US1993780A - Telephone substation equipment - Google Patents

Description

March 1935. J. w. GOODERHAM El AL 1,993,780

TELEPHONE SUB-STATION EQUIPMENT Filed Feb. 11, 1951 JWGOODERHAM INVE'NTORSI H.7.BUDENBOM (.S.J HNSON I ATTORNEY Federated E2 TELEPHONE SUBSTATION EQUIPMENT John W. Gooderham, Larchmont, N. Y., and Horace T. Budenbom, Short Hills, and Kenneth S. Johnson, South Orange, N. .J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February-11, 1931, Serial No. 514,930

2 Claim.

This invention relates to telephone systems and particularly to subscribers substation equipment employed in the establishment of automatic telephone connections.

With the advent of radio broadcastingand its ever increasing popularity with the radio public there has been a demand for radio reception which is free from local controllable disturbances. It is a well known fact that the development of radio receivers has not reached the stage where they, of themselves, embody means for minimizing the objectionable effects caused by local static which is set up by neighboring electrical apparatus.

Among the types of electrical apparatus which have been found to create a condition which manifests itself in'radio receivers in the form of local static is the telephone dial. In manipulating a telephone dial to transmit impulses to prepare automatic telephone switches for the completion of a telephone connection, a current carrying circuit is interrupted intermittently a number of times in accordance with the settings of the dial.

' These interruptions eflected by the dial mechanism produce electrical surges which are picked up by neighboring radio receivers and reproduced therein as clicks or other equally objectionable noises which materially interfere with the reception of broadcast programs.

It is an object of this invention to provide an improved telephone substation set which embodies in its structure means for suppressing radio interference caused by the electrical surges set up by the manipulation of the calling dial associated with the set.

This object is attained in accordance with a feature of the invention by the provision of a filter unit which is permanently associated with the pulsing contacts of the dial associated with the subscriber's set.

Another feature of the invention resides in the small, compact design of filter which readily adapts itself to be permanently located in the base of a subscribers telephone set and in close proximity with the pulsing contacts of the calling dial. This is a particularly desirable feature in that housing the filter. unit within the base of the telephone set permits the use of smaller f lter elements with better suppression results .at the source of disturbance, than may be attained by larger elements located elsewhere at the subscribers station.

The preferred form of filter unit employed in this invention comprises two elements a condenser and an inductance coil, combined in such a manner as to form a small, compact unit which can be readily mounted on a bracket secured within the base of the telephone set and from which the necessary electrical connections with the dial contacts can-be easily made. The constants of the filter elements are necessarily predetermined to give the maximum suppression of radio interference and it has been found that the value of inductance of the filter coil is' critical within narrow limits.

Other forms of filter units which are contemplated by this invention provide various degrees of suppression and will be described in detail in a later description.

The invention will be readily understood from the following detailed description made with reference to the accompanying drawing in which Fig. 1 is a perspective view of a filter unit employed in this invention; Fig. 2 is a bottom plan view of a telephone subset with the base cover remove showing the manner in which the filter unit is-mounted within the base and its relative disposition with respect to the pulsing contacts of the dial mechanism; Fig. 3 is an elevation of a part of a telephone subset with a portion of the base casing broken away exposing the filter unit; Fig. 4 is a drawing of a substation circuit showing the manner in which the preferred form, of filter is electrically connected with the telephone dial; Fig. 5 is a drawing of a substation circuit showing a modified form of filter; Fig. 6 shows a substation circuit embodying a still further modified form of filter; and Fig. 7 shows another arrangement of applicants invention in which a two element filter located in the base of the telephone handset is employed in conjunction with an inductance coil located in the bell box.

Referring to Fig. 1, the filter elements, namely a condenser and an inductance coil may be combined and enclosed in any suitable manner in a container 10 which is provided at one end with a hook-like projection 11 which is adapted to fit into and lock in a slot in the bracket 12. The other end of the container 10 is provided with a projection 13 in which there is a hole which accommodates screw 16 by means of which the container is made fast to the bracket 12. If desirable, a resistance element may be included in the filter unit and may be incorporated in the structure of one of the leads 14 and located outside the container. Theother leads 15 are provided for obvious reasons.

