US2078974A

US2078974A - Modulating system

Info

Publication number: US2078974A
Application number: US89363A
Authority: US
Inventors: Robert R Riesz
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1936-07-07
Filing date: 1936-07-07
Publication date: 1937-05-04
Anticipated expiration: 1954-05-04
Also published as: NL44525C; FR824728A; GB478994A

Description

May 4, 1937.

FIG.

R. R. RlESZ MODULATING SYSTEM Filed July 7, 1956 BPF. gm

BPF

UM/$44 M TTORNEV ing a Wheatstone-bridge network lll which is Patented May 4, 1937 Q umrlzn anew 2,078,974 MODULATING SYSTEM Robert RaRiesz, Mount Vernon, N. Y., assignor to BellTelephoneLaboratorics, Incorporated, New

York, N. Y., acorporation of New York ApplicationJulyfl; 1936, Serial No. 89,363

This invention relates to modulating systems, and moreparticularl-yto modulating systems employing physically inert non-linear; resistance applying a signaling voltage across the points 2| elements as-modulatingapparatus;

an; object of the inventionls to; obtain incircuitlof a modulatingsystem;'

creased suppression of the an'ier in the output In apreferred-embodiment;theinvention coma prises plurality "of physically inert'-'non-'linear.'

resistance elements arrangediin the form of a Wheatstone bridge in l l a" modulating, system to effect: signal 'modulation of carrier waves. relatively small"resistance connected in series in one carrier conductive arm and arelatively large in the output circuit.

Theinvention'will'be more fully comprehended from the. following description taken together with the accompanying drawing in "which:

Fig; 1 illustrates a preferred embodiment of the invention; and

Fig. 1A shows one'modification' of-the invention;

Figs. 13, 1C and 1D illustrate-other modifications of the invention.

Fig. 1 illustrates a modulatingsystem-embody connectedin shunt with filters ll 'and l2f The filter I l adapted to pass a band of modulating frequencies produced-at'a signaling source I3 is directly connected to the output filter l2. A load M is connected across the output filter 12 which is adapted to pass side-band frequencies lying adjacent to the carrier vfrequency produced by a generator l5. Leads l9 and 20 connecting filters l l and 12 are also joined to points 2i and 22 of the bridge network l0 whose

points

24 and 25 are connected to filter 23 associated with the carrier generator l5.

The Wheatstone bridge network It! comprises physically inert

non-linear resistance elements

29, 30, 3| and 32. These may be of any suitable non-linear type, such, for example, as copperoxide rectifiers or other non-linear resistors of suitable type. The rectifiers are poled as indicated by the arrows in Fig. 1, such that

nonlinear resistance elements

29 and 30 are poled in a carrier non-conductive direction toward common terminal 24 while non-linear resistance elements 3| and 32 are poled in a carrier conductive direction away from common terminal 25.

Theoperation of. the W'heatstone bridge in a modulating system is well-known and consists in voltages together with the non-linear resistanceelements produce a modulation actionzwhereby the carrier-;cur-rents and signaling currents are combined in the well-known manner to effect a signal modulation of thecarrier Wave of the carrier suppressed type. This is most efficiently accomplished, when the non-linear resistance elements comprising the bridge network.- barebalanced to a high degree of precision in both the conductive and non-conductive directions with respect to carrier.

In a preferred embodiment, the invention comprises a variable resistance 33 connected in series with the non-linear resistance element 3| of'a conductive arm and a variable resistance 34 connected in shunt with the non-linear resistance element 32 ofa non-conductive arm, the terms conductive and-non-conductive being used with reference toi the carrier wave.

By a use of= theseresistances an accurate balancemfthe bridge network. in in the conductive and non-conductive directions may be obtained J as follows.-

ance 3|. is varied to producethe best. bridgebalance ,forthe conductive direction, Also, with no signalcurrent but with the carrier current flowing in the non-conductive direction, resistance 34 is varied to effect the most accurate bridge balance for the non-conductive direction. Accordingly, by alternate adjustments of the

resistances

33 and 34, the bridge network ll! may be eventually balanced to a high degree of precision. Obviously, a precise balance is desirable so as to obtain maximum suppression of carrier waves in the output circuit.

