Abstract:
A multiple cavity, multiple port modular CATV housing permits a plurality of taps, splitters, equalizers and amplifiers to be arranged in various combinations. A plurality of modular cavities is connected in series from a coaxial connector input. Each modular cavity contains a module switch, which provides conductivity between the input and output of each respective modular cavity when the modular cavity is empty, and opened when a plug in module is inserted into the modular cavity. Various flexible electrical and mechanical modular configurations of CATV components are configured by plugging or unplugging desired modules such as subscriber taps of various numbers and values, an amplifier, an equalizer, a terminating load or a mid-module output. Taps with different values may be used in different modular cavities to accommodate longer subscriber drop lines.

Description:
FIELD OF THE INVENTION 
     The present invention relates to CATV distribution equipment, and in particular the present invention relates to a multiple port housing for providing flexible electrical and mechanical modular configurations of CATV components such as taps, splitters, equalizers and amplifiers. 
     BACKGROUND OF THE INVENTION 
     A cable television (CATV) system distributes a broadband RF signal to individual subscriber locations. The headend originates the RF signal, and the distribution network divides, or distributes, the signal to each subscriber location. Amplifiers and line extenders carry the RF signal to a local distribution point near a group of subscriber locations. A tap is used to “tap” some of the RF signal from the local distribution point and deliver it to the subscriber&#39;s home via a coaxial drop cable. Typically, a tap is a 2, 4, or 8 port device, which respectively provides service to 2, 4, or 8 subscriber locations. 
     Taps vary in both the numbers of subscriber output ports and the level of RF signal (the tap value) that is tapped from the input RF signal. Tap values are expressed in dB of attenuation from the input RF signal. Most taps divert only a portion of the input RF signal to subscriber output ports and pass almost all of the input signal level to the output connector. A directional coupler is not linear in tap value to insertion loss correlation (insertion loss is the signal attenuation from input to output) the higher the tap value the less insertion loss in the directional coupler. A 20 dB directional coupler will only have about 0.8 dB of insertion loss where as a 9 dB directional coupler will have about 2.5 dB of insertion loss Some taps are terminating taps that have subscriber output ports but no output connector. 
     A typical tap has a directional coupler and an internal splitter network. The directional coupler taps a fixed level of RF signal from the input connector, and passes the tapped RF signal through the internal splitter network. The subscriber output ports are connected to the splitter outputs. The output of the directional coupler is connected to the tap output connector, which couples input RF signal less the directional couplers insertion loss to the next tap in the CATV system. A terminating tap (which has no output connector) includes only a splitter network and subscriber output ports for connection to local subscriber drop lines. 
     In very dense subscriber locations, it is known to cascade several 2, 4 or 8 port taps together in one location to serve 24, 32 or even 48 homes. In such case, each tap is selected for a desired value and required number of ports. The same tap housing accommodates any one of a variety of possible tap variations. That is, a typical tap housing is designed to hold any one of a number of different tap configurations, and a given line of taps will fit the common tap housing design. To increase the number of subscriber ports at a given location, additional tap housings are added in series. 
     However, in order to add additional tap housings in series, the downstream side of the CATV system is disconnected, which interrupts service to the downstream subscribers. In addition, as more subscribers are added, amplification and/or equalization of the RF signal may become necessary to avoid loss of quality of the RF signal. Installing an amplifier or equalizer will interrupt service to downstream subscribers. As CATV services upgrade to include advanced services such as telephone or Internet access, even brief interruptions in service is unacceptable. 
     In areas with a large number of subscribers, it is also known to use large multi-port, multi-value tap configurations that incorporate fixed cascades of 4 and 8 port taps with different tap values in a single housing. Multiple large tap product versions include 16, 32, and 48 port models with bandwidths ranging form 5 MHz to 1000 MHz. Different tap values in one large tap housing permit the use of different lengths of subscriber drop lines while still providing proper signal levels to the television sets. 
     The advantage of a large multi-port, multi-value tap housing as compared to cascading separate 8-port taps, is that large tap configurations are less expensive, are specifically designed for the application (which enhances the RF performance) and require less space. However, the number of possible large tap variations leads to a large number of product models. Also, during field service, if one of the internal taps or subscriber ports is found to be damaged or defective, the whole multi-port, multi-value large tap may have be replaced. 
     SUMMARY OF THE INVENTION 
     The present invention is embodied in a multiple cavity multiple port modular CATV housing in which a plurality of taps, splitters, equalizers and amplifiers may be arranged in various combinations. At least a first coaxial connector is provided, with a plurality of modular cavities connected in series from said first coaxial connector. In a second embodiment, first and second coaxial connectors are provided with a plurality of ports connected in series from said first coaxial connector to said second coaxial connector. 
