Patent Publication Number: US-2012044361-A1

Title: Tap Units Having Reverse Path Burst Mode Detection Circuits and Related Methods of Identifying Reverse Path Noise Sources and Reducing Reverse Path Noise Funneling

Description:
FIELD OF THE INVENTION 
     The present invention is directed to cable television (“CATV”) networks and, more particularly, to tap units that are used in such CATV networks and methods of transmitting reverse path communications through such tap units. 
     BACKGROUND 
     CATV networks refer to communications networks that are used to transmit cable television, Internet telephone and/or broadband Internet signals (and perhaps other information) between one or more service providers and a plurality of subscribers, typically over coaxial and/or fiber optic cables. Most conventional CATV networks comprise hybrid fiber-coaxial networks in which fiber optic cables are primarily used to carry signals from the headend facilities of the service provider to various distribution points, while less expensive coaxial cable may be used, for example, to carry the signals into neighborhoods and from their into individual homes, apartment complexes, hotels, businesses, schools, government facilities and other subscriber premises (i.e., the physical locations of the subscribers). 
     Typically, the service provider is a CATV service provider that may have exclusive rights to offer cable television services in a particular geographic area. The service provider may broadcast a broad variety of CATV channels to the various subscriber premises over the CATV network. Most CATV service providers also offer other services such as, for example, broadband Internet service and digital telephone service. Thus, in many cases, a subscriber may receive CATV service, a broadband Internet connection, and Voice-over-Internet Protocol (“VoIP”) telephone service all through a single RF connection over the CATV network between the service provider and the subscriber premise. 
     To provide these services to individual subscriber premises, radio frequency (“RF”) tap units are typically connected in series along communications lines (e.g., a coaxial cable) of the CATV network. These tap units typically have an input port that connects to a first segment of the communications line, an output port that connects to a second segment of the communications line, and one or more RF tap ports. Each tap unit splits the signal that is received at its input port, allowing some of the received signal energy to pass through the tap unit to the output port (and thus the tap unit thereby provides a communications path between the first and second segments of the communications line), while the remainder of the received signal energy is split further and provided to the RF tap ports of the tap unit. Cables, such as, for example, coaxial cables, may run between each RF tap port of a tap unit and a respective subscriber premise. In this manner, each RF tap port acts as a branch off of the communications line that is used to provide a communications path between the service provider and an individual subscriber premise over the CATV network. RF signals are transmitted through each RF tap port between the CATV network and an individual subscriber premise. Typically, a tap unit will include multiple tap ports (e.g., four or eight RF tap ports). Thus, each tap unit may be used to provide a communications path between a plurality of subscriber premises and the CATV network. 
     Communications between the CATV network and individual subscriber premises may be one-way or two-way communications. The information that is transmitted from the CATV network headend facilities to the individual subscriber premises is typically referred to as the “downstream” and/or as the “forward path” communications. The “downstream” signals may include, for example, broadcast signals with the different tiers of CATV channels that are delivered to all subscriber premises that subscribe to the respective tiers of CATV service, along with point-to-point signals such as movies on demand, digital telephone signals, broadband Internet service and the like. The “upstream” or “reverse path” communications from each subscriber premise to the CATV network headend facilities likewise typically comprises point-to-point communications such as, for example, digital telephone signals, broadband Internet service (the signals transmitted by the subscriber) and ordering commands (i.e., ordering information for movies-on-demand and other services). Both the upstream and downstream communications for each subscriber premise are typically run through a tap unit. 
     SUMMARY 
     Pursuant to embodiments of the present invention, RF tap units are provided that include an RF input port, an RF output port that is coupled to the RF input port, and a plurality of RF tap ports that are coupled to the RF input port. These tap units further include a burst mode detection circuit that is coupled between the RF input port and at least one of the plurality of RF tap ports. 
