Abstract:
A method and apparatus are disclosed for bypassing a first RF broadband amplifier in a CATV network so as to permit substitution of a second broadband amplifier for the first amplifier to permit repair, replacement and/or analysis of the bypassed first RF amplifier. A switching circuit is employed to rapidly substitute the second amplifier for the first amplifier and to reinsert the repaired of replaced first amplifier in the CATV network following maintenance thereof. Bypassing of the first amplifier and utilization of the second amplifier in its stead allows maintenance to be performed on the first amplifier without disruption of service to the portion of the network downstream of the first amplifier.

Description:
FIELD OF THE INVENTION 
     This invention relates to RF broadband distribution networks, such as CATV networks and more particularly to a method and apparatus for substituting one RF broadband amplifier for another broadband amplifier with minimal disruption to subscribers. 
     CROSS-REFERENCE TO RELATED APPLICATION 
     Not applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     Broadband systems such as CATV systems are employed widely throughout this country and around the world. Such systems typically employ large numbers of RF amplifiers for signal distribution. Typical broadband amplifiers, such as CATV amplifiers, are contained within a housing or chassis which have an input jack, an input test jack for monitoring a replica of the signal presented to the input of the broadband amplifier, an exit jack and an exit test jack for monitoring a replica of the signal appearing at the output of the broadband amplifier. The input jack is typically coupled to the input of the broadband amplifier and the output of the broadband amplifier is typically connected to the exit jack. Where multiple amplifiers are contained within one housing, the above described jacks are replicated. 
     It will be appreciated that decoupling or removal of an amplifier which is disposed in a serial path within a broadband network will prevent the distribution of the signal downstream of the respective amplifier. Accordingly, when maintenance is being performed, and an amplifier is being replaced or repaired in a broadband network, service to all downstream subscribers or users is disadvantageously interrupted. To minimize disruption of service to subscribers or system users, amplifiers are often replaced or repaired in the middle of the night when the fewest subscribers are using the system. The failure of an amplifier necessarily requires immediate attention. A s broadband systems increasingly become used for telephone and other data services, in addition to television service, there will exist an increasing need to be able to maintain the operation of the CATV network during maintenance and to be able to freely service broadband amplifiers disposed throughout the CATV network with minimal disruption to subscribers downstream of the affected amplifier(s). Such is also desirable in a CATV network as the disruption of service poses an annoyance to subscribers. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a method and apparatus are disclosed for substituting in a CATV network one broadband amplifier for another broadband amplifier in a rapid and simple manner so as to avoid disruption of service to subscribers downstream of the respective amplifier. A switching circuit having first and second states is disposed within the housing or chassis of a CATV amplifier. In one switching state, the input and output of an RF amplifier disposed within the housing are coupled to respective input and exit jacks mounted on the housing. Amplitude reduced replicas of the signals appearing at the input and exit jacks are coupled to input and exit test jacks to permit monitoring of the CATV signal presented to the input of the broadband amplifier within the housing and the output of the broadband amplifier within the housing while the amplifier is connected within the network. 
     In the second switching state, the amplifier within the housing is decoupled from both the input and exit jacks and the input and exit jacks are switchably coupled to the respective input and exit test jacks. The input of a substitute RF broadband amplifier may thus be coupled to the input test jack and the output of the substituted amplifier coupled to the exit test jack to effectively interpose the substitute amplifier in the network in place of the amplifier disposed within the housing or chassis. 
     The switching circuit may comprise relays activated by an appropriated relay coil energization voltage or alternatively, may be electronic switches such as bipolar OR field effect transistors suitably actuated. 
