Catv Multi-tap Distribution Box

Abstract

A Multi-Tap distribution box for a community antenna television system, the box being interposed in a primary line-carrying radio and video signals from a master station to subscribers who are linked to the primary line by secondary lines coupled to the taps on the box. The box consists of an open housing having input and output ports interconnected through a normally-closed switch whereby signals pass through said housing. Removably secured to the housing is a tap plate having a distribution network mounted on its inner face, the network being connected to a group of taps projecting from the outer face, means being provided to connect the network to the input and output ports. The plate further includes means to engage and break open the switch whereby the distribution network is rendered operative to supply the signals to the taps.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to multi-tap distribution boxes for a community antenna television system, and more particularly to an improved box for this purpose.

In a community antenna television system (CATV), a primary line in the form of a coaxial cable serves to conduct television and radio signals from a master station for distribution to the homes, offices, and other facilities of subscribers in the community being serviced. Distribution boxes are installed at various points along the cable. These boxes in some instances are placed in outdoor or underground lines, or they may be installed in the basement of an apartment house, in which event they are more readily accessible. Drop lines taken from the taps on the distribution boxes serve to carry the signals to the subscribers' television sets. The primary line also functions to conduct power to the various signal amplifiers included in the system to maintain the signal at the proper level. Since the video and radio signals are in the high-frequency range, they will hereafter be referred to as R-F signals, as distinguished from low-frequency A-C power for energizing a signal amplifier.

The standard, sealed multi-tap distribution box, often referred to as an SMT box, is constituted by a housing having an open well and a removable tap plate which seals the housing, the tap plate being provided with a circuit board that is accommodated within the well.

Disposed in the well of the housing is a blocking inductor whose ends are connected to roll pins extending from coaxial input and output ports at the opposite ends of the housing. When installed, the box is interposed in the primary CATV line through the input and output ports therof. The inductor interconnecting the ports offers a high impedance to the passage of R-F signals between the upstream and downstream side of the line, but it presents no significant impedance to low-frequency A-C power currents carried by the line to energize the line amplifiers. Thus the blocking inductor acts to block only R-F signals, not the flow of power.

The circuit board is provided with connecting clips which when the board is in place within the housing well, are adapted to engage the roll pins. These clips or connectors are connected on the circuit board to a distribution circuit which includes a series network that shunts the inductor and transfers the R-F signals between the input and output ports, and a tapping network connected to the series network for directing a portion of the signal to a set of external taps on the tap plate.

When therefore the tap plate is properly secured to the housing, R-F signals on the primary line are distributed to the set of taps, the signals at the same time being conducted downstream to other SMT boxes and amplifiers on the downstream side of the primary line. But when the tap plate is removed during periods of maintenance or subscriber hookup, the R-F signals are interrupted and there is a loss of signal in the downstream boxes and amplifiers.

The use of standard SMT boxes such as the box disclosed in U.S. Pat. No. 3,675,181 has a number of disadvantages, for the loss of R-F signal which results when a tap plate is removed, cuts off signal reception at the downstream distribution points. Moreover because the blocking inductors in all of the standard SMT boxes are identical and have the same characteristics, the value thereof may not be optimum for all taps. In order to achieve optimum return loss and isolation, it is desirable that the value of the blocking inductor be tailored to individual tap value designs rather than have a single value which represents a compromise in the range of preferred or optimum values.

But the greatest practical objection to existing types of CATV multi-tap boxes is economic, for such boxes add substantially to the cost of constructing a dedicated CATV system. A dedicated CATV system is one in which the multi-tap boxes are made a part of the system at the time of construction. The number and spacing of the boxes on the primary line are determined by taking into account the existing demand for services and the projected future need therefor. Thus the usual dedicated system is designed to provide taps for all current and potential subscribers, or a projection of 100 percent saturation. As a consequence the owner of a dedicated CATV system in a sense must also dedicate his construction costs, for the owner is required to make an initial investment to take care of potential subscribers, some of whom may never enlist.

The reason why a dedicated CATV system is preferred over prior methods of construction, despite their high initial costs, is that the system affords signals of better quality and permits the addition of new subscribers without disturbing those already tapped into the cable. Nevertheless the technical advantages are in large measure offset by economic drawbacks.

