US2495826A - Locking and control circuit in a diversity telegraphy receiver - Google Patents

Description

R. E. SCHOCK LOCKING AND CONTROL CIRCUIT IN A DIVERSITY TELEGRAPHY RECEIVER Jan, 31, 1950 2,495,826

Filed Sept. 18, 1946 3 Sheets-Sheet 1 l'wia-s Mam/Va 67/?60/7' 7 mam/6 V V area/r INVENTOR BY A/ ATTORNEY R. E. SCHOCK LOCKING AND CONTROL CIRCUIT IN A DIVERSITY Jan. 31, 11950 TELEGRAPHY RECEIVER Fild Sept. 18, 1946 3 Sheets-Sheet 2 ATTORNEY R. E. SCHOCK LOCKING AND CONTROL CIRCUIT IN A DIVERSITY Jan. 31, 1950 TELEGRAPHY RECEIVER 3 Sheets$heet 5 Filed Sept. 18, 1946 um J INVENTOR brtEJciwc/f ATTORNEY Patented Jan. 31, 1950 LOCKING AND CONTROL CIRCUIT IN A DIVERSITY TELEGRAPHY RECEIVER Robert E. Schock, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September 18, 1946, Serial No. 697,669

2 Claims.

siderable extent in connection with pulse systems Where they are driven by pulses of one form or another fed to the trigger circuit through one or more condensers. When it is desired to use a trigger circuit for something other than the transfer of or the shaping of pulses, it may be desirable to drive said circuit from What may be called a slow varying direct current potential. In such a case, a problem is presented in finding a satisfactory method of applying the varying direct current potential to th locking circuit without destroying its triggering or looking properties.

It is an object of the present invention to improve unidirectional potential drivers gering or looking circuits.

This object is attained in accordance with my invention by the use of a control or driver tube, the anode circuit of which includes a resistor, also included in the anode circuit of one of the locking circuit tubes. The driver tube is controlled by the unidirectional potential and the condition of stability of the trigger or looking circuit is controlled by the magnitude of potential drop in the common resistor.

Since the locking circuit is by necessity'controlled by a driver tube connected therewith, the driver tube per se unbalances the trigger circuit to a certain extent to cause its switching action to be non-symmetrical or unbalanced.

A further object of my invention is to provide means for compensating or correcting this unbalanced condition. This object is attained by provision of a second tube connected to the other locking circuit tube substantially in the same manner in which the driving tube is connected to the first locking circuit tube. The compensating tube is then held at a selected bias so that complete balance is attained when a selected unidirectional control potential is applied to the driving tube.

In a modification of my invention as described above, two driver tubes are used, one connected with each locking circuit tube so that the driver tubes balance each other in the locking circuit.

Differential unidirectional potentials are then for trig- CJI 2 used in a novel manner to control the driver tubes which in turn control the condition of stability of the locking circuit.

As indicated above, the improvements disclosed herein are of Wide application in the signaling art and use thereof is so intended. However, a particular use I find for the same, is in control of gating tubes in diversity receiver systems, such as for example, frequency shift or on-off" diversity telegraph systems, disclosed, for example, in Shock et al. U. S. application Serial #632,978, filed December 5, 1945.

In diversity systems of the type disclosed in said Shock et a1. application, space or propagation intercepting diversity effects are used to obtain several versions of the same signal. These versions are then compared as to quality so that the best signal may be selected for recording purposes.

A further object of my invention is to provid improved means forsensing which signal is best and improved means for controlling a locking circuit by a potential derived from the signal strength sensing means.

In a modification of the means described hereinbefore, differential control potentials are to be applied to the balanced driving tubes for the locking circuits and .a further object of my invention is to provide an improved signal sensing means for deriving differentially varying control potentials which positively flip the locking circuit to a condition of stability at which it is-to be when a certain one of the signal versions is of the greatest magnitude. It will be noted that when differential potentials areused for controlling the trigger circuit, a more positive action is obtained. i

In describing my invention, reference will be made to the attached drawings wherein: I

Figs. 1a and 11) each illustrate one embodiment of my improved trigger or looking circuit. and improved control means therefor;

Figs. 2 and 3 illustrate novel signal strength sensing means and locking circuit driving tube control means for the locking circuits illustrated in Figs. 1a and lb respectively.

