Title:
Diversity signaling system
United States Patent 2303493


Abstract:
"-This invention relates to selective systems of -communication, and especially to a system in which a message is conveyed by a plurality of channels. The invention provides for the normal reception on each of the channels, and provides further for automatic means for cutting out of operation...



Inventors:
Purington, Ellison S.
Application Number:
US33567240A
Publication Date:
12/01/1942
Filing Date:
05/17/1940
Assignee:
RCA CORP
Primary Class:
International Classes:
H04B7/12
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Description:

"-This invention relates to selective systems of -communication, and especially to a system in which a message is conveyed by a plurality of channels.

The invention provides for the normal reception on each of the channels, and provides further for automatic means for cutting out of operation :any channel that is being interfered with.

It further provides that in case any channel is interfered with and thereby withdrawn from operation, then the sensitivity of channels not being interfered with automatically increases, to make the resulting signal strength substantially independent of the withdrawal of the channel interfered with.

This invention is illustrated for a specific type of signal, namely, a tonally modulated signal such as in radio telephony or in tonally modulated telegraphy. Furthermore, the channels used are regularly spaced on a frequency basis. This arrangement is for illustration only, and the invention applies regardless of the frequency allocation of the channels: and the nature of the signals conveyed. The only restriction is that each channel shall convey the same signal.

The term channel is further not to be considered synonymous with wave band, since channels may be made up by depending upon energy from widely separated wave bands. Thus, for example, with four radiated frequencies a, b, c, and d, a receiver may be devised if desired with six channels, involving tuning to the difference between each radiated frequency and every other radiated frequency.

For purposes of illustration, however, each -channel is identified with a single wave band, making up a part of a broader wave band, and in particular the signal herein used is produced by frequency modulation at a high audible or low ..superaudible rate, in combination with amplitude modulations at a low audible rate.

The invention also consists in certain new and ,original features of construction and combina.tions of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be :particularly pointed out in the claims appended hereto, the invention itself, as to its objects and ;advantages, the mode of its operation and the .manner of its organization may be better under:stood by referring to the following description ,taken in connection with the accompanying drawings forming a part thereof, in which Fig. 1 illustrates diagrammatically a trans- : mitter constructed in accordance with the invention; Fig. 2 shows the spectral distributions of the emitted radiations; Fig. 3 illustrates diagrammatically a modified form of transmitter in which the carrier is fixed; Figs. 4, 5 and 6 illustrate the operation of the transmitter; Fig. 7 depicts diagrammatically the general features of a five channel receiver; and, Fig. 8 shows a typical diagram of one of the five channels depicted in Fig. 7.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawings, Fig. 1 shows a transmitter which includes a carrier energy generator 11, a modulation frequency oscillator 12, a power amplifier 13, a modulator 14, a preamplifier 15 and an antenna system 16.

The carrier energy generator 11 includes a triode tube 11 which is provided with a plate tank circuit 18 and a feedback coupling coil 19 to produce high frequency oscillations in a well known manner, which are adjusted by a variable condenser 20.

The oscillator 12, which is of well known and standard construction, is provided with an output coil 21 which is coupled to a plate coil 22 and a grid coil 23, which are shunted by condensers 25 and 26 respectively. The plate coil 22 is connected through a choke 27 to the tank circuit 18 and the grid coil 23 is connected through a choke 28 to the grid of the tube 17.

The power amplifier 13 includes a pentode tube 30 the first grid of which is connected through a condenser 31 to the output circuit of the tube 17.

An inductor 32, a condenser 33 and a resistor 34 serve to bias the grid of the tube 30 and to permit 45 radio frequency voltage to be established thereon.

The output circuit of the tube 30 includes a tank circuit 35 and the secondary of a transformer 36 the primary of which is included in the output circuit of the modulator 14. The input 0 circuit of the modulator 14 is connected through a transformer 37 to the output circuit of the preamplifier 15, the input circuit of which is connected to a microphone 38.

