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Патент USA US2151081

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Mafch 21, 1939.
Filed Sept. v2.4, 1936
2 Sheets-Sheet 1
Patented Mar. 21, 1939
Wendell I). Carlson and Vernon D. Landon, Had
don?eld, N. 5., assignors to Radio Corporation
of America, a corporation of Delaware
Application September 24, 1936, Serial No. 102,286
2 Claims.
Our invention relates to a multiplex radio re
ceiving system. More particularly our invention
includes in combination ‘a plurality of antennas,
band ampli?ers, and distributing system for mul
5 tiplex radio reception.
‘We are aware of systems in which a plurality
of‘ radio receivers are connected to a common
antenna. Such systems are often character
ized by mutual reactions when the several re
“) ceivers are tuned, or cross talk if coupling tubes
are connected between the several receivers and
the common antenna. We are further aware
that a common antenna has been used with a
broadly tuned ampli?er whose'output circuit in
15 cludes the input to a plurality of radio receivers.
This arrangement requires a high-gain ampli
?er which has a uniform ampli?cation charac
teristic over a very broad band of frequencies, if
the system is to be used with a plurality of all
20 wave receivers. An ampli?er of high gain and
uniform ampli?cation is usually subject to cross
talk, interference, and hiss when directly cou
pled to an antenna and to further di?iculties
due to the resonant characteristic of the antenna.
We propose to overcome these dii?culties by
connecting a plurality of antennas, each re
sppnsive to radio signals covering a band of fre
quencies, to a plurality of radio frequency am
pli?ers, each substantially uniformly responsive
30 to" currents impressed on it by its associated
tubes within their rated capacity to lessen cross
modulation; and to attenuate harmonic output
currents by employing narrow band output
In the accompanying drawings Fig. 1 is a
schematic circuit diagram of one embodiment
of our invention,
Fig. 2 is a graph showing the frequency char
acteristics of the radio frequency coupling trans
formers, and
Fig. 3 is a schematic illustration of one ar
rangement of a plurality of antennas.
While the foregoing objects are the prime de
sideratum, the number of channels formed by
separate antennas and separate band ampli?ers 15
can be increased to an impractical extent. By
way of example, we have found the following
channels and channel widths, satisfactory for re
ceiving signals whose frequency is between 2
megacycles and 18.1 megacycles.
First channel 3-4.6 m. 0.
Second channel 4.6-7.3 m. 0.
Third channel 73-10 m. 0.
Fourth channel 10-12.7 m. 0.
Fifth channel 12.7-15.4 111. c.
Sixth channel 15.4-18.1 m. 0.
~ In the present broadcast frequency band we
have employed a single antenna and three am
pli?ers to cover the following ranges:
antenna. Suitable resonant networks, connected
between the antennas and the ampli?ers, may be
used to attenuate interfering signals which might
Ampli?er 1 ___________ __
Ampli?er 2 ___________ __
otherwise cause cross talk or block the ampli
Our invention may be best understood by ref
erence to the accompanying circuit diagram Fig. 5
1, which schematically illustrates one embodi
ment. Referring to the circuit diagram, an an
tenna l is coupled through a suitable transmis
sion line 3 to a transformer 5. The primary
of the transformer 5 is a tuned circuit, which is 40
One of the, objects of our invention is to pro
vide means whereby a plurality of all wave re
ceivers may be operated from common antennas
and amplifying systems.
(Cl. 250-9)
Another object is to provide a plurality of an
tennas, each responsive to currents of a band of
radio frequencies, and means coupling the an
tennas to band responsive ampli?ers whose out
put circuits have a common connection to a plu
45 rality of all wave receivers.
A further object is to provide means for at
tenuating interfering signals which tend , to
block the ampli?ers which couple a plurality of
receiving antennas and a plurality of all wave
m 0 radio receivers.