     In some embodiments, the burst mode detection circuit includes a burst detector circuit and a switching device that is controlled by an output of the burst detector circuit. In such embodiments, the tap unit may further include a first diplexer and a second diplexer, and the burst detector circuit may be coupled between the first and second diplexers. The switching device may have an output that is coupled to a low frequency port of the second diplexer, and may transfer signals present at its input to its output when in a first state, and may isolate the signals present at the input from the second diplexer when in a second state. In some embodiments, the switching device may be configured when it is in its second state to couple the signals present at its input to a first matched termination and/or to couple the low frequency port of the second diplexer to a second matched termination. 
     In some embodiments, the burst detector circuit may be configured to control the switching device to be in the first state when the burst detector circuit detects that a signal is being transmitted from at least one of the plurality of RF tap ports to the RF input port. In certain embodiments, the switching device may include a first switching device having an input port that is coupled to the first diplexer, a first output port and a second output port that is coupled to a first matched termination and a second switching device having a first output port that is coupled to the first output port of the first switching device, a second output port that is coupled to a second matched termination and an input port that is coupled to the second diplexer. Each matched termination may comprise a resistor that is terminated to a ground voltage. 
     In some embodiments, the RF tap unit may further include a first directional coupler having an input that is coupled to a low frequency port of the first diplexer, a first output that is coupled to an input of the burst detector circuit, and a second output that is coupled to an input of the switching device. The RF tap unit may also include a power divider network, and the first and second diplexers may be positioned either between the RF input port and the power divider network or between the power divider network and at least some of the plurality of RF tap ports. Moreover, the RF tap unit may be an addressable tap unit that includes a radio frequency receiver and a switched filter circuit that is controlled in response to data received at the radio frequency receiver. 
     Pursuant to further embodiments of the present invention, methods of reducing reverse path noise funneling in a communications network are provided in which it is determined that a reverse path communication is being transmitted to a headend facility of the communications network through an RF tap unit of the communications network. A reverse path connection is provided through the tap unit in response to determining that this reverse path communication is being transmitted. 
     In some embodiments, the reverse path connection is provided by re-connecting a disconnected reverse path connection through the tap unit in response to determining that the reverse path communication is being transmitted. These methods may further include disconnecting the reverse path connection through the tap unit in response to determining that no reverse path communication is being transmitted. In some embodiments of these methods, a plurality of subscriber premises may be connected to the headend facility through the RF tap unit, any one of which may transmit the reverse path communication. 
     In some embodiments, the RF tap unit may include a burst mode detection circuit that is configured to detect if the reverse path communication is being transmitted to the headend facility through the RF tap unit. This burst mode detection circuit may include a burst detector circuit that is configured to determine if the reverse path communication is being transmitted through the RF tap unit, and a switching device that is controlled by an output of the burst detector circuit to disconnect the reverse path connection through the tap unit in response to determining that no reverse path communication is being transmitted through the RF tap unit. The burst detector circuit may control the switching device to complete the reverse path connection through the RF tap unit in response to determining that the reverse path communication is being transmitted through the RF tap unit, and may further control the switching device to couple the reverse path connection through the RF tap unit to a matched termination in response to determining that no reverse path communication is being transmitted through the RF tap unit. 
     Pursuant to still further embodiments of the present invention, methods of identifying reverse path noise sources in a CATV network are provided in which the signal quality of a signal transmitted from a subscriber premise through the CATV network is measured. A determination is then made as to which ones of a plurality of tap units were configured to provide reverse path connections during a time period when the measured signal quality of the signal transmitted from the subscriber premise through the CATV network exceeded a threshold. 
     In some embodiments, the method may further include repeatedly measuring the signal quality of the signal transmitted from the subscriber premise through the CATV network and then determining which ones of a plurality of tap units were configured to provide reverse path connections during the respective time periods when the measured signal quality of the signal transmitted from the subscriber premise through the CATV network exceeded the threshold. In these methods, the reverse path noise sources may be identified as the ones of the plurality of tap units that were configured to provide reverse path connections during all of the respective time periods when the measured signal quality of the signal transmitted from the subscriber premise through the CATV network exceeded the threshold. If addressable tap units are provided, the method may also include sending a control signal to one of the addressable tap units that includes a command for the addressable tap unit to reduce the upstream bandwidth between the CATV network and a first port on the addressable tap unit and then measuring the signal quality of another signal transmitted from the subscriber premise through the CATV network. 