The tank circuit 35 is coupled to a coil 40 which ;5 is connected through a condenser 41 to the antenna IS, the coil 40 and condenser 41 forming a tuning circuit.

Operation The characteristics of the high frequency oscillations produced by the generator I are varied by the output of the modulation frequency oscillator 12, as energy from this oscillator is inserted by the coupling coil 22 into the plate circuit of the tube 17 and by the coupling coil 23 into the grid circuit of the tube 17. With the ratio of the couplings properly chosen, the oscillations generated by the tube 17 will be frequency modulated at the frequency generated by the modulator 12 in a manner similar to that described in my U. S. Patent 1,599,586. The output of the frequency modulated tube 17 comprises the equivalent of a plurality of continuous waves separated in frequency by an amount *equal to the frequency generated by the modulator 12. This output serves as the carrier waves of the plurality of channels.

The output of the tube 17 is impressed through the condenser 31 upon the first grid of the tube 30 of the power amplifier 13 which is plate modulated by the microphone 38 acting through the preamplifier 15 and modulator 14. The modulated output of the power amplifier 13 is transferred to the antenna 16 by means of the tank circuit 35 and antenna tuning circuit 40-41.

These elements may be so designed as to reenforce the higher order side bands at the expense of the lower order sidebands so that substantially equal energy is radiated on each channel.

The spectral distribution of the energy radiated by the antenna 16 may, for example, be as depicted in Fig. 2. As previously stated the energy on the channels may be equalized by choice of the antenna system or by other devices such as an equalizer between the carrier energy generator 11 and the power amplifier 13. This figure depicts the effect of frequency modulating a carrier wave at a relatively high modulating frequency and then amplitude modulating the reSsultant wave form at a relatively low modulating frequency. The result is a plurality of continuous waves each amplitude modulated by the same signal.

As an alternative a plurality of continuouE waves could be independently established by s plurality of crystal controlled oscillators and the waves radiated from a plurality of antennas coul be amplitude modulated all in accordance witl the same signal.

The modified form of transmitter depicted ir Fig. 3 comprises a crystal controlled oscillator 45 a buffer circuit 46, a phase splitting circuit 47 an electronic mixing amplifier 48, a push-pul modulator 49, a high modulating frequenc: source 50, a distorting circuit 51, a limiting cir cuit 52, a power amplifier 53, a modulator 54 an a preamplifier 55.

The oscillator 45 includes a triode tube 57, piezo-electric crystal 58 and an output tank cir cult 59 which is connected through a condense 60 to the first grid of a pentode tube 61 whic] forms part of the buffer circuit 46. The plat circuit of the tube 61 includes a tank circuit 6which is connected through a condenser 63 t the phase splitter 47.

The phase splitter 47 comprises a condenser -6 two resistors 66 and 61 in series with two coil 68 and 69 mounted at right angles to each othe and an output coil 70 adjustably mounted in th space between the coils 68 and 69.- One side c the coil 10 is connected through two condensers 71 and 72 to the push pull modulator 49.

The mixing amplifier 48 is shown as including two pentode tubes 13 and 14 and a tuned output tank circuit 75. The first grid of the tube 73 is connected to the phase splitter 47 and the first grid of the tube 74 is connected through a transformer 76 to the cathode output circuit of push pull modulator-49, the plates of which are connected through chokes 11 and 78 and transformer -79 to the modulating source 50.

The output circuit of the mixing amplifier 48 is connected through a condenser 81 to the grid of a triode tubei 82: which forms part of the distorting, circuit 51 and which may be biased near cut off similar to a detector tube. The output circuit of tube 82 includes a tuned tank circuit 83 which is connected through a condenser 85 and resistors 86 and 87 to the limiting circuit 52 which comprises two diode tubes 88 and 89 in reverse connection.

The limiting circuit 52 is connected to the first grid of a pentode tube 90 which forms part of. the power amplifier 53 and the output circuit of 5which includes an output tank circuit 9. The modulator amplifier 54 is connected through, a transformer 92 to the power amplifier 53 and by a transformer 93 to the preamplifier 55. ..A microphone 95 is connected in the input circuit of the preamplifier 55. The output tank circuit 91 is coupled to an antenna circuit 96 including.an antenna 97.

