the resonant circuit 31, the induct
ance of which constitutes the primary winding
in circuit with the common load 39. Path 11 is
in output transformer 38. The secondary wind
in series with the secondary of transformer 36.
ings of transformers 36 and 38 are both connected
Path d is in series with the secondary of trans
to a common load 39. The terminal of the load 45 former 38.
impedance 39 remote from the transformer wind
ings is grounded. This load impedance may,
therefore, be used to supply output potentials for
feeding, the signals to any suitable utilization
The two secondaries are tuned by
parallel capacitances 8.
The common load 39 is preferably shunted by a
capacitor 4'! for peak detection and ?ltering. Ca
pacitor
49 serves to isolate the utilization device
device. The output terminals are indicated at 48. 50 from D. C. components in the load 39. Its use is
In order that each of the IF ampli?ers may
optional. The output leads are indicated at 48.
have its gain somewhat slowly adjusted in ac
The automatic gain control circuit I? is con
cordance with the ?oating average of amplitudes
nected through a resistor 50 to the common load
of the signal output from the other ampli?er,
39, as is conventional. A capacitor 5i operates in
I have made the grid in tube 28 subject to the
conjunction with resistor 50 for obtaining the de
delayed in?uence of recti?ed output potentials
sired time constant in the operation of the AVG
from tube 16. correspondingly, the grid in tube
circuit. Resistors l9 carry the AVG potentials
29 is made subject to the delayed in?uence of
to the grids in the RF ampli?ers 3 and 4, and
recti?ed output potentials derived from tube l5.
in the tube stages H and i2. Bypass condensers
Recti?cation in the one case is obtained in the 60
iii are also used conventionally in association with
space path 0 within the twin diode tube 4|, which
resistors
I!) for draining o? to ground any A. C.
develops a D. C. potential drop, negative with
potentials
which may appear in the AVG circuit.
respect to ground, in a resistor 520. This recti?er
It Will be apparent that the retarded compen
circuit is coupled to the output circuit of tube
it; through capacitor 43. Recti?cation in the 65 sation of gain in the two receivers may be accom
plished independently of the conventional AVC
other case is obtained in the space path a within
control if di?erent stages of ampli?cation are
the twin diode tube 40. The D. C. potential so
rendered subject to one and to the other of the
developed in resistor 52a results from coupling
two types of gain control. In this suggested mod
this recti?er circuit to the output circuit of tube
it is unnecessary to apply the compen
l5 through capacitor 42. Resistors 52a and 52c. 70 i?cation
sated gain regulation through the screen grids.
are each shunted by a capacitor 53 for draining
as has been described in the foregoing illustrative
off to ground any existing high frequency com
embodiment. Instead, the tubes 28 and 29 may
ponents.
be used to apply a more positive (or less nega-'
The grids in tube 28 and 29 are connected re
spectively to the detector circuits of the diode 75 tive) bias to the control grid in one or more stages
2,414,111
of one receiver in response to an increase in the
output intensity of the other receiver.
'
My invention is, of course, capable of modi?
cation in various other ways, as will be under
stood by those skilled in the art, in order to meet
diiferent requirements. The circuit shown and
described is merely illustrative, although I have
found it to be practical.
In fact it appears to
possess many advantages over diversity receiving
systems heretofore known.
I claim:
‘
1. In a diversity receiving system having two
receivers each individually fed with signal en
ergy which is collected by a separate antenna,
each receiver being characterized by the inclusion
of a plurality of ampli?er stages having screen
grid tubes, apparatus for equalizing the signal in
tensities delivered as recti?ed output from the re
spective receivers and applied to a common utili
6
' 4'. In a diversity receiving’system having a plu~
rality of receivers‘separately fed with signal en
ergy collected by antennae which are spaced
apart, a plurality of ampli?er stages in each of
said receivers, a multigrid discharge tube in each
stage, a direct current operating potential source
connected to the tube electrodes, a voltage dié
vider individual to each receiver and connected
across terminals of said source, a, controllable dis~
10 charge device in shunt with a portion of each said
voltage divider, a gain control circuit for each
receiver, comprising connections from a point on
its respective voltage divider to at least one of
the'screen grids in its ampli?er tubes, and means
recipro'callyoperable as between the gain control
circuits of the diiferent receivers whereby an am~
plitude increase in the output of recti?ed poten
tials delivered by one receiver serves to control
the
discharge device which is in shunt with the
zation device, said apparatus comprising a direct 20
voltage divider portion appropriate to a differ
current source of screen grid potential shunted
ent receiver, wherein the gain is thus increased.
by potentiometers. which are individual to each
5. In a diversity receiving system having two
receiver, two electronic circuit impedances each
receivers
and a ‘separate antenna feeding signal
in shunt with a respective section of said poten
energy to each receiver, a load common to cer
tiometers, said sections being‘connected to the
tain output components derived from the two
negative terminal of said source, means for recti
receivers,
means for separately rectifying other
fying an output component from each receiver,
output;
components
from each receiver, a multi
and means for utilizing each said output com
grid discharge tube in each ampli?er stage of
ponent from a respective receiver to vary the said
electronic circuit impedance appropriate to the 30 said receivers, a direct current source for acti
vating said tubes, two voltage dividers connected
other receiver.