     Pursuant to yet additional embodiments of the present invention, burst mode detection circuits are provided that include an RF input port, an RF output port, a burst detector circuit that is coupled between the RF input port and the RF tap port, and a switching device that is controlled by an output of the burst detector circuit. These burst mode detection circuits may also include a first diplexer that is coupled between the burst detector circuit and the RF output port and a second diplexer that is coupled between the RF input port and the burst detector circuit. The switching device may transfer signals present at its input to the second diplexer when in a first state and may isolate the signals present at its input from the second diplexer when in a second state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified, schematic block diagram of a CATV network. 
         FIG. 2  is a block diagram of a tap unit according to certain embodiments of the present invention. 
         FIG. 3  is a block diagram of a burst mode detection circuit according to certain embodiments of the present invention that may be used in the tap unit of  FIG. 2 . 
         FIG. 4  is a block diagram of a tap unit according to further embodiments of the present invention. 
         FIG. 5  is a block diagram of an addressable tap unit according to embodiments of the present invention. 
         FIG. 6  is a block diagram of an embodiment of filter circuits that may be used in the addressable tap unit of  FIG. 5 . 
         FIG. 7  is a block diagram of a stand alone burst mode detection circuit according to embodiments of the present invention. 
         FIG. 8  is a flow chart illustrating methods of identifying reverse path noise sources according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., “between” versus “directly between”, etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, operations, elements, components and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this disclosure and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     As discussed above, CATV networks are bi-directional networks that are used to carry downstream (forward path) communications such as broadcast television signals, broadband Internet and digital telephone service to a plurality of subscriber premises, and upstream (reverse path) communications from a subset of those subscriber premises back to the headend facilities of the CATV network. In a typical CATV network in the United States, the downstream communications are transmitted over the 52-1002 MHz frequency band, while the upstream communications are transmitted over the 5-42 MHz frequency band. Other frequency bands are used in other countries, and it will be appreciated that the tap units according to embodiments of the present invention may be configured to operate over any appropriate downstream and upstream frequency bands. 
     Unfortunately, unwanted noise signals are often generated in individual subscriber premises, particularly at the lower end of the upstream frequency band. This noise may be generated, for example, by poor grounding, faulty equipment and/or improper installation of equipment and/or premise cabling. This noise funnels back into the CATV network. In many instances, this noise can render portions of the upstream bandwidth essentially unusable (e.g., the 5-12 MHz frequency range), thereby limiting the bandwidth available for upstream communications. As CATV networks migrate to higher levels of data compression such as 64 or 128 QAM and/or implement DOCSIS 3.0 channel bonding signaling technologies in order to increase throughput, the reverse path communications may become more sensitive to unwanted noise signals that are generated in individual subscriber premises. 
     Pursuant to embodiments of the present invention, systems and methods are provided that may be used to reduce the amount of reverse path noise funneling in a CATV network. In particular, pursuant to embodiments of the present invention, burst mode detection circuits are provided that can be used to detect when signals are being transmitted on the reverse path from a subscriber premise over the CATV network and to selectively connect the reverse path between the subscriber premise and the headend equipment only when such reverse path communications are being transmitted. Since reverse path communications may only be occasionally transmitted from a subscriber premise (e.g., during an Internet session or a VoIP digital telephone conversation), the burst mode detection circuits according to embodiments of the present invention may be used to reduce or eliminate the noise funneling from individual subscriber premises for large blocks of time, thereby reducing the amount of reverse path noise introduced into the network. 
     Herein the term “burst mode detection circuit” refers to a circuit that is configured to (1) detect the presence of one or more reverse path communications from a subscriber premise or from a group of subscriber premises and to (2) provide a reverse path connection between the subscriber premise(s) and headend facilities of the network when such reverse path communication(s) are present. A “reverse path communication” refers to an information signal that is transmitted from a subscriber premise to headend or other facilities of the communications network. The burst mode detection circuits according to embodiments of the present invention may also be further configured to disconnect the reverse path connection between the subscriber premise(s) and the headend facilities of the network when it is determined that no intentional reverse path communications are present. 