     Each modular cavity contains a module switch, which provides conductivity between the input and output of each respective modular cavity. In particular, the module switch is closed when the modular cavity is empty, and opened when a module is inserted into the modular cavity. Since the module switch is shorted when the modular cavity is empty, the CATV distribution network is configured by plugging or unplugging desired modules. In addition to subscriber taps (tap modules) of various values and with various numbers of subscriber ports, a plug in module may be an amplifier, an equalizer, a terminating load or a mid-module output. Blank modules may be either the shorting type (not operating the module switch) or non-shorting type (operating the module switch). 
     The present invented housing accommodates various flexible electrical and mechanical modular configurations of CATV components, both for initial CATV distribution system designs and subsequent reconfigurations in the field. For example, an installation may start with very few subscribers and later be expanded to additional subscribers by installing additional 2, 4 or 8 port subscriber taps without disrupting service to the existing subscribers. For new subscribers with longer drop lines, subscriber taps with smaller values may be plugged into an available modular port. 
     If the RF signal becomes too attenuated or sloped to supply more taps, a modular cavity may be used to insert an amplifier or equalizer into the series connection. Terminating taps or modules may be installed in any modular cavity and moved at will to make room for additional intervening taps. The modular housing may further be used for series connection beginning at either end or from both ends simultaneously. 
     The multiple cavity, multiple port modular CATV housing permits replacement of defective or damaged taps without replacing the whole tap. The installer may revalue a tap by installing a module with different tap values as the design parameters of the cable system change. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view drawing of a multiple cavity, multiple port modular CATV housing in accordance with the present invention. 
     FIG. 2 is a perspective exploded view drawing of a multiple cavity, multiple port modular CATV housing in accordance with the present invention. 
     FIG. 3 is a detail cross-sectional assembly drawing of two modular cavities with corresponding module switches and plug in subscriber tap modules in accordance with the present invention. 
     FIG. 4 is a cross-sectional assembly drawing of a multiple cavity, multiple port modular CATV housing including a plurality of modular cavities, module switches and plug in subscriber tap modules in accordance with the present invention. 
     FIG. 5 is a top transparent view of a multiple cavity, multiple port modular CATV housing embodying the present invention. 
     FIG. 6 is a schematic diagram of a multiple port modular CATV housing in accordance with the present invention. 
     FIG. 7 is a detail view of a module switch for use in a multiple cavity, multiple port modular CATV housing in accordance with the present invention. 
     FIGS. 8-14 illustrate various combinations of plug in modules including terminating and non-terminating subscriber taps, blank modules, amplifier modules and equalizer modules for use in conjunction with the present invention. 
    
    
     DETAILED DESCRIPTION 
     A multiple cavity, multiple port modular CATV housing  10  in FIG. 1 includes a frame  14 , a first coaxial connector  20  and a second coaxial connector  22 . As shown in further detail in FIG. 2, the frame  14  has a plurality of cavities  13  into which a plurality of plug in modules are inserted. Each plug in module is an assembly of a top plate  12 , one or more coaxial connectors  16  and a circuit board  15 . Some types of plug in modules  17  have no coaxial connectors (amplifiers, equalizers and blank module covers), while other types of plug in modules  11  may have one or two coaxial connectors  11 A,  11 B (outputs to external connectors) Each type of plug in module  12 ,  11 ,  17  is inserted into an appropriate modular cavity  13  and secured by fasteners  18 . The frame  14  also houses a multiple cavity circuit board  25  (shown in FIG.  4 ). A housing bottom plate  24  engages frame  14  to enclose the multiple cavity circuit board  25  and form a sealed unit. 
     The relationship of the multiple cavity circuit board  25  to frame  14  is shown in FIG.  4 . At one end of the multiple cavity circuit board  25  is a first coaxial connector  19 A and seizure mechanism  21 A. At the other end of the multiple cavity circuit board  25  is a second coaxial connector  19 B and seizure mechanism  21 B. Either the first coaxial connector  19 A or the second coaxial connector  19 B may be used for RF signal input or output. In addition, both coaxial connectors  19 A,  19 B may be simultaneously used for RF signal input at both ends of frame  14 . 
     The following terms are used herein as follows: 
     A “multiple cavity, multiple port modular CATV housing” means the assembly of modular cavities including a housing frame  14 . 
     A “modular cavity” is an opening for receiving a plug in module. 