Carrier frequency determining energy is generated by oscillator 45 which is stabilized by the piezo-electric crystal 58 and is tuned by the tank circuit 59. Energy from this circuit is impressed upon the buffer circuit 46 and thence through condenser 63 to the phase splitting circuit 47.

By means of the adjustable rotor 10 the phase across this rotor may be adjusted to any desired relation to the phase across any fixed part of the system, such for example as the coil 69.

Voltage from the coil 69 is impressed upon the grid of tube 73 while voltage from the rotor 70 S4 is impressed upon the push pull modulator. 49 S from which the side band output energy is impressed upon the tube 74. The push pull modulator is of -the diode type, the operation of which S is explained in copending U. S. Patent applica6.50 tion Serial No. 283,020, filed July 6, 1939, for Producing side band energy with the carrier absent.

It is thus seen that carrier determining energy from the source 45 and first order side band 1 55 energy from the source 45 push pull modulated by the source 50 are impressed upon the tubes , 73 and 74 respectively. These energies are aml plified and combined in the tank circuit 75. y By adjustment of the rotor 70 the combined - carrier determining wave and the bands may be 0 related as the central wave and first order side frequencies of a phase or frequency modulated a continuous wave; that is the phase of one side band is 1800 different from what it would be if r 65 the three constituents represented an amplitude h modulated wave. This process of producing e "quasi-phase" modulated energy is described in , detail in U. S. Patents 1,935,776 and 1,976,393, o issued to John Hays Hammond, Jr. The nature S70 of the tank circuit energy is depicted in Fig. 4. 5, The output of the tank circuit 75 is impressed s through condenser 81 upon the grid circuit of the r distorting tube 82. As a result of the distortion e effects produced in the circuit 51 there appear if ;7s currents among-others in the plate circuit of the tube 82 with frequencies centered at double the frequency of the central input frequency. In addition to the central frequency there are two orders of side bands as depicted in Fig. 5, with the central wave and side bands arranged as in phase modulation. The output tank circuit 75 is tuned to the vicinity of this double frequency.

This more complex modulated wave form may be impressed upon further distorting and limiting devices, such as the diode tubes 88 and 89 which cut off the peaks of the impressed waves and tend to develop further order side bands, so that the distorted wave more nearly approaches a true phase modulated wave form.

This process of limiting is shown for example in U. S. Patent No. 1,560,206, issued to Emery Leon Chaffee and as applied to minimizing amplitude modulation is shown by devices 28 and 29 of Fig. 2 in U. S. Patent No. 1,977,439, issued to John Hays Hammond, Jr.

The plurality of continuous wave equivalents produced by this method are impressed upon the tube 90 and after amplification are modulated at speech or other tonal frequencies from plate modulation transformer 92 which is driven by modulation amplifier 54 from preamplifier 55 actuated by microphone 95. This modulated energy is impressed by the plate to antenna coupling system, comprising the tank circuit 91 and antenna circuit 96, upon the antenna 97. It is to . be understood that the coupling and antenna systems may be so arranged as to reenforce the side band energy at the expense of the carrier to make the energies on the various channels substantially equal, as indicated in Fig. 6. 3 While means have been shown for producing five channels each modulated by the same audio frequency signal, it is to be understood that the number of channels could be increased to any desired amount by the use of successive distor- 4 tions. Other systems could, as above stated, be readily devised to provide other than the simply related channels here indicated.The signals radiated from the transmitters shown in Figs. 1 or 3 may be received and interpreted by a receiver of the type depicted in Fig. 7 in which the five channels are designated by block diagrams, an illustrative example of one of which is shown in Fig. 8.

The receiver shown in Fig. 7 comprises an antenna 100, a beat detector 101, an oscillator 102, five channels 103-107 and a set of head phones 108.