    
    
     BRIEF DESCRIPTION OF THE OF THE DRAWING 
     The invention will be more fully understood by reference to the following Detailed Description of the Invention in conjunction with the drawing of which: 
     FIG. 1 is an exemplary block diagram of a portion of a prior art CATV network; 
     FIG. 2. is a diagram of a prior art broadband amplifier; and 
     FIG. 3 is a diagram illustrating the broadband amplifier schematic and assembly in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is illustrative of a prior art Cable Television (CATV) Network 10 which includes a broadband amplifier 12 feeding broadband distribution amplifiers 14, 16, 18, 20 and 22. Broadband distribution amplifier 12, feeds a series of drop amplifiers such as drop amplifiers 24, 26 and 28 which present the cable tv signal to a subscriber. More specifically, amplifier 12 receives a signal over cable 30 and drives the cable 32. Distribution amplifiers 14, 14, 18, 20 and 22 receive signal over cable 30 and drive cables 34, 36, 38, 40 and 42 respectively. Drop amplifiers 24, 26, 28, . . . receive signal over cable 34. For reference purposes herein, cables and amplifiers which drive the input of a given amplifier are deemed to be upstream of the respective amplifier and those cables and amplifiers which receive signal from the output of a given amplifier are considered to be downstream of that amplifier. 
     It will be appreciated that the failure or removal of any amplifier in the network will result in the disruption of service to all subscribers downstream of the respective amplifier. Accordingly it is desirable to be able to minimize the downtime of to network for subscribers downstream of any amplifier which has either failed or must be removed from the network for analysis or service. 
     Referring to FIG. 2, a typical prior art RF broadband amplifier assembly 44 is depicted. An RF broadband amplifier 46, is disposed within a housing or chassis 48. CATV signal is received over a cable 50 at an input jack 52, which is typically a coaxial connector. The RF signal is coupled to the input 54 of the RF amplifier 46 through a coupling capacitor 56. The signal presented to the input 54 of the RF amplifier 46 is also coupled to a voltage divider comprising resistors 58 and 60. An input test jack 62 is coupled to resistors 58 and 60 and is utilized as a test point for analyzing and/or monitoring the input signal to the RF amplifier 54. Alternatively, the input test jack 62 may be coupled to a directional coupler (not shown) as is known in the art. 
     The CATV signal also contains a low frequency AC component in the range of 50 to 60 hz. As illustrated in FIG. 2, the received CATV signal is coupled to an inductor 66 which passes the low frequency AC component of the CATV signal to the input of an AC to DC power supply 67. While the power supply 67 is illustrated as having a unipolar output (Vcc), the power supply 67 may have bipolar outputs (Vcc and Vss--not shown) or any suitable combination of voltages needed to run power the amplifier 46 and any other components disposed within the housing. A decoupling capacitor 64 is provided to filter high frequency RF components from the low frequency AC signal component. The AC voltage is also conveyed downstream to subsequent amplifiers via inductor 75. Decoupling capacitor 77 is provided to filter undesirable high frequency components from the AC signal component. 
     The output 68 of the RF Amplifier 46 is coupled to the exit jack 70 through a coupling capacitor 72. The exit jack, like the input jack, typically comprises a coaxial connector. Additionally, the output 68 of the amplifier 46 provides an output to the exit test jack 74 through a voltage divider formed by resistors 76 and 78 or alternatively, through a directional coupler (not shown) as is known in the art. The signal present at the exit test jack thus may be employed to monitor the output of the RF amplifier 46 and to compare the output 68 to the input 54 for test purposes. While the typical prior art RF amplifier assembly allows monitoring of the inputs and outputs of the operation of a given amplifier, should it be necessary to remove or repair the amplifier, it is necessary to disassemble the amplifier housing, replace or repair the amplifier and reassemble the housing. During at least a portion such period, the subscribers downstream of the respective amplifier typically have their service interrupted. While a single amplifier 46 is illustrated within the housing 46 having a pair of input and exit jacks 52, 70 and a pair of test jacks 62, 74, amplifier assemblies also exist which contain multiple rf broadband amplifiers. In some of those assemblies, the amplifiers have multiple sets of input, exit, input test and exit test jacks, one set for each amplifier. 