Additional objects are: to obtain highgain from
the antenna to the input of the ?rst ampli?er to
reduce ampli?er hiss; to limit cross talk or in
terference to a narrow band by the use of a plu
i5 ,rality of band ampli?ers; to keep the ampli?er
530 to 900 kilocycles 30
900 to 1250 kilocycles
Ampli?er 3__.___________ 1250 to 1600 kilocycles
comprised of a capacitor '1 and an inductor 9.
Within the inductor winding 'is an adjustable
magnetite core II. The inductor 9 is mutually
coupled to a second inductor 13, which also in
cludes an adjustable magnetite core 15.
The 45
second inductor I3 is connected to the grid cir
cuit of an ampli?er 17, which may be any suit
able thermionic tube or the like.
The anode circuit of the ampli?er tube 11 in
cludes a transformer !9.' This transformer is 50
comprised of a pair of mutually coupled induc
tors 2|, 23, which preferably include adjustable
magnetite cores 25, 21. The primary inductor 2|
is shunted by a resistor 29. The secondary in
ductor 23 is connected to the grid circuit of an 55
ampli?er 3| which may be of any suitable type.
The output of the ampli?er 3| includes a trans
former 33. This transformer 33 is also composed
of a primary inductor 35 and a mutually cou
cults of the all-wave receivers are each connected
to a separate one of these resistors I I1. One such
connection is represented by theblock H9. In
the arrangement illustrated provision has been
pled secondary inductor 31. These inductors 35,
31, may preferably include adjustable magnetite
cores 39, til .
The secondary circuit of the trans
former 33 is completed by a capacitor 43 and a
shielded line 45, which is connected to the. sec
10 ondary circuit at an appropriate point.
shielded line is connected to a distribution net
work which will be described below.
Inasmuch as the second (4.6-7.3 m. c.) and
third (7.3-10 m. c.) channels are composed of
apparatus and circuits which differ from the
?rst channel (2-4.6 m. 0.) only in the range of
frequency response, no useful purpose would be
served by repeating the foregoing description. It
will be observed that the shielded line 45 is con
nected to the output circuits of each ampli?er.
Additional channels (IO-12.7 m.rc.'; 12.7-15.4 m.
c.; 15.4-18.1 m. 0.; etc.) , not shown, may be simi
larly included in the system.
Having described the antennas and ampli?ers
25 for the high frequency channels, the broadcast
channel will be considered. In the broadcast
band, 530 to 1600 kilocycles, a single antenna 41
is connected through a transformer 49 to a trans
mission line 5| which terminates in several res
3.0: onant circuits. A plurality of attenuatingrnet
works 53 may be connected in the transmission
line to reduce cross talk and interference caused
by signal currents of high amplitude. Each pri
mary inductor 55 is mutually coupled to a reso
35.1 nant secondary circuit which includes an induc
tor 51 and a capacitor 59. Adjustable magnetite
cores 6| are incorporated in the primary induc
tors 55.
The transmission line 5| terminates in a plu
401 rality of resonant circuits 53, 55, 6'1, which are
connected in shunt.
The inductors '69, 1|, 13,
' of these circuits are preferably tuned by mag
netite cores 15, ‘ll, 19.. These inductors 69, ‘H,
13, are mutually coupled to secondary inductors
8|, 83, 85, which. include adjustable magnetite
cores 81, 89, 9|. The secondary inductors 8|, 83,
85areconnected to thermionic ampli?ers 93, 95,
The output circuit of these ampli?ers in.
cludes resonant transformers 99, IM, Hi3, which
are composed of primary inductors including
magnetite cores and resonant secondary circuits.
These secondary circuits I05, I01‘, I09 are each
comprised of capacitors and inductors which
preferably have adjustable magnetite cores. The
secondary circuits Hi5, I01, m9 are connected to
the'shielded output lead 45.
The combined outputs from the several sep
arate channels may cover a very broad frequency
band; forexample, 2 megacycles to 181.1 mega.