The antenna 100 is connected to the tuned 5! circuit 110 which in turn is connected to the first grid of a pentagrid tube 11l, which forms part of the beat detector 101. The third grid of the tube II is connected to a tap on the grid coil 112 of the oscillator 102. The grid coil 112 6 is inductively coupled to the plate coil 113 and 0 a vernier condenser 115 is connected between the plate and ground.

Connected in the output circuit of the beat detector 101 is a primary tuned circuit 116 which is inductively coupled to a secondary tuned circuit 117. The secondary circuit 117 is connected to bus conductors 118 and 119 which are connected to the input terminals 120 and 121 of the five channels 103 to 107. The grid return end of the circuit 110 is connected through a resistor 122 to bus conductor 123 which is connected to the automatic volume control terminals 125 of the five channels 103 to 107.

The output terminals 126 and 127 of the five channels 103 to 107 are connected to bus conductors 128 and 129 respectively, which in turn are connected to the headphones 108.

In Fig. 8 is shown a possible arrangement of one of the five channels, the others being preferably similar except as to the circuit constants.

Each channel comprises an amplifier 131, a detector 132, a second amplifier 133 and a rectifier 134. The input terminals 120 and 121 are shunted by a potentiometer 136 the adjustable contact of which is connected through a condenser 137 to the first grid of a pentode tube 138 which forms part of the amplifier 131. The grid *of this tube is connected to ground through a resistor 140 and a condenser 141.

Connected in the plate circuit of the tube 138 is a primary tuned circuit 142 which is coupled to a secondary tuned circuit 143 which in turn is connected to the rectifier portion of the tube 145 forming part of the detector 132. A resistor 146, shunted by a condenser 147, is included in the rectifier circuit. One end of the resistor 146 is connected through a condenser 148 to the grid of the amplifier portion of the tube 145 which is suitably biased by a battery 149. The output circuit of the tube 145 is connected thrugh a transformer 150 to the output terminals 126 and 127.

The adjustable contact of the potentiometer w 136 is also connected to the first grid of a pentode tube 151 forming part of the amplifier 133 the output circuit of which includes a tuned circuit 152. The plate of the tube 151 is connected through a condenser 153 to the plate of Sa diode tube 155 forming part of the rectifier circuit 134. A resistor 156 is connected between ground and the plate of the tube 155 which is also connected by a resistor 157 to the junction of resistor 140 and condenser 141. The cathode of the tube 151 is connected to ground through a potentiometer 158 the adjustable contact of which is connected through a resistor 159 to the cathode of the tube 155.

5 In the receiver shown in Figs. 7 and 8 the incoming signals from all the channels of the transmitter depicted in Fig. 1 or Fig. 3 are received by the antenna 100 and are transmitted through the tuned circuit 110 to the beat detector 101 Swhere they are impressed upon the first grid the tube Ill. Heterodyning energy of suitable strength from the oscillator 102 is impressed upon the third grid of the tube III which is suitably biased. The oscillator vernier condenser 115 is suitably adjusted so that the output of the tube III, representing the incoming signal suitably matches the characteristics of the subsequent circuits. The method of frequency conversion by the use of the oscillator 102 and associated circuits is well known and need not be more fully described herein.

The output energy of the beat detector 101 is impressed upon the primary tuned circuit 116 and inductively into h car the secondary tuned circuit 117. This energy is similar to the impressed antenna energy except as to the change of frequency. The output energy of the circuit 117 is impressed upon the bus conductors 118 and 119 and is distributed to the input terminals 120 and 121 of the five channels 103-107.

