US2150241A - Communication system - Google Patents

Description

March 14, 1939. H. J. NICHOLS ET AL COMMUNICATION SYSTEM Filed Feb. 23, 1955 2 Sheets-Sheet 1 R50 T/ F/ER ATTORNEYS March 14, 1939.

H. J. NICHOLS ET AL COMMUNICATION SYSTEM Filed Feb. 23, 1935 2 Sheets-Sheet 2 RECTIFIER REC T/F/ER F/LTER Pam/rm a9 lNVENTCgQf W( Eff/ 35M 9 ATTORN EYS Patented Mar. 14, 1939 UNITED STATES 2,150,241 COMMUNICATION SYSTEM Harry J.

Nichols and Henry L. Tholstrup, Dayton, Ohio, assignors, by direct and mesne assignments, to International Business Machines Corporation, New York, N. IL,

New York a corporation of Application February 2a, 1935, Serial No. 7,674 r 6 Claims.

This invention relates to communication systems, and particularly to carrier telegraph systems.

It is the principal object of the invention to 5 provide a very satisfactory carrier communication system making use of simple and economical apparatus.

A further object is to provide a carrier system having a minimum of steps or links in the system.

A further object is to provide a carrier system particularly adapted to telegraph systems utilizing signals of uniform duration but of different characteristics.

A further object is to provide a carrier system in which frequencies are generated, amplified, and the like in groups, each group being handled in such manner as to obtain compensation of certain variations in the relations between the signals of the several frequencies. 20 A further object is to provide a carrier system particularly adapted to simultaneous telephonic and telegraphic communication over the same circuit.

Other objects and features will be in part obvious and in part hereafter pointed out in connection with the following description, the accompanying drawings, and the appended claims.

In the drawings:-

Fig. 1 shows in schematic representation a preferred. form of sending circuit illustrating one aspect of the invention;

Fig. 2 shows one form of receiving circuit according to the invention;

Fig. 3 shows another form of receiving circuit according to the invention; and

Fig. 4 shows a combined sending and receiving arrangement embodying the circuits of Figs. 1 and 3.

In the several figures, like characters represent like parts.

Referring now to Fig. 1 oscillator tube To is preferably of the twin-triode vacuum tube type being provided with two grids H and I2, two anodes 2|, 22, and a common thermionic cathode l3 all mounted in an evacuated envelope M in well known manner. Power for tube To and the other tubes employed in. the various circuits is obtained from a rectifier and filter unit l5 as indicated, or from any other suitable source. The voltage divider of unit I5 is provided with the proper sections, as for example l5a, l5b, l5c, or is suitably tapped to provide the proper potentials to the various circuits of the arrangement. Oscillator tube To is provided with two tuned oscillator circuits of known type, one circuit designated by reference numeral H being associated with grid ll, while similar circuit I2 is associated with grid l 2. Inductively coupled with these circuits are feed-back circuits 2|, and 22', associated with anodes 2| and 22 respectively forming oscillation transformers 0T1 and GT2, respectively. Oscillator circuit l l is tuned to a particular frequency f1 while oscillator circuit I2 is tuned to a difierent frequency f2. These are known as the channel frequencies, and in cases where simultaneous telephone and telegraph communication are to be provided over the same circuit, these frequencies are preferably chosen in the range just above the usual audible telephonic frequencies, as for example in the range between ten and twenty kilocycles. Where telephonic communication is not involved, the frequencies are advantageously chosen in the audible range since following well known laws, the lower frequencies are more efliciently transmitted over wire circuits. The invention is not, of course, restricted to any particular frequencies or frequency ranges, nor is it restricted to the provision of two channel frequencies and circuits, as more may be provided if desired.

Grids l l and I2 are normally held at a negative bias by section l5b of the voltage divider, the bias being suificient to prevent oscillation. The normal bias is applied through resistors R11, R12, while by-pass capacitors C, C" offer a low impedanc'e return of the oscillating grid currents to cathode.