It will be noted, however, that resistance 33 is effective in only one arm in the conductive direction and one arm in the non-conductive direction, and further, that shunt resistance 34 is effective in connection with but one arm of the non-conductive direction. Inasmuch as resistance 33 has a relatively low value of the order of 5 ohms, it will not appreciably affect the balance in the non-conductive direction. Likewise, since resistance 34 has a relatively large value of the order of 5500 ohms, it will not appreciably influence the balance in the conductive direction.

It will be understood that the same result is also attained when the resistance 33 is connected in series with either resistance element 3| or 32 and the resistance 34 in shunt with either the resistance element 3| or 32. Bridge circuits embodying these modifications are shown in Figs. 13, 1C and 1D.

The connection of the series resistance 33 and shunt resistance 34 in the above combinations depends on the conducting and non-conducting resistance values of the non-linear resistance elements. The respective resistance values may be indicated as follows: In balancing a Wheatstone bridge, it is essential that Then in the conducting direction,

- 322 If 30 3l resistance 33 is inserted in series with resistance element 3|; and 29 53 if ao 3i resistance 33 is placed in series with resistance element 32.

Similarly, in the non-conducting direction,

resistance 34 is connected in shunt with resistance element 32; and 522 E If ao R31 resistance 34 is connected in shunt with resistance element 3|.

Fig. 1A illustrates a modified Wheatstone bridge network 35 that may be substituted for the bridge network ID of Fig. 1. In Fig. 1A, a potentiometer 36 is interposed between the non-linear resistance elements 3| and 32 poled in the conductive direction away from contact point 25. By this arrangement, the conductive arms containing resistances 3| and 32 may be varied simultaneously. Further, it is seen that the potentiometer 36 is effective in both non-conductive arms as well as both conductive arms. The potentiometer 36 has a relatively small resistance; therefore it will not appreciably afiect the balance in the non-conductive direction. Likewise, the resistance 34 is relatively large, hence it will not appreciably afiect the balance in the conductive direction.

In Fig. 1A, the resistance 34 may be connected in shunt with either resistance element 3| or 32 depending on the non-conducting resistance values of the non-linear resistance elements as illustrated above relative to Fig. 1.

It will be understood, of course, that the bridge networks l0 and 35 may be balanced to a high degree of accuracy in a minimum of time when the four non-linear resistance elements are substantially identical.

What is claimed is:

1. A modulating system of the carrier suppressed type comprising a source of modulating Waves connected in an input circuit of the system, an output circuit, a balanced Wheatstone bridge comprising a physically inert non-linear resistance element in each of its arms, the Wheatstone bridge being interposed between the input and output circuits, a source of carrier Waves connected to the Wheatstone bridge for modulation therein by said modulating waves, and means for increasing the degree of suppression of the unmodulated carrier component by providing a more accurate bridge balance than is afiorded by balancing said non-linearresistance elements against one another comprising a resistance connected in series with a non-linear element in one arm of the bridge and a resistance connected in shunt relation to the non-linear element in a different arm of the bridge, said series and shunt resistances being proportioned to provide the required degree of balance.

2. A modulating system according to claim 1 in which the series resistance has such a value as will unappreciably affect the bridge balance in the non-conductive direction while the shunt resistance has a value that will unappreciably affect the bridge balance in the non-conductive direction while the shunt resistance has a value that will unappreciably affect the bridge balance in the conductive direction.

3. A modulating system according to claim 1 in which the resistance connected in series in an arm is in series with one of the non-linear resistance elements poled in a conductive direction away from a common terminal.

4. A modulating system according to claim 1 in which the resistance connected in series is a potentiometer interposed between the two nonlinear resistance elements poled in the conductive direction away from a common terminal.

ROBERT R. RIESZ.