     In accordance with the present invention, referring to FIG. 3, an amplifier housing assembly and system are disclosed which permit the primary RF amplifier disposed within a housing to be bypassed, and a temporary amplifier to be rapidly substituted in its stead, so as to avoid significant disruption to the service of the downstream portions of the CATV network. Referring with particularity to FIG. 3, a CATV signal distributed over a coaxial cable 90 or other suitable media is coupled to an input jack 92 mounted on a housing 94 of the RF broadband amplifier assembly 96. The CATV signal at the input jack is coupled to one end of an ac coupling capacitor 98. The other end of the coupling capacitor 98 is coupled to a first switching arm (A) 100 of a DPDT switch which may comprise a mechanical switch such as a DPDT RF relay or alternatively, an electronic switch operative to perform the switching function described herein. Switching arm 100 is normally connected to switch contact B labelled 104 to couple the CATV signal to the input 106 of the RF broadband amplifier 108. As shown in FIG. 3, the input 106 of the broadband amplifier 108 is also coupled to a resistor 110 which in turn is coupled to ground through a resistor 112. Resistors 110 and 112 form a voltage divider. The output of the voltage divider is coupled to switch contact B labelled 114 which is normally connected (when the relay 102 coil 118 is unpowered) to a second switching arm A 116 of the DPDT relay 102. The second switching arm A 116 is coupled to one end of a coupling capacitor 120. The other end of the coupling capacitor 120 is coupled to an input test jack 122 mounted on the housing or chassis 94. Thus, when the relay coil 102 of the DPDT relay 102 is unpowered and switching arms A are making electrical contact with respective contacts B, the CATV input signal is coupled to the input 106 of the CATV amplifier 108 and a reduced replica of the CATV input signal formed by the resistive voltage divider 110, 112, is presented at the input test jack 122. 
     The output 124 of the RF broadband amplifier 108 is coupled to one contact B 126 of a second DPDT relay 128 mounted within the housing or chassis 94. The second DPDT relay, like the first DPDT relay, has switching arms A normally connected to relay contacts B when the respective relay coil 130 in unpowered. Thus, in its normal state, when the relay coil is unpowered, the first switching arm A 132 of the second DPDT relay 128 is coupled to the contact B 126. The first switching arm 132 of the relay 128 is coupled to one end of an ac coupling capacitor 134. The other end of the ac coupling capacitor 134 is coupled to an exit jack 136 mounted on the housing or chassis. The exit jack 136 is connected to a cable 138 to convey the CATV signal to downstream portions of the CATV network. 
     The output 124 of the RF broadband amplifier 108 is also coupled to one end of a resistor 140. The other end of the resistor 140 is connected to one end of a resistor 142, the other end of which is connected to ground. The output of the voltage divider at the connection of resistors 140 and 142 is coupled to contact B 144 of the DPDT relay 128. When the relay coil 130 of the second DPDT relay is unpowered, the second switching arm A 146 is connected to the relay contact B 144. As illustrated in FIG. 3, switching arm A 146 is also coupled to one end of an ac coupling capacitor 148. The other end of the coupling capacitor 148 is coupled to an exit test jack 150 which is mounted on the housing or chassis 94. Thus, when the relay coil 130 of the second DPDT relay is unpowered, a replica of the CATV signal on the output 124 of the RF broadband amplifier 108 may be monitored at the exit test jack 150. The signal presented at the exit test jack 150 is reduced in amplitude in accordance with the voltage divider formed by resistors 140 and 142. 
     When the relay coils 118 and 130 of the respective DPDT relays 102 and 128 are energized, the relays are placed in a second switch state in which respective switching arms A are coupled to respective contacts C of the first and second relays. In this switching state, the RF broadband amplifier 108 is decoupled from the CATV network, the input jack 92 is coupled to the input test jack 122 and the exit test jack 150 is coupled to the exit jack 136. Accordingly, in the state, a bypass RF broadband amplifier may be substituted in the CATV network for the RF broadband amplifier 108 by connecting the input of a substitute RF amplifier 160 to the input test jack 122 and by connecting the output of bypass RF broadband amplifier to the exit test jack 150. 