The keying equipment is connected across the grid-cathode circuits of oscillator tube To. Thus, for example, the circuit including key K1, resistor R11, and battery 13 may be regarded as the sending loop of channel one, while the circuit including key K2, resistor R12 and battery B may be regarded as the sending loop of channel two. Both oscillation circuits are coupled to the line by suitable means such as line transformer T15. Blocking capacitor C5 is provided to prevent direct current from the line saturating transformer Tr5, but is not essential on lines where stray currents are not likely to occur. The sending circuit, consisting of the secondary of T15 and C5 in series therewith is preferably bridged across the line head of telephone instruments when used. Suitable means, such as choke L5, is preferably connected in series with the telephone instruments for the purpose of impeding the passage of carrier currents in that direction while permitting the passage of voice currents to.the telephone instruments.

The operation of the circuit shown in Fig. 1 is as follows:--Normal1y oscillator tube To is prevented from oscillating by reason of the negative bias on its grids. Assume that the key K1 is closed, completing the sending loop circuit. Then current from battery B flows through K1 and R11 and return via the grounded frame, setting up a voltage across R11 opposing the bias voltage and raising the potential of grid ll sufficiently to cause To to build up oscillations in the circuit l l associated with grid H. Oscillations of frequency ii are then transferred to the line via line transformer Tr5. As soon as the key is released the original bias on grid II is returned, and the oscillations are promptly stopped. Thus a train of waves of frequency fl is transmitted over the line so long as key K1 is held down, and such carrier signals represent the signal pulses in the sending loop as regards time and duration. Assuming key K: to be depressed, the action is similar except that the potential of grid I2 is raised positively and carrier signals of frequency Ia are transmitted to the line.

It should be observed that the arrangement herein shown eliminates the need for an amplifying tube, with a consequent saving in apparatus although such amplifying means as desired may be used. It also presents a novel method of keying carrier generating apparatus. Fur thermore, since the same oscillator tube generates a plurality of frequencies, there is an inherent compensation of variations likely to occur were the frequencies generated by separate tubes. For example, a common cathode and a common atmosphere for the plural elements of the tube are conducive to uniformity of emission and space currents. As the tube ages, the constants of the tube circuits are affected in the same degree, hence the power ratio of the oscillating currents tends to remain balanced, thus maintaining a uniform ratio of the signals. The tuning and balancing of the I circuits is facilitated by the uniformity of the characteristics of the plural tube circuits. There is also asaving in power, a saving in space and in associated parts.

Referring now to form of receiving arrangement, the receiving circuit 20 is coupled to the line by line transformer T in the same manner as in the previous figure or by other suitable means. wise, inductance L5 offers a high impedance to the carrier signals in the direction of the telephone instruments with relatively minor attenuation of the voice currents. The receiving aircult!!! is divided into two branches and 20" tuned to frequencies 11 and In by series combinations of capacity and inductance, C1, L1 and C2, L2, respectively. The primaries of transformers TH and Tr2 are included in branch circuits 20' and 20", and the secondary circuits of these transformers are tuned to frequencies f1, and I: by capacitors C3 and C4 respectively. Transformers Trl and TrZ couple the tuned branch circuits to the grids of electronic relays T1 and T: as shown. The L/C ratio or ratio of inductance to capacity of the tuned circuits including C3 and C4 should preferably be small in order that the full resonant response of the tuned circuits will be somewhat delayed. This counteracts the tendency of transient impulses to trip T1 and T2.

Electronic signal translating devices comprising relays T1 and T2 are preferably of the well known triode gas-discharge tube type in which the grid trips or ionizes the tube permitting a. comparatively large ionization current to flow in the anode-cathode circuit thereof. After ionization, the grid loses control and is ineffective to terminate the discharge until the anode potential is reduced substantially to zero. Hence deionizing or cut-ofi means additional to the grid are provided when direct current is used to supply the anode circuit. Any suitable means may be used, such means being indicated by reference numeral 25. For example, a cut-oil relay Fig. 2, representing one Likemay be used in the position of when the tubes are used alternately, to effect deionization of the tube or interruption of the circuit after a brief interval of operation, thus serving both tubes, or other known means may be used. Resistors R1, R2 serve to limit the grid current upon ionization of their associated relays, while resistors R3, R4 represent the load resistances of T1 and T2 respectively. Relays L3, Lr'may represent the receiving relays for two channels, two printer actuating magnets, or any other translating means by which the telegraphic signals are recorded or rendered intelligible. Relays T1 and T2 are conveniently supplied with energy by rectifier unit H5, or from any other suitable source.