     A “plug in module” or a “module” is an assembly that plugs into a modular cavity. A plug in modules may be a subscriber tap, an amplifier, an equalizer, a terminating load, an output module, a shorting blank module or a non-shorting blank module. 
     A “subscriber tap” is a plug in tap module that has multiple subscriber ports. 
     “Subscriber ports” are coaxial connector outputs from a subscriber tap for connection to corresponding subscriber coaxial drop lines. For example, an 8-port subscriber tap has 8 subscriber ports that attach to 8 corresponding subscriber drop lines. 
     A typical subscriber tap module is illustrated in FIG.  3 . The subscriber tap module consists of a tap plate  12 , a plurality of subscriber ports (coaxial connectors  16 ), a circuit board  15 , a pair of signal pins  30 A,  30 B, and a pair of switch pins  32 A,  32 B. The circuit board  15  is held in place with screws to tap plate  12 . The switch pins  32 A,  32 B and signal pins  30 A,  30 B are attached to the circuit board  15 . The coaxial connectors  16  are mounted on the tap plate  12  for connection to the circuit board  15 . 
     A module switch  44  (comprising two flexible arms  44 A,  44 B) is mounted on the multiple cavity circuit board  25 , which is secured within the frame  14 . The module switch consists of the flexible conductive member  44  and two signal pin contacts  41 A,  41 B, which are mounted on the multiple cavity circuit board  25 . To operate the module switch  44 , two holes  38 A,  38 B are provided in the circuit board  25  above the module switch arms  44 A,  44 B. A bottom detail view of the module switch  44  is shown in FIG.  7 . (FIG. 3 shows the side view of the module switch). 
     The module switch is attached to the multiple port circuit board  25  by a fastener  42 . Each arm  44 A,  44 B of the module switch  44  exerts a force so as to press switch contacts  40 A,  40 B at the ends of the module switch arms  44 A,  44 B against the respective signal pin contacts  41 A,  41 B. Thus, when no module is inserted into the modular cavity, module switch  44  provides a short circuit between input and output signal pin contacts  41 A,  41 B via module switch  44 . 
     On the left side of FIG. 3, the subscriber tap module is shown inserted into the modular cavity opening in the frame  14 . In the inserted position, the plug in module signal pins  30 A,  30 B contact the signal pin contacts  41 A,  41 B on the circuit board  25  respectively. At the same time, switch pins  32 A,  32 B, pass through holes  38 A,  38 B respectively deflecting both module switch arms  44 A,  44 B. The deflection of module switch arms  44 A,  44 B moves the switch contacts  40 A,  40 B so as to open the short circuit between signal pins  41 A,  41 B. 
     Circuit board  15  inside the plug in module contains a standard CATV tap circuit. In a tap, a portion of the RF signal at input signal pin  30 A is tapped by a directional coupler and divided in an internal splitter network to feed RF signal to the coaxial connectors  16 . The remaining portion of the input RF signal is coupled to output pin  30 B. Thus, when the plug in tap module is inserted into the modular cavity, circuit board  15  provides signal continuity between input signal pin contact  41 A and output signal pin contact  41 B on circuit board  25 . 
     In the inserted position, the top plate  12  of the module is fastened to the frame  14  by screw fasteners  18 . The bottom of plate  12  has a recessed area  34  that engages protrusion  36  on the frame  14  to align the module with the frame and contains a stainless steel mesh RFI gasket  34 A eliminating RF radiation or ingress. Frame  14  has a recessed area  51  that engages protrusion  52  and contains a rubber environmental sealing gasket  50 . Added structural strength and stability is provided by the signal pins  30 A,  30 B, which contact the multiple cavity circuit board  25  and the switch pins  32 A,  32 B, which are seated in openings  38 A,  38 B in the multiple cavity circuit board  25 . 
     The relative length of the signal pins  30 A,  30 B and the switch pins  32 A,  32 B is selected so that the module switch  44  provides for “make before brake” operation upon module insertion and removal. That is, to avoid service interruption to downstream subscribers upon module insertion, the module signal pins  30 A,  30 B first “make contact” with the circuit board signal pin contacts  41 A,  41 B, before deflecting the module switch arms  44 A,  44 B to open the module switch  44  (“break contact”). Similarly, upon removal of the module, the module switch arm  44 A,  44 B first “make contact” so as to short signal pin contacts  41 A,  41 B, before breaking contact between signal pins  30 A,  30 B and the signal pin contacts  41 A,  41 B. In such manner, the signal to downstream subscribers is not interrupted upon removal or insertion of a plug in module. 