Referring to Fig. 8, relating to a selective system corresponding for example to the next to the last channel of Pig. 6, the energy received at the terminals 120 and 121 is impressed upon the potentiometer 136 from which part of the energy passes through the condenser 1-37 and is impressed upon the first grid of the amplifier tube 138 which is biased by voltage existing or developed across condenser 141. The amplified enl t~C 4. ergy corresponding to tne aesirea chnaniu s olectively transferred through the coupled circuits 142-143 to the rectifier portions of the detector tube 145 the rectified output from which passes through the resistor 146 in the direction of the arrow. This rectified energy serves to produce tonal energy for signal purposes and D. C. energy for volume control purposes. The tonal energy is transferred through the condenser 148 and is impressed upon the grid of the. amplifier portion of the tube 145, which is suitably biased by the battery 149. The output energy of the tube 145 passes through the transformer 158 to the output terminals 126 and 127 and thence along bus conductors 128 and 129 to the headphones 18; (Fig. 7).

The direct voltage developed across the resistor 146 is fed back through resistor 144 to the terminal 125, thence combined with direct voltage similarly developed in other channels is fed along bus conductor 123 and resistor 122 to the grid circuit of the tube I i to operate as an automatic volume control of the prior circuits in a well known manner.

For controlling the operation of the amplifier 131 some of the energy from the potentiometer 136 is impressed upon the grid of the amplifier tube 151. The amplified energy from the amplifier 133 corresponding to that transferred through circuits 142-143 is selectively transferred through the tuned circuit 152 and is impressed through the condenser 153 upon the plate of the diode rectifier tube 155. The cathode of the tube 155 is positively biased by the potentiometer 158 which carries the cathode-ground current of the tube 151.

The adjustment of the potentiometer 158 may be made so that for a normal signal no rectification will be produced by the tube 155. If, however, an abnormal amount of energy passes through the circuit 152, indicative of interference upon this particular channel, then the rectifier 134 operates to develop a negative voltage on the plate of the tube 155 with respect to ground due to the flow of rectified current through the resistor 156 in the direction of the arrow. This negative potential is impressed through the resistors 157 and 140 upon the grid of the tube 138 increasing the bias in accordance with the intensity of the interference, thereby reducing the amount of signal and also the interference which is delivered from the tube 145 to the headphones 108.

Because the control of the grid of the tube 138 is from a separated channel and not the output of the tube 138, as is usual in automatic volume control arrangements, the tube 138 may b( biased so that with strong interference, no signa whatever will pass through this channel. Ii the absence of signal through the channel thi voltage developed across the resistor 146 falls of so that it contributes little or nothing to the auto matic control voltage impressed back upon th preceding tubes, such as tube III of Fig. 7. There fore the bias on the preceding tube diminishe and the signal available for the other channel increases. In this manner the signal to the hea phones 108 will remain substantially constant a long as there is one clear channel on which ab normal interference does not exist.

Under normal operation the various potentiom eters 136 of the five channels 103-107 are so adjusted that each of the five channels contributes substantially the same amount as every other channel to the output signal.

S It is to be understood that the receiver shown is for purposes of illustration only. Further amplifiers and selective devices may be used to improve the performance and- operation. For example while the present arrangement utilized linear first detector 101 and amplifiers 131 and 133 at levels not readily subject to overload, under abnormal conditions the tubes 138 and 151 which are exposed to interferences which exist on other channels might be paralyzed. In this case a design in which the input to each channel, such as shown in Fig. 8, is protected by tuned circuits would be preferable by which the system could be paralyzed only by interferences which have the same frequency ranges as the channel normally transmits.

These and other modifications are omitted for simplicity and would occur to anyone skilled in the art in the development of a system of this broad type.

- Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction but might be embodied in various forms without 30 departing from the spirit of the invention or the scope of the appended claims.

I claim: 1. The method of signaling which includes the steps of producing a carrier wave, producing a modulation frequency wave, frequency modulating the carrier wave by the modulation wave to produce a plurality of continuous waves separated in frequency by an amount equal to the frequency of the modulation wave, producing signal 10 energy, amplitude modulating the resultant plurality of continuous waves by the signal energy, reenforcing the higher order of side bands at the expense of the lower order side bands so that substantially equal energy is available on each channel and transmitting the resultant energy.