The operation of the arrangement of Fig. 2

is as follows: Assume that a train of carrier waves of frequency i1 is received from the line. Owing to the tuned filter arrangement L1, C1 in branch circuit 20', this branch offers a markedly lower impedance to the signal train than does branch 20''. Hence the voltage which ap pears across the secondary of TM is considerably higher than that across the secondary of M. Furthermore the secondary of Tri being tuned to frequency )1, While the secondary of T11 is tuned to frequency is, a further frequency selective effect is obtained. For example, under suitable conditions, for signals of frequency 11 the voltage ratio of the potential applied to the grid of T1 as compared to the potential applied to the grid of T2 may be 10 to 1, while a like ratio favorable to T2 may be obtained for signals of frequency f2. Thus by suitable choice of the operating conditions for T1 and T2, following well known practice, T1 will be exclusively tripped by signals of frequency f1, while T2 will be exclusively tripped by signals of frequency is.

Assuming that T1 has thus been tripped, a pulse of current flows (following the ordinary convention) from positive source via cut-off device 25 to the anode of T1, thence by space current to cathode, through resistor R3 to frame and return to source. The current through resistor R3 causes a potential drop across same, hence part current (in such amount as is desired) is diverted through the winding of relay L3 energizing same. After an interval determined by cut-oil, device 25, the potential across the anode and cathode of T1 is reduced substantially to zero, the potential being held down long enough to permit the grid of T1 to regain control, thus effecting the de-ionization of T1.

In similar manner, .upon the reception of a train of waves of frequency f2, T2 is ionized, relay L1 is energized and cut-off device 25 causes the deionization of T2 thus restoring the circuit to normal condition.

It should be noted that the cut-off device operates to effect deionization after a definite, predetermined interval, hence the translating devices are energized for the same duration by all signals of amplitude suificient to ionize the electronic relays. The invention is thus particularly suitable to equal signal systems, and in such systems has the practical advantage of providing reliable operating impulses even though the received signals may be clipped or mutilated.

The arrangement here shown is very desirable in that among other advantages, it eliminates the need for a detector and/or amplifying tube,

the electron relays which perform the .usual function of a line relay being actuated directly by the incoming signals. It is characterized by its simplicity-and advantageous use of electron relays. In addition to the selective action of the tuned receiving circuits, further selective action is obtained by the novel method of selective tuning of the electron relay input circuits.

Referring now to Fig. 3 which shows another form of receiving arrangement in accordance with the invention, selection as to frequency is accomplished in steps, the first of which occurs in the coupling circuits of tube T whichhere functions as a signal amplifying tube. The arrangement'shown is particularly suitable for use on lines where the attenuation is considerable and/or where the channel frequencies are narrowly spaced. The secondary circuit 20 of line transformer Tr has two branch circuits 20', 20" including coupling coils 2|, 22' of transformers O'Ifi and GT2, these branch circuits being selectively tuned to frequencies )1 and f2 by suitable means such as filter arrangements S1,L1andQ2,L2'. The secondaries of OTI and GT2 are also tuned to frequencies f1 and f2 respectively, and apply potential variations corresponding to the carrier signals to grids H and I2 of tube To. The primaries of transformers Trl and Tr2 are included in plate circuits 3| and 32 associated with plates 2| and 22 respectively. The remainder of the arrangement is as described in connection with Fig. 2.

The operation is as followsz-Carrier signals from the line are transferred by line transformer Tr5 to branch circuits 20' and 20", but in unequal degree depending upon the carrier frequency, as for example signals of frequency h are offered a low impedance path by fil ter combination L1, 01 and a high impedance path by filter combination L2, C2, hence the major portion of the energy flows in circuit 20. For signals of frequency f2 the reverse holds. Further selective action occurs in tuned circuits H and i2 improving the voltage ratio of the potentials applied to grids H and I2. Tube To amplifies the signals, which are applied with augmented amplitude to the primaries of transformers TH and Tr2. With proper operating conditions, T1 will thus be tripped by h signals, and T2 by fz signals, producing selective operation of translating devices L3 and L4.

