CATV TAP

Abstract: A splitter or tap for use in a communications network, particularly a community antenna television (CATV) network comprising: an in port for receiving an incoming signal; a through port for an outgoing signal; a signal drop port; a physically removable circuit for splitting-off a first portion from the incoming signal and passing it to the signal drop port and for passing a second portion of the incoming signal from the in port to the through port; and a switch that is caused electrically to interconnect the in port and the through port on physical removal of the circuit.

Description: CATV TAP The present invention relates to a tap, or splitter, for use in a communications network, particularly in a community antenna television (CATV) network. Although various network architectures are used, they usually include a cable running from a transmitter or relay station etc., from which a signal must be tapped to subscribers. This will in general occur at several positions along a cable line. As a result a tap must receive an incoming signal, split-off part of it, and pass the rest on to the next splitter downstream. Where no signal is split-off to subscribers the device used is usually called a splitter, rather than a tap. For convenience the term "splitter" will be used herein generically. It is often necessary for power to be supplied by the network operator to the subscribers, and such power is conveniently sent along the same main cable that interconnects the splitters. The cable may therefore carry a signal that combines power, often low frequency AC, and a high frequency signal, such as a radio frequency (RF) signal. In this case, the splitter may have the additional function of splitting-off power from the incoming combined signal. We have found that designs of splitter currently available are not easily adaptable to particular field conditions or network requirements. As a result several different designs must be produced depending on the number of subscribers per splitter, on the attenuation required and on the type of power drop required etc. In order to overcome these problems we have designed a splitter that could be regarded as of modular design. Thus, the present invention provides a splitter comprising: an in port for receiving an incoming signal; a through port for an outgoing signal; a signal drop port; a physically removable circuit for splitting-off a first portion from the incoming signal and passing it to the signal drop port and for passing a second portion of the incoming signal from the in port to the through port; and a switch that is caused electrically to interconnect the in port and the through port on physical removal of the circuit. Also new and inventive is a splitter comprising: an in port for receiving an incoming signal; a through port for an outgoing signal; means for splitting-off a first portion of power from the incoming signal and for passing a second portion of the power to the through port; and a removable power distribution module that can receive said first portion of power and that has at least one power output. These various features may be combined. The invention is further illustrated by the accompanying drawings, in which: Figure 1 is a perspective view of a splitter; Figures 2A, 2B, 2C, and 2D are sections of a splitter showing an internal switch; Figures 3 A and 3B are partial perspective views of a splitter showing a power drop port; Figures 4 and 5 are perspective views of a splitter showing addition of a power distribution module; Figures 6 - 8 show sealing of cables to drop ports; Figures 9 - 1 1 show sealing of cables to main ports; Figure 12 shows sealing of blanked-off main ports; and Figures 13 and 14 show removable covers carrying splitter circuitry. Figure 1 shows a splitter 1 suitable for use in a CATV network. Splitter 1 comprises a housing 2 having various ports on its external surface for connection to various incoming and outgoing cables, and having internal electronic circuitry and - switches etc. to divide an incoming signal and/or to separate power from a high frequency component, and to provide the desired attenuation. As mentioned above, such a splitter is positioned in a CATV network at a point in a main cable line where a signal is to be split or tapped-off in order to send it to subscribers. Thus, splitter 1 has an in port (port 3 is used for an overall in-line configuration, and port 4 for an overall butt configuration) for receipt of a cable supplying a signal from a CATV transmittor etc, and a through port (port 5 or port 6 for in-line and butt configuration respectively) for connection to a cable that sends the signal (or part of it) further into the network, for example to another similar splitter. The splitter splits-off a portion of the incoming signal and supplies it to signal drop ports 7 to which are. connected drop cables to subscribers. The splitter may have, for example, 2, 4, 6, 8 or more such drop ports 7. The splitter need not be provided with the option for connecting the main cable in an in-line or butt configuration. Instead, it may have only ports 3 or 5, or only ports 4 or 6 (or one of each). Unused ports may be blanked-off as shown below. Televisions or other equipment to be supplied with a signal by splitter 1 will, in general, require an external source of power, typically at 60v AC. This power is conveniently also obtained from splitter 1 which may receive it through a main cable connected to port 3 or 4. Thus, the main cable may carry a combined power and high frequency (generally so-called RF or radio frequency) signal. The subscriber may be supplied with power through the drop cables to be connected to drop ports 7, which likewise will then carry a combined power and high frequency signal. This may, however, be inconvenient if a subscriber is not expecting 60 volts or so on his television drop cable, and we prefer that he be supplied with power through a dedicated power line. Thus, splitter 1 is provided with a dedicated power drop port 8. Some power is therefore split-off from the incoming line and sent to port 8, the remainder of the power being sent to the through port (5 or 6) for supply to the next splitter downstream. The splitter will in general contain a low pass filter to remove the high frequency signal from the drop power supply. The splitter may be provided with means such as slits 9, other recesses, or protuberances, on its ports etc. for securing