     More specifically, again referring to FIG. 3, when the relay coil 118 of the first DPDT relay 102 is energized, the switching arms A of the relay 102 are connected to contacts C of the relay. Thus, the received CATV signal is conveyed via the switching arm A to the first contact C 152 of the relay 102. The first contact C 152 is connected to the second contact C 154 of the relay 102. Thus, the input jack 92 is directly AC coupled to the input test jack 122 when the relay coil is energized. 
     Similarly, when the relay coil 130 of the second DPDT relay 128 is energized, the switching arms A of the relay 128 are connected to contacts C of the relay. Thus, when the relay coil 130 is energized, the switching arms A couple an RF signal presented to the exit test jack 150 directly to the exit jack 136 via contacts C labelled 156 and 158 respectively. 
     When it is desired to decouple the internal RF broadband amplifier 108 from the CATV network for analysis, replacement or repair, the input 162 and output 164 of a bypass or substitute RF broadband amplifier 160 may be coupled to respective input and exit test jacks 122 and 150 of the RF amplifier assembly 96 and the relay coils 118 and 130 energized to switch the bypass RF amplifier 160 into the CATV network in place of the existing amplifier 108. It will be appreciated that it will be typically be desirable to substitute for the internal RF amplifier 108, a bypass amplifier 160 having comparable gain, frequency and impedance characteristics. In the foregoing manner, the internal amplifier(s) 108 may be repaired, tested or replaced without disruption of service to the subscribers downstream of the amplifier 108 being decoupled from the network. 
     A battery may be employed to energize the respective relay coils by application of the appropriate DC voltage to the input test jack 122 and the exit test jack 150. More specifically, referring to FIG. 3, a battery provides a DC voltage source. The DC voltage from the battery 170 is coupled through a switch 172, and an inductor 174 to the input test jack 122. An external capacitor 176 provides high frequency decoupling. The DC voltage is further coupled from the input test jack 122 to the relay coil 118 through an inductor 117. An additional decoupling capacitor 119 filters undesirable high frequency components from the DC voltage. Additionally, the DC voltage from the battery 170 is coupled through the switch 172, and an inductor 178 to the exit test jack 150. The DC voltage is further coupled from the exit test jack 150 to the relay coil 130 through an inductor 117. A decoupling capacitor 151 filters undesirable high frequency components from the DC voltage powering the relay coil 130. Capacitors 180 and 182 permit the high frequency CATV signal to be coupled the input and from the output of the amplifier 160 respectively while isolating the input and output of the amplifier from the DC voltage introduced via the battery 170. 
     It should be understood that power for the relays may alternatively be obtained from the low frequency AC component of the CATV signal or the output of the power supply 97. In the event that the relays are powered by an AC power source AC relays are employed. When the relays are powered by a DC power source, such as Vcc or the battery 170, DC relays are employed. 
     The foregoing modification to conventional RF broadband amplifier assemblies will greatly facilitate the service of CATV networks, by minimizing the need to perform elective service on an off hour basis and by minimizing extended and disfavored disruption of CATV service which poses a substantial annoyance to subscribers. In particular, it is noted that the presently disclosed switching circuit may be incorporated within CATV amplifier housings which typically already have input and exit jacks and associated input and exit test jacks and permit the utilization of such test jacks for the dual functions described above. 
     While the invention has been described with respect to a RF amplifier assembly having a single amplifier contained within the housing 94, a plurality of amplifiers may be contained within such a housing or chassis with one switching circuit provided for each input/exit jack and input test/exit test jack pair. 
     It will further be appreciated by those of ordinary skill in the art that other modifications of and departures from the subject matter disclosed herein will be readily apparent without departing from the presently disclosed inventive concepts. Accordingly, the invention disclosed herein is not to be viewed as limited except as by the scope and spirit of the appended claims.