60 cycles and 530 kilocycles to 1600 kilocycles. Pre
made for sixty-four receivers.v It should be un
derstood that this distribution network may be
multiplied to serve any required number of re
ceivers. Our invention is not limited to this pre
cis'e distribution network as other arrangements
may be employed.
In the' foregoing description no mention has
been made of the characteristics of the radio
frequency transformers 5, I9, 33, which couple
the antennas to the ampli?ers H, the ampli?ers’
l1, 3| to each other, and the output of the ampli 15
?ers 3| to the distribution line 45. Each trans
former consists of two tuned coupled circuits ad
justed to give a slightly double peaked response
of the proper band width. In each transformer
one of the tuned circuits is made as low loss as 20
possible. The selectivity factor of the other tuned
circuit is adjusted to the proper value for’ the‘
given band width. With the input and output,
transformers the damping is supplied bythe surge
impedance of the line which acts as a. resistance 25
in series with the tuned circuit. The band width
of such a series circuit is a function of L/R
(L=inductance, R=resistance).
Since R is the
same for each channel, L is also the same; The
inductance of the coil in series with the trans 30
mission line is the same in all short-wave input
transformers.‘ The resonantrfrequency is varied
by changing the series capacity.
In the interstage transformérsthe damping is
supplied by a shunt resistor on the primary. . 35:
With a shunt resistor the band width is a func
tion of RC (C=capacity). Since C is constant,
R is the same in each channel to give the same
band width. In each channel there are four
tuned circuits associated‘with either the plate or.
grid of a vacuum tube. In each of these circuits
the tube capacity is the chief capacity of the cir-. '
cuit, all other capacities being kept to- a mini-'
mum. This: is the condition for amaximum prod‘-. '
uct of gain times band width.
All of the'resonant circuits of‘ each channel are
tuned to the proper frequency by‘ the adjustable‘
magnetite cores. An exception‘is'the 24.6mm.
channel, where the tight coupling'requiredmakes' '
it impossible to separately tune’ the‘two resonant 50
circuits of each transformer.
used in this band.
Fixed tuning - is
The inputtransformers haverra gain of about
?ve from the transmission line to the ?rst'grid;
The interstage transformers have a gainof about. 55
8 from grid to grid.
The output transformers
have a gain of about unity from'grid to line." The‘
overall gain from line to line is about 40. Figure
2 gives a performance curve'A on a typical‘input '
transformer. Curve-B represents an interstage 60
transformer. A graph C shows the corresponding
output transformer and the overall curve for the
cautions must be observed in the design of a dis
tribution network to cover such frequency range.
f i
In such network we have found a bi?lar-wound, channel is designated as D.
step-down transformer with a two to- one ratio
satisfactory. In the preferred arrangement one nected to- the same load, they may be'designed‘
The inter‘ ~
bi?lar-wound transformer Ill feeds into four separately with only, a small error.
similar transformers H3. If one of these four
nels is reasonably small if the ampli?cation of
transformers is omitted as shown, a resistor 114'
about 60% '
of proper terminating value may be'substituted each/output transformer is down to If
to maintain the desired impedance match. Each
of the four transformers ! l3 in turnv is connected
curves are radically changed .when adjacent
to four more transformers H5, which also have
bi?lar-twov to‘ one step-down windings. The sec
ondary windings of these transformers H5 each
terminate'in four. resistorslll; The inputicir
transformers- are connected across the line. a
For the broadcast band the vpreviously -men-v
tioned . considerations indicating; the-“desirability:
of narrow channels apply with increased force,
' because of the greater utilization of transmission
channels within these frequencies. A band width
‘of about 350 k.‘c. has been found satisfactory.
' for this narrow band width the available gain
per stage is sufficient to require only a single
tubeper channel. The input transformers have a
gain of about 20 and the outpout transformers a
gain of. about 2. The principles involved in the
10 design of these transformers are the same as for
those of the short-wave channels.