This arrangement is characterized by its high selection ratio, its ability to function reliably on weak signals, its economy of apparatus, and the inherent compensatory features of the twin amplifying tube employed.

It should be noted that amplifying tube To has the beneficial effect of increasing the selection margin. As-is well known, electron relays such as T1 and T2 here employed are tripped by a certain critical value of potential. For example, let it be assumed that each tube can be tripped by a peak potential of twenty volts applied to the primaries of Tri and T72. Let it further be assumed that the selection ratio due to tuned circuits L1, C1, and L2, 02 and tuned transformers QTl and GT2 is ten to one, and that the effective amplification factor of To is five. Then if the peak voltage on grid it due to a fi signal is volts, that on grid 52 will be one volt, giving a selection margin of nine volts. After amplification by tube To, these peak voltages become 50 volts andb volts respectively, giving a selection margin of 45 volts. This voltage difference, applied to T1 and T2 bytransformers TM and TrZ, provides a substantial operating margin for selection purposes. It is to be understood that the voltage values cited in the example are for illustrativepruposes, and in practice reliable selec tive action can be obtained with comparatively feeble carrier signals, and widely varying selective ratios.

Referring now to Fig. 4, a combined sending and receiving arrangement is shown which is particularly adapted to two way systems in which communication is held in one direction or the other, but not simultaneously in both directions. This arrangement represents a combination of those shown in Figs. 1 and 3.

Suitable switching means, designated by S, Si,

S2, S3, are provided to change the circuits at will from sending to receiving condition. The switches are shown at convenient places in the diagram, but in practice are conveniently grouped in a single multiple switch. It is assumed that when the switch tongues are moved to the right, the circuits are in sending condition and when moved to the left are in receiving condition. ,Assuming first that sending conditions are to be established, all switch. tongues are to be considered as being to the right. Switch S then applies positive potential to plate 2| via lead 20, primary of Tr5, branch 20 and coil 2|, via switch SI, and thence to plate 2|; and to plate 22 through the circuit including the primary of Tr5, thence through branch 20" and coil 22, via switch S2 to plate 22. Switch S3 connects the sending device, such as printed 34, across grid resistor R via lead 4|, and across grid resistor R|2 via lead 42. A printer which has been found to give very satisfactory results is that disclosed in our copending application Serial No. 738,833, filed August 7, 1934;

The sending operation is the same as described in connection with Fig. 1, except that printer 34 functions in the same manner as but replaces the keying arrangement comprising Kl, K2, and B of Fig. l. Briefly, one portion of the printer circuits is associated with OTI and the other portion with 0T2. When one of the printer keys is operated, the tube To is-placed in oscillation at the selected frequency, f1 or f2, and for the proper duration and at the proper time in accordance with the particular key operated, a corresppnding signal being sent over the line.

Assuming next that receiving conditions are to be established, all switch tongues are moved to the left. Switch S connects lead 20 to, the mid point between Cl, C2; switch Sl connects plate iii to lead 3|, and coil 2| to L|; while switch S2 connects plate 22 to lead '32 and coil 22 to L2, thus completing the signal circuits as described above in connection with Fig. 3. Switch S3 connects printer 34 to leads 5% and 52 which are included in the output circuits of electron relays Ti and T2.

The receiving operation is the same as that described in connection with Fig. 3, except that printer 3t functions in the same manner as but replaces the translating devices L3, L4 of Fig. 3. Thus the signals, distinguished by their frequency, time, and/or duration, are caused to effect the selective operation of the printer and to cause operation of the printer keys corresponding to those at the sending station.

The arrangement is characterized by its dual utility, relative simplicity, and balancing and compensating features.

It ll be apparent that the arrangements shown in Figs. 1 and 2 can be combined into a sending-receiving unit in the same general manner as the arrangements of Figs. 1 and 3 have been combined, and in some applications may be preferable to that shown in Fig. i. detailed connections for such combination will readily be seen by those skilled in the art, hence further description is not required.