2. In a signaling system wherein a plurality of continuous waves each of a different frequency are modulated by the same signal energy and transmitted, means for receiving the transmitted energy including a main channel for transmitting all of said waves, a plurality of translating channels one for each of the received waves, said main channel being coupled to said plurality of channels, means for appreciably decreasing the sensitivity of any one of said plurality of channels when the magnitude of the energy fed thereto exceeds a predetermined value, and means in said one channel for automatically increasing the sensitivity of the main channel, as the sensitivity - of the one channel is reduced, to such an extent S that the total signal output from said plurality of 1 channels remains substantially the same.

n 3. The steps in a method of signaling which S comprise, producing carrier frequency energy, f 65 splitting the phase of the produced energy, - producing a modulating frequency wave, modue lating one of the split phases by the modulating - frequency wave to produce therefrom first order s sideband output energy, combining carrier fres 70 quency energy with the resultant first order sided band output energy, the phase which is modus lated being adjusted so that the combined carrier determining wave and the first order sideband output energy may be related as the central wave -. 75: and first order side frequencies of a timing modu2,303,493 lated continuous wave, distorting the combined energy to such an extent that there result currents with frequencies centered at double the frequency of the central wave and two orders of sidebands with the central wave and sidebands arranged as in phase modulation, modulating the resultant energy in accordance with signal energy and transmitting the energy thus modulated, 4. The additional step in the method described in claim 3 which comprises reenforcing the higher order of sidebands of the signal modulated energy at the expense of the lower order of sidebands, 5. In a diversity broadcasting system including transmitting means for transmitting a plurality of carrier waves of different carrier frequencies all modulated by the same signal, a diversity receiver for receiving the transmitted waves, said receiver including an electronic tube amplifier having an input circuit upon which the received waves are impressed and an output circult, a plurality of signal translating channels, one for each of said waves coupled to said output circuit, each of said channels including means for applying to said electronic tube amplifier a biasing potential the magnitude of which depends upon the strength of signals passing through the channel, means in each of said channels for substantially suppressing translation by said channel when the amplitude of the energy transferred to said channel from said amplifier exceeds a predetermined value, and means controlled thereby for correspondingly varying the biasing potential applied to said tube by said channel in a direction to increase the amplification of said amplifier.

6. In a diversity broadcasting system including transmitting means for broadcasting a plurality of modulated continuous waves of different carrier frequencies but all modulated by the same signal, a diversity receiver for receiving the transmitted waves, said receiver including an electronic tube amplifier having an input circuit upon which the received waves are impressed and an output circuit, a plurality of signal translating channels one for each of said waves coupled to said amplifier output circuit, each of said channels including means for providing said electronic tube amplifier with a biasing potential to control the amplification characteristics of said amplifier, the biasing potential supplied by each of said channels to said amplifier being determined by the signal current passing through the channel, the total biasing potential applied to the amplifier when all of said channels are in normal operation controlling the amplification of said amplifier so as to produce a predetermined desired total output from said channels, means in each of said channels for varying the translation by the channel inversely with the amplitude of the energy transferred to said channel from said amplifier circuit, each of said means acting to substantially suppress translation in its corresponding channel when the magnitude of energy transferred to said channel from said amplifier circuit exceeds a predetermined value.

7. In a signaling system, means for generating a carrier frequency wave, means for frequency modulating the generated carrier at a relatively high modulating frequency to thereby produce a plurality of continuous waves separated in frequency by an amount equal to the frequency of the modulation wave, means for amplitude modulating the resultant waves at a relatively low modulating signal frequency to thereby produce a plurality of continuous waves each modulated by the same signal, means for transmitting the waves so modulated, means .for receiving the transmitted waves and separating out each channel, means for detecting each of the waves in the channels to produce therefrom the signaling energy, means for combining and reproducing the signaling energy.

8. The arrangement described in claim 7 characterized by that each of the channel detecting means includes means for reducing transmission therethrough when the input signal thereto becomes excessive and automatically increasing the sensitivity of the other channels to such an extent as to make the final signal independent of the number of channels operated.

ELLISON S. PURINGTON.