SUMMARY OF THE INVENTION

In view of the foregoing, it is the main object of this invention to provide a CATV multi-tap signal distribution box whose housing contains only those elements necessary for signal and power integrity and whose removable tap plate includes only those elements essential to signal distribution.

A salient feature of the invention is that for purposes of constructing a dedicated CATV system, the owner need only install the relatively inexpensive housings in the primary line, for these housings are adapted to convey both signal and power. The more costly tap plate need be purchased and installed by the owner of the system only when required to add paying subscribers to the system.

Thus the initial construction cost of a dedicated system including multi-tap boxes in accordance with the invention, is far below existing costs, without any loss in the technical advantages gained by the system.

More particularly, it is an object of the invention to provide an SMT distribution box for a dedicated CATV system which box includes a housing and a removable tap plate, the housing being adapted to convey R-F signals between the input and output ports thereof in the absence of the tap plate as well as when the tap plate is secured to the housing.

Also an object of the invention is to provide an SMT box of the above-type which includes a signal blocking inductor that is interposed between the input and output ports thereof only when the tap plate is in place on the housing (closed-box state), in which state the inductor is shunted by a series network to transfer R-F signals between the ports, the input port being directly connected to the output port when the tap plate is withdrawn from the housing (open-box state) whereby R-F line signals are conveyed between the upstream and downstream side of the line in both states.

Among the significant advantages of the invention are that the blocking inductor is mounted on the circuit board of the tap plate and has a value which is optimum for the distribution circuit, and that R-F signals and power currents are not interrupted in the open-box state, thereby improving customer relations in that the system is maintained in operation at all times.

Yet another object of the invention is to provide an SMT box which is capable of in-line or right-angle mounting, and which operates efficiently and reliably.

Briefly stated these objects are attained in a multi-tap signal distribution box formed by a housing which is provided with a normally-closed switch which interconnects the input to the output port to conduct both power and signal. Removably secured to the housing is a tap plate having means to engage and open the switch, the plate being provided with a distribution circuit which is coupled to said ports and is rendered operative when said switch is open, to supply said signal to a group of taps.

In a preferred embodiment of the box, the housing is provided with an open well within which is disposed a normally-closed switch constituted by a fixed contact in the form of a rigid pin extending from one of the coaxial ports and a movable contact in the form of a flexible pin extending from the other port, the free end of the flexible pin having a contact element thereon which normally engages the free end of the rigid pin.

Cooperating with the housing is a tap plate having mounted on the underface thereof a circuit board which is received within the well, and which has on the outerface thereof a set of distribution taps, the circuit board being provided with a pair of contact clips adapted to engage the rigid and the flexible pins as well as a pusher member which engages and deflects the flexible pin to break its connection to the fixed pin, thereby opening the switch. A blocking inductor mounted on the circuit board is connected between the clips and hence between the input and output ports, the inductor being shunted on the board by a series network which conveys the signal between the ports and also supplies the signal to a distribution network leading to the taps.

Thus in the open state when the tap plate is removed from the housing, the switch in the well is closed to maintain an R-F and power connection between the ports, while in the closed state, the switch is open to maintain an R-F signal connection between the ports through the series network and a power connection between the ports through the inductor.

OUTLINE OF DRAWING

For a better understanding of the invention as well as other objects and features thereof, reference is made to the following detailed description to be used in conjunction with the annexed drawing, wherein:

FIG. 1 is a schematic circuit of a standard SMT distribution box;

FIG. 2 is a schematic circuit of an SMT distribution box in accordance with the present invention;

FIG. 3 is a perspective view of an SMT distribution box in accordance with the invention;

FIG. 4 is a longitudinal section taken through FIG. 3;

FIG. 5 is a plan view of the housing of the box;

FIG. 6 is a plan view of the underside of the tap plate for the box, showing the circuit board;

FIG. 7 is a perspective view showing only the well switch and the connectors and pusher member cooperating therewith.

FIG. 8 is a perspective view of one of the seizing elements, and

FIG. 9 is a plan view of the box with a blank plate mounted thereon.

DESCRIPTION OF INVENTION

Prior Art Box

Referring now to FIG. 1, there is shown the schematic diagram of a prior art type multi-tap distribution box formed by a housing 10H and tap plate 10T associated therewith. The box is interposed in a primary line 11 or coaxial cable of a CATV system, the housing having an input port 12 and an output port 13 for connection to the cable. The section of the primary line connected to the input port is on the upstream side and that connected to the output port is the downstream side. The tap plate is provided with a set of external taps 1, 2, 3 and 4 which are connectable to subscribers by means of secondary or drop lines provided with suitable couplers. In practice, a greater or smaller number of taps may be provided to meet system requirements.

