US1735341A - Multiple-channel communication system - Google Patents

Description

Nov. 12, 1929, A. H. TAYLOR A MULTIPLE CHANNEL COMMUNICATION SYSTEM Filed May 14, 1925 @ummm Patented Nov. 12, 19,29

'UNITED STA-TES:

Parana* OFFICE ALBERT H. TAYLOR, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, INC., OF NEW YORK, N. Y.,

A CORPORATION OF DELAWARE MULTIPLE-CHANNEL COMMUNICATION SYSTEM .Application led May 14,

My invention relates broadly to high frequency signaling systems, and more particularly to a multiple channel transmission system. l y One ofthe objects of my invention is to pro- Vide a circuit arrangement for high frequency signal transmission whereby a plurality of independent signaling circuits may be employed for independent modulation to impress signaling currents up-ona common empliication system from which the independent sets of signals may be conveyed to a carrier wave line Wire system oi' to an antenna ground radiating system.

Another object of my invention is to provide a circuit arrangement for each of a plurality of independent high frequency signaling systems for maintaining said systems at a' constant operating frequency in such manner that the systems are prevented from interacting one upon another for the multiple operation of several communication channels,

over the same line wire system or by radiation from the same antenna ground system.

Still another ob]ect of my invention is to 4provide a signaling system having a` plurality of channels for conducting communication without mutual interference over the. same carrier wave circuit or radiation circuit in which quartz `crystals of Certain definite frequencies are arranged in circuit with the transmission channels for independently controlling the frequency of each of the channels for preventing mutual reaction of one channel upon another in the process of simultaneous operation of the circuits.

Still another object of my invention is to provide independent crystal control circuits for a plurality oftransmitting circuits arranged to deliver signaling energy to the same carrier wave line wire system or to the same antenna ground system in which the crystals are groundto definite frequenciesand connected in circuit withv independent oscillators for maintainingthe oscillators at the signaling frequency free of mutual inter-action.

A further object of my invention is toprovide crystal lcontrol circuits for a multiple channel communication 'system where independent 'electron tube oscillators may be 1925. serial no. 30,252.

maintained at difierent frequencies'separated from each other by only a small percentage in frequency, while the power supply for the' electron tubes may, be derived from a common source and the oscillations impressed upon a common signaling circuit without inter-'action between the oscillations.

lVhen -my invention is employed in radio transmission, I find that the system is par'- ticularly adapted to minimize fading effects by transmitting. the same message on two simultaneous emitted frequencies. These lseparate frequencies seldom fade out simulquency is su'liicient to alter the time and the amount of fading, such a combination gives considerable protection against loss ofl a portion of the message by fading.' Vhen used for multiple channel communication for independentmessages, traffic may be routed through both of the transmitting circuits radiating independent messages simultaneously from the same antenna system. The antenna systems may be given particular direction-al characteristics in such manner that, with Ithe transmitting station located at the -Navy Department, Viashington, D. G., one

channel may be in direct communication with Europe, while another channel is in simultaneous communication with the Philippines.

My invention makes use of the constant frequency characteristics of the piezo electric effects vpcssessed by quartz crystals. I have illustratedmy invention as applied to two-A channel communication system where a pair of clectrontubes is arranged in a bilateral circuit for alternating current supply on the anodes or plates with the cathodes or filaments lighted or heated from an alternating current power supply. Two independentI yquartz crystals are prepared by grinding the crystals to two di'erent frequencies and the crystals connected around the input circuits of each of the oscillators for controlling the frequency thereof. The oscillators operate in alternation, one on one lobe of the alternating current power supply and the other on the opposite lobe of the alternating current power supply. The'outputs for the several tubes are Supplied to a common utilization circuit in a manner which will be more fully described hereinafter/and simultaneous but independent communication maintained by modulation of the oscillator circuits.