across
the terminals of said source, each of said
2. In a diversity receiving system having two
dividers having a tap thereon for feeding screen
receivers separately fed with signal energy col
grid potentials to certain of said multigrid tubes
lected by antennae which are spaced apart, each
in
the respective receivers, and electronic means
receiver being characterized by the inclusion of 35 operably
associated with said voltage dividers and
a plurality of ampli?er stages having screen grid
subject to control by said rectifying means in
tubes, apparatus which compensates for inequali
such manner as to cause said screen grid po
ties of receptive conditions at the two antennae
tentials as applied to the screen grids in one
comprising means for separately rectifying the
receiver to be varied as a direct function of
output from each receiver, electronically con 40 the amplitude of the recti?ed signal component
trolled potentiometric means for varying the
separately derived from the other receiver.
screen grid potentials in, and hence the sensitiv
6. The combination according to claim 5 and
ity of, each receiver in dependence upon the am
including an automatic gain control circuit com
plitude of the recti?ed output from the other re
mon to both receivers, said circuit being respon
ceiver, means for rectifying a component of said 45 sive to potential variations in said common load.
output from the receiver which delivers the
7. In a diversity receiving system comprising
strongest signals and for utilizing the same as a
two
receivers A and B, each receiver having its
common gain control potential, and means for
input circuit coupled to a separate antenna and
applying said common gain control potential to
having a multistage ampli?er, a multigrid dis
certain ampli?er stages in both receivers.
50 charge tube in each ampli?er stage, a direct cur
3. A diversity receiving system comprising two
rent source having suitable connections to the
receivers each fed with signal energy by its own
electrodes of said tubes for activating the same,
antenna, at least one ampli?er stage in each re
means for rectifying and combining in a common
ceiver having a screen grid tube arranged for reg
load impedance certain output component-s de
ulating its ampli?cation ratio by" control of the 55 rived from the two receivers, further means for
screen grid potential applied thereto, a direct cur
rectifying and segregating other output com
rent source for energizing the discharge tubes in
ponents from each individual receiver, a pair of
said ampli?er stages, two voltage dividers con
triode discharge tubes each separately controlled
nected across the terminals of said source, con
:by one and the other, respectively, of said segre
nections from an intermediate point on one of 60 gated output components, and means individual
said voltage dividers to the screen grid of said
to each receiver for applying variable screen grid
screen grid tube of at least one ampli?er stage in
potentials to certain of its ampli?er discharge
one of said receivers, similar connections from a
tubes, the last said means being effective through
corresponding point on the other voltage divider
said triode discharge tubes to control the gain
to the screen grid of said screen grid tube of at 65 in receiver A in dependence upon the amplitude
least one ampli?er stage in the other receiver, and
of recti?ed signal output derived from receiver
two discharge devices having their space paths
B, and vice versa.
connected each in shunt with a portion .Of one of
8. A diversity receiving system in accordance
said voltage dividers respectively, each of said dis
with
claim 7 and including an automatic gain
charge devices having a grid for controlling the 70 control
circuit operative in dependence upon the
impedance of its space path, and the grid of the
amplitude of the output components which are
discharge device which serves to regulate the
combined in said common load, said gain con
screen grid potentials in one receiver being con
trol circuit being connected to the control grids
trolled by output potentials derived from the other
in certain of the ampli?er stages of both re
receiver, respectively.
75 ceivers.
2,414, 1 1 1
7
9. A diversity receiving system in ‘accordance
8
of the order of ten seconds or more in the singu
lar control of each of said pair of discharge
tubes, whereby a retarded equalization of the
output from the two receivers is obtained.
11. In a diversity receiving system comprising
two receivers each fed with signal energy by
its own antenna, each receiver having output
with claim 7 and including in each of the stated
means for applying variable screen grid poten
tials a pair of voltage dividers each individual
to the screen grid potential supply circuits of
the separate receivers, a portion of each voltage
divider being shunted by the space path of a
connections to a common load and further out
respective one of said triode discharge tubes.
put connections to each of two gain control sys
10. A diversity receiving system comprising two
tems one of which is effective for adjusting the
receivers each fed with signal energy by its own 10 gain in both receivers in dependence upon the
antenna, a plurality of ampli?er stages in each
predominating output from either receiver, and
receiver, certain of said ampli?er stages having
the other gain control system constituting means
input circuits which include a common control
for causing the gain in each receiver to be varied
grid biasing source, recti?er means individually
as a direct function of the output from the other
coupled to the output circuit of the ?nal stage
receiver, a circuit organization for operating said
in each receiver for detecting the audio frequency
gain control systems which comprises means for
components of the received signals, a common
rectifying an output component from each re
load for said components, a gain control circuit
ceiver, means for utilizing said recti?ed output
responsive to potential variations across said
common load for influencing the effective value 20 for purposes of common gain control in both re
ceivers, means for separately rectifying another
of said grid biasing source, other recti?er means
output
component from each receiver to be ap
individually coupled to the output circuit of the
plied as a gain control potential in the other
?nal stage in each receiver, a pair of discharge
receiver, and means for introducing consider
tubes each having an input circuit subject to
ably more delay in the application of the last
25
control by recti?ed output from said other rec
said gain control potentials than in the common
ti?er means associated with a respective receiver,
gain control potentials.
and having an output circuit eifective to in
WALTER LYONS.
?uence the gain in a different receiver, and two
time constant circuits each having a delay period
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