     The circuit diagram of a multiple cavity, multiple port modular CATV housing (with power passing) is shown in FIG.  6 . Each modular cavity  6 A- 6 F includes a normally shorted module switch. For example, modular cavity  6 C includes module switch  44  having bridging signal pin contacts  41 A and  41 B. When a module is inserted into the modular cavity  6 C, switch  44  opens the conductive path between signal pin contacts  41 A and  41 B. 
     To provide power for an active component, such as an amplifier, input 60 volt, 60 cycle AC at coaxial input connector  20  is separated from the RF signal path by capacitor C 1  and inductive choke L 1 . A separate power bus  61  caries power to all modular cavities  6 A- 6 C. By way of example, modular cavity  6 F includes a power pin contact  63  on the circuit board  25  that is similar to the signal pin contact  41 A in FIG.  3 . An amplifier plug in module has a power pin (similar to the signal pin  30 A in FIG. 3) to engage the power pin contact  63  on the circuit board  25 . In FIG. 6 power passing components C 1  and L 1  are illustrated as being internal to the multiple cavity, multiple port modular CATV housing. In the alternative, capacitor C 1  and inductor L 1  may be located external to the multiple cavity, multiple port modular CATV housing, in which case an additional input power terminal would be provided on the housing frame  14 . If no active components are contemplated, then capacitor C 1 , inductive choke L 1 , the power bus  61 , power pin contacts  63  (and any input power terminal) may be omitted. In the latter case the multiple cavity, multiple port modular CATV housing would be non-power passing, and care must be taken to block out 60 volt, 60 cycle power before applying RF signal to the input coaxial connector. 
     A top transparent view of a multiple cavity, multiple port modular CATV housing showing the spatial relationship between the housing frame  14  each modular cavity  5 A- 5 F, multiple cavity circuit board  25 , is shown in FIG.  5 . Module switch  44  in module cavity  5 D is positioned longitudinally along the center axis of the multiple cavity, multiple port modular CATV housing. 
     In FIG. 4, a side cross sectional view of a multiple cavity, multiple port modular CATV housing shows a frame  14  having a plurality of modular cavities  4 A- 4 F to receive a corresponding plurality of plug in modules. In particular, modular cavities  4 B,  4 C,  4 E, and  4 F are illustrated with various types of modules inserted. Modular cavities  4 A and  4 D are empty. Modular cavities  4 C and  4 E contain terminating or non-terminating subscriber tap modules (or signal output modules). Modular cavity  4 F contains a blank module without switch pins or signal pins, which is a shorting type blank module. A shorting type blank module is essentially a cover plate, which serves primarily to seal the interior of the multiple cavity, multiple port modular CATV housing, without interrupting the internal series circuit. 
     Modular cavity  4 B contains a module without coaxial connectors, but with switch pins and signal pins. Thus, the plug in module in modular cavity  4 B could be any one of a number of types of modules. The plug in module in cavity  4 B could be an amplifier, an equalizer or a non-shorting type blank module. The various types of system configurations possible using the multiple cavity, multiple port modular CATV housing are illustrated in FIGS. 8-14. 
     FIG.  8 : 8 Subscriber Ports, Terminating. 
     Modular cavity  8 A contains a 4-port tap, and modular cavity  8 B contains a 4-port terminating splitter. The module switches in modular cavities  8 A and  8 B are open. Thus, the input RF signal on input terminal  810  is divided among 8 subscriber ports. Since cavity  8 B contains a terminating splitter, no output RF signal is provided at output terminal  812 . Removing the terminating tap from cavity  8 B and inserting one or more different plug in modules will allow flexible modification of the distribution arrangement in the field. 
     FIG.  9 : 16 Subscriber Ports, Non-Terminating. 
     In FIG. 9, the arrangement of FIG. 8 is expanded to additional subscribers. As before, modular cavities  9 A and  9 B contain 4-port taps. Modular cavity  9 C contains a non-terminating 8-port tap. The tap values in any modular cavity, e.g.,  9 A, may be the same or different than the tap values in any of the other modular cavity, e.g.,  9 B or  9 C. Due to the presence of the plug in modules, the module switches in modular cavities  9 A,  9 B and  9 C are open. At the same time, the module switches in modular cavities  9 D- 9 F are closed (shorted condition). Thus, the input RF signal on input terminal  910  is divided among  16  subscriber ports, and the remaining RF signal is provided at output terminal  912 . The plug in modules need not be installed in adjacent modular cavities. 
     FIG.  10 : 22 Subscriber Ports, Non-Terminating. 