The bracket 12 is secured to the underside of the casing of the subset base 17 in any suitable manner to which the container 10 of the filter unit is secured by means of screws 16 as hereinbefore described. It is believed unnecessary to identify all the apparatus disclosed in Fig. 2 as such equipment and its functions are well known to those skilled in the art. However, as the pulsing contacts -of the dial mechanism are tied up with the present invention, they are identified by the numerals 19 and 20.

In Fig. 3 a well known type of dial 21 is shown mounted on the base of a standard type telephone substation handset. By manipulating the finger wheel of the dial 21, the contacts 19 and 20 are intermittently actuated to transmit current pulses which control the setting of automatic switches in the establishment of a telephone connection.

In Fig. 4 the elements which constitute the filter unit are shown at 23 and 24 and are respectively, a condenser and an inductance coil. These two elements are connected electrically in a series circuit which is connected in shunt with the dialing contacts 19 and 20. In eflect, however, it will be noted that the inductance coil 24 is connected in series with one of the conductors of the telephone line 25. The actuation of the dial finger wheel as hereinbefore stated, causes repeated interruptions of the dialing contacts and as these contacts are connected across the telephone line 25 with which there is associated the usual current source, there are set up at the dial contacts, current surges. The filter unit consisting of the condenser 23 and inductance coil 24 acts to suppress the radio frequency components of these surges thereby rendering them ineffectire in causing disturbances to neighboring radio receivers without interference with the usual dial pulses which control the setting of automatic telephone switches.

Fig. 5 is similar to Fig. 4 except that the filter unit is shown consisting of a resistance 28, condenser 2'7 and inductance coil 22. Such a type of filter may be employed in instances where it is essential to provide protection for the contacts of the dialing mechanism.

In some cases, and particularly where the telephone is located relatively close to the radio receiver, there has been noted an increased disturbance to radio reception when the dial operator grasps the handset during dialing. In order to reduce this objectionable effect applicants have devised a modified form of filter which is shown in Fig. 6. In this arrangement, a small condenser 33 is connected at the common terminal of the filter, that is, at the point where the condenser 30 and inductance coil 31 are electrically Joined. The other side of the condenser 33 is connected to the frame of the telephone rtet as indicated by the numeral 40, Fig. 6. The insertion of a small capacity at this point has a tendency to balance out the effects caused by the body of the dial operator. condenser may be housed in the container 10 together with the other filter elements and the terminal to be secured to the frame made me- In actual practice the auxiliary weaves chanically fast to the inside of the container casing.

Fig. 7 shows a modified arrangement of the filter elements which are employed in suppressing radio interference caused by the electrical surges set up by the substation dialing mechanism. In this modification the inductance coil 35 is shown located in the bell box of the substation equipment while the condenser and resistance element 36 and 37 are shown located in close proximity with the dialing contacts, preferably within the base of the telephone handset.

The mounting of the filter unit within the base of the telephone set is a very desirable feature in that it has been determined that by so locating the filter in close proximity with the dialing contacts, the source of the disturbance, sufiicient suppression of the radio interference is obtained with considerably smaller filter elements than is obtained when the elements are located elsewhere at the subscribers station. The possibility of using relatively small filter elements in turn, renders it possible to confine the filter within a compact, unitary structure which can be readily accommodated in the very limited space available in the base of a telephone handset.

From the foregoing it is evident that applicants have not only devised a filter unit which is highly satisfactory in suppressing the interference to radio reception caused by the current surges set up by the dialing contacts of a telephone dial but by so locating the filter with respect to the dialing contacts they have rendered it possible to obtain sufficient suppression with relatively small filter elements which permit the filter unit to be made of such dimensions as to permit it to be mounted in the base of the telephone handset without relocating any of the other equipment to furnish the necessary mounting space and which may be conveniently furnished to telephone sets already in commercial use.

What is claimed is:

1. In a subscribers subset of the dial type, a filter embodied in the structure of said subset for suppressing radio interference caused by the electrical surges set up by the actuation of the dial, and a condenser electrically associated with said filter and having a terminal thereof secured to the frame of said subset for augmenting the suppression effect of said filter.

2. In combination, a telephone subset having a dial, a bracket located within the base of said telephone subset, a container housing a plurality of filter elements and having a hook-like projection at one end which fits into an aperture in said bracket and positions saidcontainer on said bracket, means for securing the other end of said container to said bracket and electrical connections between the filter terminals and the dialing contacts of said dial.

JOHN W. GOODERHAM. HORACE T. BUDENBOM. KENNETH S. JOHNSON.

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