'WhiIe the antenna structures may follow any
conventional design, we have found dipoles reso
nant to the center of each frequency band most
15, suitable for the higher frequencies. If desired,
the 2-4.6 m. 0. band may be served by a T an
of substantially different high frequencies, a plu
rality of high frequency ampli?ers each respon
sive to different bands of frequencies of the order
of 2.5 megacycles wide and including one of said
antenna responsive frequencies, means coupling
said antennas and ampli?ers having similar re
sponsive frequencies, an antenna responsive to
currents of the broadcast frequency range, a plu
rality of ampli?ers each of which are responsive
to different bands within said range of broadcast 10
frequencies, means coupling said last-mentioned
antenna and said last-mentioned ampli?ers, a
distributing network effectively connected to the
output of said ?rst and second mentioned ampli
?ers, said distributing network including a single 15
step down transformer and four similar trans
tenna, which may be coupled through a suitable . formers connected to the secondary of said single
transformer (see reference character —49) to the transformer and a plurality of step down trans
transmission line. The dipole antennas may be formers connected in groups to the secondaries of
20 erected parallel to each other with a spacing of
said four transformers, and means for attenuat
two feet and in a vertical or a horizontal plane. ing currents of predetermined frequency con
One suitable arangement is to erect a pair of sup
nected to the means coupling said last-mentioned
portsapproximately eighty feet apart. The an
antenna and said last-mentioned ampli?ers.
tenna wires are connected between these supports
2. In a system of the character described a plu
25 and are appropriately insulated to obtain the re
rality of antennas each responsive to currents of
quired effective lengths as follows: 4.6-7.3 m. 0.:
80 feet, 73-10 m. c.=50 feet; 10-12.’? m. c.=40
feet; 12.7-15.4 m. c.=30 feet and 15.4-48.1 m. 0.:
26 feet. The supporting wires on the smallest di
30 pole (26 feet) may be connected to the broadcast
antenna to increase its capacity. Likewise the
supporting wires for the dipole of a length of 40
feet’, may be used to increase the capacity of the
antenna used for 2—4.6 m. c. reception. The an
35 tennas responsive to adjacent frequency bands
are preferably spaced as‘far from each other as
possible. The foregoing antenna arrangement is
illustrated in Fig. 3.
Thus we have described a plurality of antennas
each responsive to frequencies within preassigned
channels or frequency bands. Each such antenna
isconnected to an ampli?er which is substantially
uniformly responsive to frequencies within the
I respective channels. Thebroadcast band antenna
is connected to a transmission line within which
attenuating networks may be included to reduce
interference from signal currents of great ampli
tude. The outputsrof the several ampli?ers are
connected to a common distributing network to
substantially different high frequencies, a plural
ity of high frequency ampli?ers each responsive
to dfferent bands of frequencies of the order of 2.5
megacycles wide and including one of said an
tenna responsive frequencies, means coupling said
antennas and ampli?ers which are responsive in
similar bands, an antenna responsive to currents
of the broadcast frequency range, a plurality of
ampli?ers each of which are responsive to differ
ent bandswithin said range of broadcast fre
quencies, means coupling said last-mentioned an
tenna and said last-mentioned ampli?ers, circuits
resonant to the frequency range of each of said
?rst and each of said second mentioned ampli?ers
connected to the output of said ampli?ers, a dis 40
tributing network effectively connected to said
resonant circuits, said distributing network in
cluding a single two to one step down transformer
and four transformers having a two to one step
down ratio connected to the secondary of said
single transformer and a plurality of step down
transformers connected in groups to the sec
ondaries of said four transformers, and means for
attenuating currents of predetermined frequency
which a plurality of all wave radio. receivers may
connected to the means coupling said last-men
be connected.
tioned antenna and said last-mentioned ampli
We claim:
1. In a system of the character described a plu
rality of antennas each responsive to currents
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