My invention will be more clearly understood from the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates a two-channel communication system embodying the principles of my invention. The circuit arrangement includes electron tubes land 2 each haying a cathode 1a and-2-, a plate or anode 1b and 2b7 and a control electrode or grid lC and 2. The high potential source for the electron tubes is derived from a common power supply system. There are two quartz crystals provided marked @C1 and QC2, one controlling the frequency of the left-hand tube 1 and the other that of the right-hand tube 2. Separate sensitizing chokes 3 and 4 are each connected in circuit y with the quartz crystals @G1 and Q02 and around the input circuit of the tubes 1 and 2. The sensitizing choke 3 has a free wavelength characteristic somewhat shorter than the frequency to which the crystal QCl is ground. Similarly, the sensitizing choke 4t has a free wavelength characteristic somewhat shorter than the frequency for which the crystal Q02 is ground. Eachv choke isplaced in series with its own corresponding crystal. The anode or plate supply for the tubes is obtained from any suitable source through line system 5 and an anode supply transformer 6 having primary winding I and secondary winding 8. It is well to use an alternating current supply of frequencies suliiciently high to give a pleasing tone to the received signals. It has been found that frequencies between 210 and 600 cycles are satisfactory for this purpose, although experiments have been made with frequencies as low as 25 cycles. The anode 1b of tube 1 has radio frequency choke 9 in series therewith and signaling key 10 is connected in the plate circuit and with one end of the secondary S. The a-node,2b of the electron tubev oscillator 2 includes radio frequency choke coil 11 in' circuit therewith and a signaling key 12 is series connected into circuit with the opposite end of the secondary winding 6. At the inidpoint 14 in the secondary winding 8 a connection is taken to the shield 15 which entirely screens the oscillator and forms a ground connection for the several circuits of the oscillator. rllhe output of the several Maasai necessary that the two quartz crystals do not differ by more than a small percentage in frequency in order to have a single adjustment of the condenser 17 suitable for Athe production of oscillations of dilferent frej quencies; one in the right-hand tube 2 and the other in the left-hand tube 1, but both pass through the common plate coil system. Suppose, for example, the circuit is operated in the neighborhood of 4000 kes-thc crystals would then differ by as much as 10 kc. from each other and only have a difference in fre quency of onesfourth of one percent. This is too small from aipercentagepoint of view to throw any of the circuits sensibly out of tune, and therefore these two frequencies are both produced in the common platecoil system with a single setting of 1T, which can be so adjusted as to bring the oscillations of the two frequencies through with substantially the sameenergy or, if desired, the emphasis can be put on one or the other of the two frequencies. It is understood of course that various forms of coupling may be used in this plate output circuit and that I do not intend the invention to be limited to the particular arrangement shown.

Any combination of plate circuit induetances may be used for deliveringthe independent oscillations to the signaling systems. lllhere coupled circuits are used however the coupling should be quite close in order that the rotation of the condenser 17 will adequately control the phase ofthe current in the plate circuit and therefore establish the correct phase relations for the development of the oscillations ofthe crystals. lt is advisable to use a certain amount of shielding as illustrated, but it is not absolutely necessary.

rllhc cathodes 1? and 2a are each heated from transformer 18 having primary winding 19 thereof supplied from the line wire system and secondary winding 20 coupled thereto. Cathode 2n is connected across the ends of the secondary winding 20 while a midpoint 21 is connected to the shield or ground 15 through conductor 22. The outputcircuits 16 and 1T may deliver signaling energy to the input circuit of a suitable power amplifier 23 from which the energy may be impressed upon a carrier wave line wire system or the antenna radiating system represented at 24 and 25. It is advisable to use a certain amount of negative C voltage in connection with crystal control oscillators. IThese negative C voltages can be obtained from the taps on the plate circuit transformer 6 with the resistances marked 26 and 27 in series with these negative C taps ony the transformer winding 8 which prevent a rush of current in the tubes l and 2 when the plate voltage and grid voltages reverse. During that half-cycle when a tube is nonoscillating, with this precaution it is perfectly possible to derive negative C voltage from' taps on the plate circuit transformer.