In Fig. 1a, tubes 13 and M are the locking circuit tubes. The anodes of these tubes are connected by resistors H and H to the positive terminal of a direct current source, the negative terminal of which is grounded, being thereby connected through common cathode resistor K to the'cathodes of tubes I3 and I4. The anodes and control grids of tubes I3 and M are cross coupled by resistors I! and Hi. The grid direct current biasing circuits for the tubes l3 and II are completed by resistors R and R. This locking circuit as described hereinbefore operates as follows:

Assume that current is caused to start flowing in tube [3. The potential drop in the re sistor ll increases to apply a less positive or more negative potential by resistor I! to the control grid of tube M to reduce current flow in tube l4. When current flow decreases in tube I4, the potential drop in anode resistor 12 becomes less so that resistor [9 applies a more positive potential to the control grid of l3 to increase current flow in tube l3. The action is cumulative and carried to a point at which tube l3 draws full current and tube I4 is cut off. The locking circuits stay in this position until for some reason, current flow is increased in tube M or reduced in tube l3 to start a new tripping action wh ch switches the current through l4 and cuts oil current flow in tube l3.

The driver tube 9 has its anode connected to the direct current source by the resistor H and has its cathode connected directly to the cathode of a balancing tube l0. Both cathodes are connected to ground by a common resistor 45. The direct current control potential is applied to the grid I of tube 9 and for the sake of simplicity, this potential is shown as being derived from a potentiometer resistor PR; a point wh ch a be moved 1m and down to vary the potential on the grid 1. The trigger driver tube 9 drives the trigger circuit. The balancin tube In is of the same type as tube 9 and operates to eii'ect a balanced trigger circuit when the grid 1 of tube 9 has zero potential or volts applied thereto. The driver tube 9 is able to actuate the tri ger circuit because its plate is connected to the plate 01' the trigger circuit 13. and to the source through the common plate resistor II. The compensating or bal ncin tube In draws current through a resistor I 2 hich is also in the plate circuit of the tube H.

In oper tion. if trigger tube I3 is cut oil and trig er tube [4 is conduct ng. this status may be reversed by a ying posit ve potential to the gr d of tube 9. This causes tube 9 to draw more current through resistor II and drop the voltage I on the d of tu e [4, by wav of the cross couplro 'rnsistor to a oint w ere tube i4 is out off an the c rcuit fl s to the reversed status with tube l3 conducting. Actually tube I0 aids somewhat in dri ng the trigger to reverse because the pos tive potential applied to tube .9 .not on y increases the p ate current flow through resistor H. but also the cathode current flow throu 'h r si tor 5. S nce this resistor is common to both tubes 9 and H], the increased pos tive p tential across this cathode resistor tend to bias tube In to draw less current. This decrease n current through resistor 12 increases i frequency shift diversity system is illustrated in Fig. 2. In this diversity system, it is assumed that there are two receivers, one of which is designated receiver A and the other of which is designated receiver B. These receivers are excited by spaced antenna systems for diversity efiects and may comprise radio frequency amplifiers, frequency changers or converters including a detector and local oscillator and an intermediate frequency amplifier supplying output to terminals 3D and 30. The intermediate frequency output which is shifted in frequency in accordance with signals is supplied by coupling condensers 32 and 32' to the third grid electrodes in gating tubes 34 and 34. The gating tubes operate as disclosed in Schock et a1. application, Serial #632,978, filed December 5, 1945, to suppiy output from one receiver or the other to a common load ZL for use as described in said application. The gating tubes are controlled by the trigger circuit. The trigger circuit per se is as illustrated in Fig. 1a and the description thereof will not be repeated here. It will be noted that the potentials at the points X and X vary differentially as the trigger circuit is tripped between its two states of stability and that these potentials at X and X vary from say about zero potential to some negative value sufliciently high to cut oif the tubes 34 and 34' controlled thereby. The points X and X are coupled by resistors 38 and 38' to controlling electrodes in the gate tubes 34 and 34' to differentially control the operation of the gating tubes as described above.