environmental seals either to seal incoming cables or to locate blanking plugs. Figure 2A is a section through a splitter similar to that shown in figure 1 (taken in a plane substantially parallel to the page and viewed from behind). Figure 2B is a section taken along the arrows of figure 2A, and figures 2C and 2D are sections perpenducilar to that direction. In figures 2 A - 2D the housing 2, the in ports 3 and 4, the through ports 5 and 6 and the drop ports are visible. The ports are designed for connection to coaxial cables (although ports for other cables could be provided), and we prefer that they be sockets for receipt of cable connectors attached to cable ends, or for receipt directly of cables prepared with stepped ends. Contacts 10 for an inner conductor of a coaxial cable, and contacts 1 1 for an outer conductor can be seen. Also shown is a switch 12 comprising movable contacts 12A and 12B that, when closed, electrically connects the in port (3, 4) with the through port (5, 6). As a result, when the switch is closed, any incoming signal is directed directly from the in port to the through port without a portion of it being split-off to the drop ports. This switch 12 is however caused to be opened when the appropriate splitting circuitry is put in place. Then, the direct path between the in ports and through ports is broken, and the splitting circuitry then interconnects those ports and directs some of the signal to the drop ports 7. This circuitry is not present in figures 2A - 2D, and as a result the switch 12 is closed. The circuitry may be provided mounted on a removable cover that when in place would lie in a plane just above that of figure 2A, and as it is brought into place it would cause the contacts 12A and 12B to part. A lower metallic surface of the housing 2, for example the right-hand wall shown in figure 2B, may constitute a ground plane. We prefer that any moving parts of the switch move substantially parallel to a ground plane in order that the high frequency characteristics of the splitter do not alter as the contacts move. The switch 12 is desirable in order that service be provided downstream of the splitter when the splitter circuitry is absent; it may be desirable to remove such circuitry in order to replace it with different circuitry (for example to provide more or fewer drops, or for repair or upgrade etc.). We prefer that the act of removal of the circuitry produce no momentary break in service and therefore that physical removal of the circuit result in : 1. electrical interconnection of the in port and the through port (by the switch); and then 2. electrical disconnection of the circuit from the in and through ports. Subsequent replacement of the circuit should similarly make contact between the in and through ports (via the circuit) before breaking the direct contact by opening switch 12. In order to avoid the circuit being left partially in place (ie when connection is made between the in and through ports both through the switch and through the circuit) we prefer that the circuit pass through a position at which the interconnection (1) is made and at which the disconnection (2) has not been made, said position being unstable. Preferably a single motion (for example movement in a straight line away from the housing) causes the interconnection (1) and the disconnection (2). Also, it is preferbly the physical removal itself that causes interconnection/disconnection, rather than for example prior removal of a catch or undoing of a lock. The switch 12 is preferably mechanical, but could be an electronic switch, and it is preferably activated mechanically by direct mechanical or physical movement of the circuit or of a cover etc. to which it is attached (including some prong or other projection from the cover). Figures 2A, 2C and 2D show also means 13 such as a coil for transferring power from the in port 3 or 4 to the through port 5 or 6. Preferably means 13 acts as a low pass filter or otherwise transfers power substantially alone, i.e. without signficant high frequency, RF or other, signal that enters the in port. This will be desirable if means 13 is to act as a power split-off, or tap, for provision of power to subscribers. Power may be taken for example, at mid-point of the coil to, say, a power drop port such as port 8 of figure 1. In spite of the filtering within the body of the splitter by means 13 some further filtering may be desirable. Such further filtering may be provided within an add-on power distribution module to be described below. Figures 3 A and 3B show removal of a cover from power drop port 8. The cover may be removed by simply pulling or unscrewing, as shown in figure 3 A, or especially in the case of an integral or bonded-on cover by cutting as shown in figure 3B. Figure 4 shows the splitter with the cover removed from a power drop port 8 located on an external surface of a splitter housing 2. A gel or other internal sealing material 15 can be seen in the port 8. A power distribution module 16 is about to be connected to the splitter, electrical connection being made between, for example, inner and outer coaxial contacts 17 or 18 on the module 16 and corresponding contacts in the drop port 8. The module 16 may be physically secured to the housing by snap or interference fit catches 19A or by a bolt in a hole 19B or by other suitable means. Figure 5 shows the module 16 installed on the housing. We prefer that any removable module 16 is not itself mainly responsible for splitting-off power from an incoming power plus high frequency signal. We prefer that means for initially splitting-off power be fixed within the main housing of the splitter. Any of several function may be provided by the module. For example, the module may distribute power obtained from a single port 8 on the splitter housing to at least two power outputs 20 and/or to a different type of output from the port 8, for example to an output suitable for connection to a twisted-pair drop. Such power outputs may comprise insulation-displacement connectors or other means of securing a conductor drop. Preferably each outlet has means for connecting two conductors such as those of a twisted-pair wire 21. Each such output may be provided with a gel or other means for environmental sealing. The number of outlets will in general equal the number of drop signal ports since each subscriber will usually require its own dedicated separate power supply. A further or