Resistance 27 is connected in series with radio frequency inductance 28 and supplies the proper bias potential to the grid electrode lc of the tube l. The radio'frequency choke coil 29 is connected in series with resistance 26 and supplies the proper grid bias potential to the grid electrode 2c. Each wave is modulated at the supply frequency. words, it consists of the carrier wave with the usual side bands and can be received with either oscillating or non-oscillating detector in the usual manner. If crystal control were notused the point must be emphasized that it would not be possible to receive a smooth, clean-cut signal unless the two crystals were ground identical and only one wave emitted, because the sequence of phase would be broken and the action of the lieterodyne or autodyne reception would be to give a very rough received tone like anA oscillating circuit receiving'a spark signal. But the damping of the crystals isso slight that feeble oscillations will hang over in the crystal from cycle to cycle, thus starting oif consecutive oscillation groups as first one plate, then the other becomes positive in their proper sequences of phases. This is a veryimportant point because it permits of a far superior type of reception with oscillating detector. There is also a limit as regards the frequencies of the.

two waves emitted where it is not possible to key at telegraphic speed on account of the slowness of response of the crystal. Experiments have been made between 3000 and 4000 kes. however which show that at these frequencies satisfactory keying as high as twenty-five words per minute isireadily possible and probably at considerably higher frequencies. These two frequencies are'not given off simultaneously, but in alternating groups, the

sequence'of phase in each group of frequen-l cies being maintained intact due to the property of the respective crystals, thus permitting smoothv reception with heterodyne or autodyne. No additional complications are necessary in the power amplifier and antenna circuits because these two emitted frequencies differ by so little in percentage tuning, that they will both readily pass through the power amplifier system and into the antenna.

I provide condensers 30, 3l, 32, 33, 34 and 35 at the points in the electron tube circuits,

by passing radio frequency as indicated, for

the eificiency of the currents and improving system.

It will bevobserved that, ordinarily, when In other it isattempted to operate a'plurality of oscillators anywhere in proximity of each other that the difticultyencountered is the tendency of the tubes to pull each other into step, which by the inter-actionof the circuits entirely destroys the multiple functioning of the system. By my arrangement of quartz crystal control these several circuits are maintained absolutely independent in their operation even when separated at only a small percentage in frequency. i

While I have described my invention in certain particular embodiments, I desire that it be understood that modifications may be made and that I intend no limitations upon the invention other than are imposed by the scope of the appended claims.

Vhat I claim and desire toA secure by Iletters Patent of the United States is as follows l. A multiple channel communication system comprising in combination a plurality of high frequency generators, a common energy supply system for alternately energizing said generators, a common energy utilization circuit connected with said generators, independent mechanically vibratile devices connected with each of said generators for maintaining said generators at a constant operating frequency, whereby inter-action between said generators is prevented, and means for independently controlling each of said generators for producing telegraphic signals in -said common energy utilization circuit.

,2. A multiple channel communication systein comprising in combination a plurality of high frequency energy generating circuits,'a common source of power supply for alternately energizing said circuits, a common utilization circuit for the high frequency currents generated in -said circuit, independent piezo electric devices each ground to different selected frequencies connected in each of said circuits for maintaining said circuits at sep arated operating constant frequencies. and means for controlling each of said circuits independently for impressing signaling currents of different frequencies upon said ct nimon utilization circuit.

3. A multiple channel communication system comprising in combination a pair of high frequency generators, a source of alternating current power' supply for alternately energizing each Aof said. generators, a common energy utilization circuit connected with said generators, and piezo electric devices each ground to a different operating frequency connected in shunt with each of said generators for maintaining said generators at a constant operating yfrequency separated by a small percentage in frequency, N'WherebyL slightly separated signaling frequencives may be impressed upon said common energy utilization circuit.

Il. A multiple channel communication sysof separated signaling frequencies may be limpressed upon said energy utilization circuit.