Receiver A and recei er B o t ts are cornpared as to strength in a signal strength sensing means designated generally at 50. This means comprises transformers T and T' having band pass characteristics sufficiently wide to pass without material attenuation all of the frequency components in a frequency shift signal of intermediate frequency such as supplied at the output of receivers A and B. These transformers T and "I" each have secondary windings connected in a separate rectifier circuit including in series with the secondary winding of transformer T a rectifier diode .54, a load resistor 58 and a bypass condenser 51. The secondary winding of transformer T is similarly connected in a rectifier circuit, elements of which are designated by numerals or letters corresponding to the numerals or letters used in the preceding sentence adding prime. It will be noted that the rectifier load resistors 56 and 56' are so connected that the potential drops produced therein o pose. Thus, when the signals are of like strength, the potential at the point P should be and is substantiall zero. In this respect, note that the cathode of the rectifier 54' is grounded. This potential at P will become positive when the signal at receiver A is stronger than the signal at receiver B and will become negative when the signal at receiver A is weaker than the signal at receiver B. This will be apparent by an inspection oi. the polarities in which the rectifiers are connected to the load impedances. The'potentied at P then varies i with respect to zero potential and is supplied to the control grid 1 of the driver tube 9. If we assume that this potential swings negative which it would if the signal in receiver A is the weakest, the tube 9 would become less conductive to draw less current through resistor I and the anode potential of tube J3 would rise or become more positive as would the grid potential of tube I4. This would 75 operate as described hereinbefore to switch the current through tube 14 and make the potential at the point X more positive. This potential is applied by the resistor 38 to the controlling grid of the gate tube 34' to make this tube operative to supply signal to the load ZL and this signal is supplied from receiver B wherein the signal is the strongest. When the potential at the point P becomes positive. a second tripping action takes place as described before to switch, the current through the tube l3 to make more positive the potential at the point X and more negative the potential at the point X, to make tube 34 operative. to pass signal from receiver A and to cut ofi tube 34' to block signal from receiver B.

.The voltage peak limiting tubes 69 and. 69 and their purpose and operation in the triggering circuit have been described in Schock et a1. application. Serial #630429, filed November 23,

1945. now abandoned, and the description thereof will not be repeated herein.

The novel compensated tri gering circuit of Fig. 1b is used in the diversity receiver system of Fig. 3. The arrangement here is as described hereinbefore in connection with Fig. 1b and Fig. 2 except for the following diflerences:

The signal sensing circuit is now to provide differentially acting control potentials. one for the grid I of the driver tube 9 and the other for the grid 8 of the driver tube Ill. The signal strength sensing or comparing circuit designated generally at 50, now comprises. connected. with the secondary of transformer T, diodes 54 and 55 arranged in op osed polarity with rectifier loads 59 and GI. The secondary of transformer T is similarly connected in rectifier circuits including rectifier tubes 54' and 55' similarly connected in o posed polarity with load 59' and load 6|. The load 59 is connected in a series circuit including said load. the potential (combiner) divider incl ding resistors 19 and 12 and the rectifier load 59'. The rectifier load BI is in a series circuit with the potential (combiner) div der comprising resistors 14 and 16 and the rectifier load 6|. It will be further noted that the diodes 55 and 55' are of opposed polarity and are excited by a signal from each receiver. Their loads 59 and 59' are in series with the potential (combiner) divider including resistors 19 and 12 to provide at point P a potential which varies above say zero potential in a negative direction when the signal at the receiver A is the weakest. This potential is applied to the grid of driver tube 9. The rectifiers 54 and 54' likewise excited by energy from receivers A and B respec ively, are of opposed polarity with loads 6| and 6| in a series circuit grounded at a point between loads GI and 6! which series circuit includes resistors 14 and 16 adjacent terminals of which at point P are connected to the control grid 8 of tube ID. This rectifier arrangement is such that when the signal at the receiver A is the strongest, the potential at point P becomes more positive and the potential at point P less positive or more negative. Then the potential on the grid 8 of tube l becomes more negative to assist in switching current through tube l3 to make the potential at point X more positive and the potential at point X more negative to cut-off gating tube 34' and turn on gating tube 34 to pass the signal supplied by receiver A. When the signal from the output of receiver A is weaker than the signal from the output of receiver B, the potential at the point P becomes more negative while the potential at the point P becomes more positive to cut of!" current in the tube 13 and pass full current through the tube M to make more positive the potential at the point X to turn on tube 34' and turn off tube 34.