Disposed within an open well in housing 10H is a blocking inductor 14 whose ends are connected to the free ends of axially-aligned rigid roll pins 15 and 16 extending from input port 12 and output port 13, respectively. The blocking inductor presents a high impedance to R-F signals carried by the primary line and serves therefore to block the passage of these signals without impeding the flow of low-frequency A-C power.

Tap plate 10T is provided with a circuit board that fits into the housing well containing the blocking inductor. Mounted on the circuit board are connectors 17 and 18 which when the circuit board is inserted in the well, engage rigid pins 15 and 16. Connected between connectors 17 and 18 is a series network formed by capacitor 19, the first primary coil 20 of a directional coupler 21 and a capacitor 22. The parameters of this series network are such as to afford a relatively low-impedance R-F path which by-passes the high impedance blocking inductor to convey the R-F signals from the upstream input port to the downstream output port. Thus when the tap plate is secured to the housing, blocking inductor 14 is by-passed by the series netowrk to convey R-F signals down the primary line to other SMT boxes and amplifiers in the CATV system.

Directional coupler 21 acts to divert signals from the series network to the taps leading to the subscribers' T-V sets, while preventing signals originating at these sets, such as the local oscillator signal, from being transferred to the primary line, for such local signals if conveyed on the primary line will produce interference. The coupler includes two phased transformers, the primary 20 of the first transformer being included in the series network and the secondary 23 thereof being connected at one end to ground through a signal-splitting coil 27. The primary 25 of the second transformer of the directional coupler is connected between the other end of secondary 23 of the first transformer and the junctions of capacitor 19 and the primary 20. The secondary 26 of the second transformer is connected between ground and the junction of secondary 23 and coil 27.

Signal-splitting coil 27 of the distribution network is connected at its center tap to a circuit tree composed of coils 28, 29 and 30 leading to taps 1, 2, 3 and 4. It is to be understood that the distribution circuit shown is merely illustrative and that other known circuit configurations have been used in connection with the taps.

The New Box

In the prior art SMT box arrangement shown in FIG. 1, the connectors 17 and 18 are disengaged from pins 15 and 16 when tap plate 10T is withdrawn from housing 10H, causing an interruption in the flow of R-F signals between the upstream and downstream side of the primary line.

An arrangement in accordance with the invention is shown schematically in FIG. 2 where in place of a blocking inductor, the housing 10H of the box is provided with a normally-closed switch constituted by a fixed contact FC formed by a rigid wire or pin extending from the input port 12 and a movable contact MC formed by a flexible wire or pin extending from output port 13. In the absence of a deflecting force, the two contact pins are normally in axial alignment, flexible pin MC having a latching contact element CE secured to the free end thereof which engages the free end of the fixed pin FC to close the switch.

Thus the switch FC-MC interconnecting the input and output ports in the box housing is normally closed to pass both the RF signals and the power currents on the primary line. The tap plate in this instance includes not only the connecting clips 17 and 18 which engage pins FC and MC when the tap plate 10T is secured to the housing, but a pusher element PE which engages and raises or deflects flexible pin MC to break open the switch.

Mounted on the circuit board of the tap plate is the blocking inductor 14, the ends of the inductor being permanently connected to connectors 17 and 18 whereby this inductor is connected between the input and output ports only when the tap plate is secured to the housing. Hence in the present invention, the blocking inductor forms a part of the circuit on the tap plate circuit board and may be tailored so that its value is optimum for that particular distribution circuit.

Shunted across inductor 14 is the series network formed by capacitor 19, primary 20 and capacitor 22, the series network serving to transfer R-F signals between the input and output ports as well as to supply a portion of this signal to the distribution network leading to the taps, in the same manner described in connection with FIG. 1.

Thus in the box arrangement shown in FIG. 2, in the open state of the box the switch therein is closed to conduct R-F signals and power currents and thereby maintain a direct connection between the upstream and downstream sides of the primary line, in contradistinction to the prior art arrangement shown in FIG. 1 wherein R-F signal transmission is interrupted in the open-box state.