5. A multiple channel communication system comprising inicombination a pair of elecvtron tube oscillators, each of said tubes includiiw a rid filament and late electrode b 2') 7 l p f input circuits connected between the grid and filament of each of said tubes, and output circuits connected between the plate and filaments of each of said tubes, a common power supply means for alternately energizing said circuits, a common energy utilization circuit connected in said output circuits, and piezo electric crystal elements each ground to different operating frequencies connected in the input circuits of each of said tubes for maintaining the frequency of the oscillations delivered to'said energy utilization circuit at slightly separated frequencies for producing independent signaling currents in said energy utilization circuit.

G. A multiple channel communication system comprising in combination a pair of electrontubes, each haring grid, filament and plate electrodes, an input circuit for each of said tubes including the grid and filament electrodes of said tubes, an output circuit for each of said tubes including the plate and filament electrodes of said tubes, a common energy supply system for said filaments, aii energy supply system for alternately energizing the plate electrodes of each of said elcction tubes, a' common energy utilization circuit connected in said output circuit, and a constant frequency controlling circuit ccnnected in shunt with the input circuits of each of said tubes whereby said tubes generate oscillations at separated fixed frequencies for delivery of signaling current to saidcnergy utilization circuit at separated frequencies.

7. A multiple channel communication systeni comprising in combination a pair of electron tubes, each having grid, filament and plate electrodes, an input circuit for each of said tubes including the grid and-filament electrodes of said tubes, an output circuit for each of said tubes including the plate and filament electrodes of said tubes7 a common energy supply system for said filaments, an energy supply system for alternately energizing the plate electrodes of each of said electron tubes, a common energy utilization circuit connected in said output circuit, and constant frequency determining means comprising mechanical vibratile elements connected in the input circuits of each of said tubes for independently controlling the frequency of oscillations developed by said tubes, whereby signaling currents of separated frequencies areimpressed upon said energy utilization circuit.

8. A multiple channel communication system comprising in combination a pair of electron tubes, eachlliaving grid, filament and plate electrodes, an input circuit for each of said tubes including;r the grid and filament electrodes of said tubes, an output circuit foi' each of said tubes including the plate and filament electrodes of said tubes, a common energy supply system for said filaments, an energy supply system for alternately energizing the plate electrodes of each of said electron tubes, a common energy utilization circuit connected in said output circuit, and a quartz crystal circuit connected in shunt with each of' said input circuits for independently controlling the. frequency of each of said tubes, one of said quartz crystal circuits differing in frequency from the other of said quartz crystal circuits whereby signaling currents of separated frequencies are impressed upon said common energy utilization circuit.

9. A multiple channel communication system comprising in combination a pair of electron tubes, each having Orid, filament and plate electrodes, an input circuit for each of said tubes including the grid and filament electrodes of' said tubes, an output circuit for each of said tubes including the plate and filament electrodes of said tubes, a common energy supply system for said filaments, an energy supply system for alternately energizing the plate electrodes of each of said tubes, a common energy utilization circuit connected in said output circuit, and a device for sustainingv constant frequency oscillations connecte'd in the input circuits of each of said. tubes foi independently controlling the generation of a constant frequency by said tubes whereby signal currents separated from each other in frequency may be produced in said energy utilization circuit.

l0. A multiple channel communication system comprising in combination a pair of electron tubes, each having grid, filament and plate electrodes, an input circuit for each of said tubes including the `grid and filament electrodes of said tubes, an output circuit for each of said tubes including the plate and filament electrodes of said tubes, energy supply means for said filaments, a separate energy supply` circuit for alternately energizing the plate electrodes of each of said tubes, a

' common energy utilization circuit connected in said output circuit, a quartz crystal circuit connected in shunt-'With each of said input circuits and an element connected in series "Wrh each of said crystals and having a free weve-length less than the frequency of the crystal with which it is connected for independently controlling 'the requencjy1 of euch of said tubes, whereby signaling currents of separated :frequencies are impressed upon Suid common energy utilization circuit.

ALBERT H. TAYLOR,

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