     In FIG. 10, an 8-port tap is installed in modular cavity  10 A. A 4-port tap is installed in modular cavity  10 E and an additional 2-port tap and 4-port tap is installed in modular cavities  10 C,  10 E and  10 F respectively. A middle modular cavity  10 D is empty and available for future expansion. Thus, the input RF signal on input terminal  1010  is divided among 22 subscriber ports, and the remaining RF signal is provided at output terminal  1012 . 
     FIG.  11 : Dual Input 22 Subscriber Ports. 12 Subscriber Ports Terminating and 10 Subscriber Ports Terminating. 
     The flexibility of the multiple cavity, multiple port modular CATV housing is illustrated in FIG. 11, in which the coaxial connector output  1112  is used as a second input terminal. Modular cavity  11 A contains a 4-port tap and modular cavity  11 B contains an 8-port terminating tap. A terminating tap is similar to a terminating splitter, except that the former has a directional coupler and terminating impedance  1114 , while the latter terminating splitter has neither directional coupler nor terminating impedance. Modular cavity  11 F contains an 8-port tap and modular cavity  11 E contains a 2-port terminating splitter. Thus, the input RF signal on input terminal  1110  is divided among 12 subscriber ports, while the input RF signal on input terminal  1112  is divided among 10 subscriber ports, for a total of 22 subscriber ports 
     FIG.  12 : 40 Subscriber Ports Terminating. 
     Modular cavities  12 A,  12 B and  12 C each contain an 8-port tap. In the event that the RF signal at input terminal  1210  becomes too attenuated after three 8-port taps, an amplifier module may be inserted into modular cavity  12 D to boost the remaining RF signal. The amplifier module is powered from a power pin  1216 , which is coupled to all modular cavities  12 A- 12 F by a separate power buss  61  and receives power via a power form (such as 60 volt, 60 cycle AC) applied to input connector  20 . Power is separated from the RF signal path by capacitor C 1  and inductive choke L 1 . The amplified RF signal thereafter has sufficient level to provide for two 8-port taps in modular cavities  12 E and  12 F. If the RF signal at input terminal  1210  were sufficiently strong, an amplifier would not be needed, and modular cavity  12 D would also contain an 8-port tap instead of an amplifier module. The 8-port tap in modular cavity  12 F is a terminating splitter, which has no remaining RF signal for output terminal  1212 . 
     FIG.  13 : Dual Input 28 Subscriber Ports. 16 Subscriber Ports Non-Terminating and 12 Subscriber Ports Terminating. 
     The further flexibility of the multiple cavity, multiple port modular CATV housing is illustrated in FIG. 13, in which the coaxial connector output  1312  is used as a second RF input terminal and a mid-housing cavity provides an additional RF output terminal. In particular, a signal output module having at least one coaxial output  1314  is installed in modular port  13 D. 
     Modular cavities  13 A,  13 B and  13 C contain a 4-port tap, an 8-port tap and a 4-port tap respectively. The output of the 4-port tap in modular tap  13 C is input to the output module  13 D. Thus, the input RF signal on input terminal  1310  is divided among  16  subscriber ports, and the remaining RF signal is provided at output terminal  1314 . 
     Coaxial connector  1312  is used as an input terminal. Modular cavity  13 F contains a 4-port tap and modular cavity  13 E contains an 8-port terminating tap. Thus, the input RF signal on input terminal  1312  is divided among 12 subscriber ports, which combined with the 16 subscriber ports from modular cavities  13 A,  13 B and  13 C, is a total of 28 subscriber ports. 
     FIG.  14 : 28 Subscriber Taps Terminating 
     Coaxial cable and RF circuits such as directional couplers attenuate the higher RF frequencies more than the lower RF frequencies. In situations where the higher RF frequencies become much more attenuated relative to the lower RF frequencies (a spectral tilt), a passive equalizer having an inverse spectral tilt is used to equalize all signals in the spectrum. In FIG. 14, the multiple cavity, multiple port modular CATV housing accommodates an equalizer module in module cavity  14 C. 
     In FIG. 14, a 4-port tap is installed in modular port  14 A and an 8-port tap is installed in modular cavity  14 B. The RF output signal from the 8-port tap in modular cavity  14 B is connected to the equalizer in modular cavity  14 C which provides a passive (filter)?? inverse frequency tilt response in the RF spectrum. After the equalizer, the multiple cavity, multiple port modular CATV housing contains a 4-port tap, an 8-port tap and a 4-port terminating splitter in modular cavities  14 D,  14 E and  14 F, respectively. Thus, the input RF signal on input terminal  1410  is divided among 28 subscriber ports, with equalization compensation provided for the RF signal supplied to the last 16 subscriber ports out of the 28 total subscriber ports.