In the closed-box state (FIG. 2) the switch is held open and power currents are transmitted through the blocking inductor while R-F signals are transmitted through the series network shunting the inductor, this being true also in the prior art arrangement.

Referring now to FIGS. 3 to 6, the actual structure of an SMT distribution box in accordance with the invention is illustrated. The tap plate 10T is secured to the housing by four captive screws S.sub.1, S.sub.2, S.sub.3 and S.sub.4 (FIG. 9). The contact pins FC and MC extend from seizing elements 31 and 31' which are received in ports 12 and 13. Each seizing element, as shown in FIG. 8, includes an axial inlet A.sub.1 and a lateral inlet A.sub.2 whereby the primary line coupling to the box may be axial or at right angles thereto.

The circuit board 32 which is mounted on the underside of tap plate 10P carries the circuit components illustrated in FIG. 2 as well as connecting clips or connectors 17 and 18 and pusher member PE.

When the tap plate 10T is installed on housing 10H, the circuit board is received within the open well 33 formed in the housing, the pusher member PE engaging and deflecting the movable contact MC to break the switch. At the same time, the connecting clips 17 and 18 engage the switch contacts to introduce the circuit between the input and output ports (FIG. 7).

Thus the owner of a dedicated CATV system even before he has enlisted subscribers at various points along the line, may install at these points only the housings of SMT boxes but without tap plates, the installed housings containing the closed switches which maintain signal and power integrity. When subscribers are available at a given point, the owner can then purchase and install a tap plate on the housing. Thus the owner need not go through the expense of buying tap plates until this expense is warranted. In order to seal off housings before tap plates are installed, a blank cover 34 such as that shown in FIG. 9, may be used to seal the housing and protect the switch therein.

While there has been shown a preferred embodiment of the invention, it will be appreciated that many changes may be made therein without departing from the essential operation thereof. Thus the invention is not limited to the particular form of switch shown in the housing, and other types of switches may be used to intercouple the input and output parts.

Claims

I claim:

1. A multi-tap distribution box for a community antenna system, said box being interposed in a primary line carrying high-frequency signals and power currents to subscribers who are linked to the primary line by secondary lines coupled to taps on the box, said box comprising:

A. an open housing having an input port and an output port for interposing the box in the primary line.

B. a switch disposed in said open housing, said switch having a fixed element connected to one of said ports and a movable element connected to the other of said ports,

C. a removable tap plate secured to said housing to seal same, said plate having external taps and being provided with a circuit board on which is mounted a pair of connectors adapted to engage the elements of said switch, means deflecting said movable element to break open said switch, a blocking inductor connected between said connectors to provide a passage between said ports for said power currents while impeding the flow of said high-frequency signals therebetween, a by-pass network shunted across said inductor to provide a passage for said high-frequency signals, and a distribution network connected to said by-pass network to supply a portion of said signals to said taps whereby when said tap plate is removed from said housing, said switch closes to convey both said signals and said power currents between said ports and when said tap plate is secured to said housing, said switch opens and said signals are conducted by said by-pass network and said power currents are conducted by said inductor.

2. A box as set forth in claim 1, wherein said housing includes an open well which contains said switch, said circuit board being received within said well.

3. A box as set forth in claim 1, wherein said distribution network is coupled to said by-pass network by a directional coupler.

4. A box as set forth in claim 1, wherein said primary line is a coaxial cable and said ports have an axial inlet and a lateral inlet whereby said cable may be axially coupled to said port or at right angles thereto.

5. A box as set forth in claim 4, wherein each port is provided with a seizing element having said inlets and anchoring said switch elements.

6. A box as set forth in claim 5, wherein said fixed element of the switch is a rigid pin and said movable element is a flexible pin.

7. A box as set forth in claim 6, wherein said means to deflect said movable element is a pusher member mounted on said circuit board.

8. A multi-tap distribution box for a community antenna system, said box being interposable in a primary line carrying high-frequency signals and power currents to subscribers who are linked to the primary line by secondary lines coupled to taps on the box, said box comprising:

A. a housing having an input port and an output port for interposing said box in the primary line and a normally-closed switch disposed in said housing to interconnect said ports, and

B. a tap plate removably secured to said housing, said tap plate having a group of external taps, means engaging said switch to break open same, a distribution network coupled between said ports when said plate is secured to said housing to supply said signals to said taps, said network being rendered operative only when said switch is open.