Normally in Fig. 3, the two transformers T and T would be identical and so would all of the diode load resistors 59, 6|, 59' and BI. Normally also resistors 10 and 12 would be identical to each other in value and may be equal to or severaltimes greater in value than the load resistors. The same may be said of resistors 14 and 16. Perhaps I may best explain the function of resistors 10 and 12 by referring to Fig. 1a. In Fig. 3 the center tapped battery of Fig. 1a may be said to have been replaced by the diode load resistors 59 and 59'. Now in Fig. 1a the two halves of the battery gave an unvarying potential supply so the potentiometer PR was used to supply voltage variations to the grid of tube 9. But in Fig. 3, where the center tapped battery is replaced by load resistors 59 and 59, there are varying potentials across these load resistors, the differential of which is applied to the grid of tube 9. So the potentiometer of Fig. 1a becomes a fixed divider in Fig. 3 embodying resistors 10 and 12 of equal value; The value of these resistors is kept high with respect to the load resistors 59 and 59 in order not to shunt these load resistors down unnecessarily.

What is claimed is:

1. In means for comparing the relative strengths of two currents which are representative of diversified versions of the same signal and for deriving potentials which vary differentially when the relative strengths of said currents vary, a first pair of rectifier systems including an alternating current path having a common portion excited by one of said currents and two direct current branch portions each including a load impedance and a rectifier device with the devices in opposed relation so that the potential drops across said loads are of opposed polarity, a second pair of rectifier systems having an alternating current path including a common portion excited by the other of said currents and two direct current branch portions each including a load impedance and a rectifier device with the last mentioned devices in opposed relation so that the potential drops across said last two load impedances are of opposed polarity, a connection between adjacent terminals of said first-mentioned load impedances and adjacent terminals of said second-mentioned load impedances, a circuit including adjacent series output impedances for adding in series the potential drops across a load impedance of said first-mentioned two load impedances and a load impedance of said secondmentioned two load impedances, a second circuit including adjacent series output impedances for adding in series the potential drops across the remaining load impedances, and means for deriving said differentially varying potentials from adjacent terminals of said output impedances.

7 of said source and the other output electrodes of the flow devices, means cross coupling the positive output electrodes and control electrodes of the flow devices so that when current starts to flow in one device, it is cut off in the other device and vice versa, a pair of control devices each having a positive output electrode coupled to the positive output electrode of a diflerent one of said locking circuit devices and each having another output electrode with a common resistor coupling the last-named output electrodes to the negative terminal of said source, each of said control devices having a control electrode, and means for applying control potentials differentially to said control device control electrodes including a first full wave rectifier circuit including series load impedances excited by signals from both of-said receivers, a connection between said load impedances and the control electrode of one control device, a second full wave rectifier circuit including series load impedances excited by signals from both of said receivers, and a connection between theload .impedances .of saidsecondrectiiler cirrcuit and the control electrode-oi the other. controldevican ROBERT. E. SCHOCK. 1

I REFERENCES CITED The following references are of record in the file of this patent: V

" UNITED' STATES PA Hollingsworth Dec. 30,

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