The advantages enumerated, and others unmentioned, are attributable to the method of handling the channel frequencies in groups, to the use of a multiple tube with balanced elements, to the advantageous use of electron relays in combination with frequency selective circuits, and to the novel arrangements disclosed. It will be apparent that the invention provides a carrier signalling system which is relatively simple, economical in the use of apparatus, efllcient and reliable in action, and which meets in a highly satisfactory manner the manifold and exacting requirements for a system of this type.

While the methods herein described and the forms of apparatus for carrying these methods into eifect constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

,What is claimed is:

1. In carrier signalling systems, a carrier frequency selective receiving arrangement comprising a plurality of frequency selective receiving circuits each tuned to a particular frequency, a plurality of electron discharge tubes each provided with a control grid and adapted to be substantially completely ionized upon the direct application of a signal having a critical value of potential to its control grid, magnetic coupling means for coupling said selective receiving circuits to the grids of said discharge tubes, said magnetic coupling means being provided with a tuned secondary circuit characterized by an L/C ratio adapted to retard the resonant response of said tuned circuit, a plurality of signal translating means each operatively associated with the discharge circuit of one of said discharge tubes, a source of direct current for applying operating potential to said discharge tubes, and discharge current terminating means associated with said discharge tubes adapted to produce deionization of said discharge tubes.

2. The arrangement specified in claim 1 in which the magnetic coupling means for coupling the selective tuned receiving circuits to the grids of the discharge tubes have the grid circuits tuned to the same frequency as the receiving circuits.

3. A carrier signaling system comprising, in combination, wave generating meansincluding an electron tube having a plurality of grid and anode elements mounted in a common sealed envelope and including individual circuits connected to said elements adapted to generate oscillations of a plurality of predetermined frequencies, an energy source for said tube, individual oscillation circuits included in each of ing means upon operation of any one of the.

keying means thereby conditioning the selected grid circuits to provide for the generation of oscillations of a selected one of said predetermined frequencies as long as the selected keying means remains operated.

4. In a carrier telegraph system a twochannel receiving arrangement including, in combination, two selective receiving circuits each tuned to an individual frequency, selective signal translating means, and selective signal amplifying means including an electronic amplifying tube ,provided with twin control grids connected respectively in said selective receiving circuits and also having twin anodes, said grids and anodes being immersed in a common atmosphere and sealed in a common envelope, two electronic discharge tubes each provided with control grids and adapted to be ionized uponthe application of a critical value of potential to their control grids, and individually tuned magnetic coupling means .for coupling the anode circuits of said amplifying tube to the control grids of said discharge tubes, said tuned circuit of the magnetic coupling means being characterized by a controlled small L/C ratio adapted to retard the resonant response of said tuned circuit.

5. In carrier signal terminal apparatus adapted to function selectively for sending and receiving, in combination, an electronic discharge device having a plurality of grid and anode elements mounted in a'common sealed envelope and including individual circuits connected to said elements, individual tuned circuits included in each of the grid circuits and including means for normally conditioning the device to prevent current flow in the anode circuits, individual keying means included in the said grid circuits and signal translating means controlled by the said anode circuits, positionable switching means to condition selectively the said device and said associated circuits whereby in one position the keying means are effective to initiate selectively carrier signals of predetermined frequencies and in another position condition the same said elements of the device and associated circuits to amplify selectively signals of the aforesaid predetermined frequencies on receiving thereby controlling selectively the operation of the said translating means.

6. In carrier signal terminal apparatus adapted to function selectively for sending and receiving, in combination, signal translating means, selectively tuned electronic relay means adapted to selectively actuate said signal translating means, an electronic discharge device having a plurality of grid and anode elements mounted in a common sealed envelope and including individual circuits connected to said elements, individual tuned circuits and individual keying means included in each of the grid circuits, and positionable switching means to condition selectively the said device and associated element circuits whereby in one position selective operation of the keying means are effective to initiate selectively carrier signals of predetermined frequencies, and in another position condition the same said elements of the device and associated circuits to amplify selectively signals of the aforesaid predetermined frequencies thereby controlling selectively the operation of the said electronic relay means and associated translating means.

HARRY J. NICHOLS. HENRY L. THOLSTRUP.

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