alternative function provided by the module 16 is filtering. The splitter itself might not be provided with a filter to remove high frequency signals from the power drop, or any such filtering might be inadequate. Module 16 may therefore provide low pass or other appropriate filtering. Electrical protection may additionally or alternatively be provided. Overcurrent or overvoltage protection devices may be used within the module to prevent current or voltage induced in or applied to any drop damaging the splitter circuitry or head end transmitting or receiving equipment, or damaging other subscribers equipment. Such devices may also protect subscriber's equipment from currents or voltages on the main lines between splitters. The devices are preferably resettable, and more preferably automatically reset. Examples of suitable overcurrent devices include those based on conductive polymers, such as those marketed by Raychem under the trademark Polyswitch. Figures 6-8 show various ways of sealing cables 22 to drop ports 7. Figure 6 shows cables 22 terminated in connectors 23 which are screwed or otherwise fixed in ports 7. The connectors 23, a portion of the cables 22 adjacent the end of the connectors, and the ports 7 are environmentally-sealed by enclosing them in sleeves 24. The sleeves 24 preferably comprise a flexible plastics material, optionally containing a gel 15 or other sealing material, and optionally having a catch 26 that engages a catch, such as slot 9, on the ports 7. The sleeves 24 may have a bellows or corrugated region to facilitate bending and/or extensibility and compressibility. A sleeve is shown before insertion on a port, together with a cap 25 that can close a cable passage therein allowing the sleeve to be used to seal an empty port. A section through a sleeve 24 is also shown to illustrate its internal structure. An alternative design of sealing sleeve is shown in figure 7. Sleeve 27 is of so-called wrap-around design and can therefore be installed around a cable 22 when it is connected to a port 7. A replacement seal can therefore be made without interrupting service to a subscriber. The sealing sleeve 27 comprises two parts hinged together at 28, and having catches to lock the ports into the closed position. A tool 30 may be provided for connecting the connector 23 to the port, particularly if the connector is short and does not protrude from the port as shown at the top right of the four ports. The wraparound sleeves 27 may snap shut and become locked over the ports by means such as 26 and 9 in a fashion that does not allow their reopening without damage. This can prevent casual tampering with the splitter to steal the signal. The sleeves of figures 6 and 7, particularly those of figure 6 may be used over a large range of cable and port sizes. Figures 8A, 8B, and 8C show how a port can be sealed without a separate external sleeve of the type shown in figures 6 and 7. A port 7 (particularly a contact 7A thereof) is accessible through a hole 32 (here defined by an upstanding cylindrical wall surrounding the screw contact 7 A) in an external surface of the splitter. The port 7 A is surrounded by a sleeve 33. When a connector 23 is screwed or otherwise attached to the port 7 A the sleeve 33 is forced into contact with edges of the hole thereby forming a seal between the connector and the external surface. Figures 9 and 10 show installation of a wraparound sealing and/or security sleeve 27 for the main cables 35 where they enter the in and through ports. The sleeve may contain a gel or other sealing material. It may in general be similar to those shown in figures 7, but larger. Figure 1 1 shows a bellows-type sleeve 24, similar to that shown in figure 6, being used on a main cable 35. Figure 12 shows a sealing cap 36, containing a gel or other sealing material, about to be placed on port 4. Also shown is a cap 36 in place. Cap 36, sleeve 24 and sleeve 27 and other devices for environmentally sealing may be provided with means for maintaining under compression any gel or other sealing material which they contain or otherwise with which they are used. It is desirable that such sealing material be maintained under compression in order that it be maintained in contact with the surfaces to be sealed. Compression may be maintained by the resilience of the caps and sleeves and/or or the housing of the splitter. Alternatively or additionally other resilient catches may be employed. The sealing material preferably comprises a gel. Preferably it comprises an oil-extended polymeric material. We prefer that it have a cone penetration value from 80 -400, especially 200 - 400, (lO^mm) (ASTM D217-68) and an ultimate elongation of at least 100% (ASTM D638-80), especially at least 200%. Other preferred properties include an ultimate tensile strength (ASTM D412) less than 1 MPa, dynamic storage modulus less than 50 KPa, and substantially zero slump up to 100°c, preferably up to 120°C. An advantage of a material such as a gel is that it can be self- sealing. As a result, an environmental seal is automatically remade on removal of a cable, connector, module or circuit board etc. Figures 13 and 14 show splitters 1 having a housing 2 and a cover 37 thereof. In figure 13 the cover carries a physically-removable circuit, components 38 of which can be seen, for splitting-off a first portion of an incoming signal entering in port 3 and passing it to signal drop ports 1, and for passing a second portion of the incoming signal to a through port (obscured in figures 13 or 14). Removal of cover 37 can be seen to open the housing and cause removal of the circuit. We prefer that removal of the splitter circuit leaves the means for power tap-off undisturbed in the housing of the splitter. In figure 13 the drop ports 7 are mounted at an opposite surface 39 of the splitter to the cover 37 such that removal and replacement of the cover breaks and makes electrical connection between the ports and the electrical circuit. Some contacts (not shown) will be provided within the splitter at each drop port and main port and at corresponding locations on the overlying electrical circuit. In figure 14 the drop ports 7 are mounted on the removable cover 39. Here connections between the drop ports and the electrical circuit can be permanent, but the design has the disadvantage that access to the inside of the splitter, or exchange of the cover plus circuitry, requires the drop ports to be disturbed.

Claims: CLAIMS 1. A splitter comprising: an in port for receiving an incoming signal; a thrpugh port for an outgoing signal; a signal drop port; a physically removable circuit for splitting-off a first portion from the incoming signal and passing it to the signal drop port and for passing a second portion of the incoming signal from the in port to the through port; and a switch that is caused electrically to interconnect the in port and the through port on physical removal of the circuit. 2. A splitter according to claim 1, in which physical removal of the circuit results in: 1. electrical interconnection of the in port and the through port; and then 2. electrical disconnection of the circuit from the in and through ports. 3. A splitter according to claim 1 or 2, in which physical removal itself of the circuit causes the interconnection (1) and the disconnection (2) 4. A splitter according to claim 3, in which a single motion of the circuit causes the interconnection (1) and the disconnection (2). 5. A splitter according to claim 3 or 4, in which on removal the circuit passes through a position at which the interconnection (1) is made and at which the disconnection (2) has not been made, said position being unstable. 6. A splitter according to any preceding claim, in which the circuit is mounted on a removable cover that constitutes part of a housing such that opening of the housing causes said removal of the circuit. 7. A splitter according to claim, 6, in which the drop port is mounted on the removable cover. 8. A splitter according to claim 6, in which the drop port is mounted at an opposite surface thereof to the cover such that removal and replacement of the cover breaks and makes electrical connection between the port and the electrical circuit. 9. A splitter according to any preceding claim, having at least two of said signal drop ports. 10. A splitter according to any preceding claim which has a ground plane, and in moving parts of said switch move substantially parallel to the ground plane. 11. A splitter according to any preceding claim, having means for splitting-off a first portion of power from a combined power and high frequency signal at the in-port and for passing a second portion of the power to the through port. 12. A splitter according to claim 11, in which said means is physically separate from said removable circuit. 13. A splitter according to claim 1 1 or 12, in which said means is substantially incapable of transmitting said high frequency signal. 14. A splitter according to any of claims 11, 12 and 13, in which the first portion of power is passed to a dedicated power drop port. 15. A splitter according to claim 14, in which the first portion of power is passed to a plurality of dedicated power drop ports; the splitter having a plurality of signal drop ports equal in number to the number of dedicated power drop ports. 16. A splitter according to claims 14 or 15, which additionally comprises a removable power distribution module that receives power from the dedicated power drop ports and that has a plurality of power outputs. 17. A splitter according to any of claims 14 - 16, in which the or each dedicated power drop port comprises an insulation displacement connector. SUBSTITUTE SHEET (RULE 2b) 18. A splitter according to claim 16, in which the power distribution module has overcurrent and/or over voltage protection. 19. A splitter according to claim 16, in which the power distribution module includes a low pass filter. 20. A splitter according to any preceding claim having a port environmentally sealed by a seal comprising a gel. 21. A splitter according to any preceding claim, having a port to which a cable can be attached, the port being accessible through a hole in an external surface of the splitter and being surrounded by a sleeve, such that when the connector is attached to the port the sleeve is forced into contact with an edge of the hole thereby forming a seal between the connector and the external surface.

Inventors: KOHLHAAS MARTIN, PINYAN JAMES ALEXANDER, TOURNEL WILLY, KOHLHAAS, MARTIN, PINYAN, JAMES, ALEXANDER, TOURNEL, WILLY
Applicants: KOHLHAAS MARTIN, PINYAN JAMES ALEXANDER, RAYCHEM LTD, ROSE WALTER GMBH & CO KG, TOURNEL WILLY, KOHLHAAS, MARTIN, PINYAN, JAMES, ALEXANDER, RAYCHEM LIMITED, TOURNEL, WILLY, WALTER ROSE GMBH & CO. KG
Application year: 1995
Main classification: H01R17
IPC codes: H01R13, H03H7, H04N5, H04N7