     As is known to those of skill in the art, signal amplifiers are often provided in subscriber premises to boost the received signal level in either or both the forward and/or reverse paths. Burst mode detection circuits could be implemented in these signal amplifiers as a mechanism for reducing reverse path noise funneling in CATV networks. However, many subscriber premises may not include a signal amplifier, and hence this approach would only work to reduce reverse path noise funneling at the subset of subscriber premises that include signal amplifiers. Moreover, many CATV service providers are implementing upgrades to their networks that are designed to boost signal levels at the subscriber premises, and these upgrades may further reduce the number of subscriber premises having signal amplifiers. Additionally, providing a burst mode detection circuit at each subscriber premise may not be economically feasible in some CATV networks. Thus, while burst mode detection circuits could be implemented in signal amplifiers to reduce reverse path noise funneling, it may not be a realistic option in all CATV networks. 
     As discussed in detail below, in some embodiments of the present invention, the burst mode detection circuits may be implemented in the tap units that provide taps from a communications line in the network to individual subscriber premises. As essentially all subscriber premises connect to the network through such tap units, this approach allows a network operator to use the burst mode detection circuits to reduce reverse path noise funneling from essentially all of the subscriber premises in the network, if so desired. Moreover, as tap units typically include 2, 4 or 8 tap ports (although other numbers of tap ports are possible), the total number of burst mode detection circuits that are provided may be reduced in some embodiments to decrease the overall cost of this network upgrade. 
       FIG. 1  is a simplified, schematic block diagram of a CATV network. As shown in  FIG. 1 , the CATV network  10  includes headend facilities  20  where signals (e.g., broadcast and other signals) from various sources, such as transmissions from satellites, microwave, fiber optic and other sources, are gathered and processed for transmission over the CATV network  10 . These signals are distributed via a main or “trunk” network  25  to a plurality of remote hubs  30 . The signals may be further distributed from each remote hub  30  to a plurality of optical nodes  40 , where the signals are typically amplified. Each optical node  40  may feed a plurality of feeder sections  50 . Each feeder section  50  may feed a plurality of drop sections  60 . The communications lines  65  running from each drop section  60  are routed through neighborhoods and the like. A plurality of tap units  70  are typically provided on each cable  65 . The tap units  70  divide the communications lines  65  into a plurality of segments  75 , which are typically implemented as hardline cable segments  75 . The hardline cable segments  75  are used to connect adjacent tap units  70  in series. Each tap unit  70  has one or more tap ports. Coaxial cable segments  85  are used to connect each tap port to one of a plurality of individual subscriber premises  80 . Thus, the tap units  70  provide each subscriber premise access to the CATV network  10 . The individual subscriber premises  80  may comprise, for example, single dwelling homes, multiple dwelling units such as apartment buildings, condominiums, hotels and the like, businesses, schools, government facilities etc. Typically, the tap units  70  are located outside, perhaps within an enclosure, near the subscriber premises  80  (i.e., on the outside of a building, in a cable box near the street, etc.). Note that in  FIG. 1  only two remote hubs  30 , optical nodes  40 , feeder sections  50  and drop sections  60  are pictured to simplify the drawing, and downstream components are depicted off only one of these two stations or sections for the same reason. 
     It will be appreciated that the CATV network depicted in  FIG. 1  is greatly simplified. It will likewise be appreciated that the methods and systems according to embodiments of the present invention discussed below may be used with a wide variety of different CATV networks. Thus, it will be appreciated that the cable network depicted in  FIG. 1  and the systems and components depicted in the other figures of the present application are exemplary in nature, and are not intended to be limiting as to the scope of the present invention as defined in the claims appended hereto. 
     According to embodiments of the present invention, tap units are provided that include burst mode detection circuits. These tap units may be used to reduce reverse path noise funneling from individual subscriber premises into a CATV network.  FIG. 2  is a block diagram of a tap unit  100  that includes a burst mode detection circuit according to certain embodiments of the present invention. Each of the tap units  70  in CATV network  10  of  FIG. 1  could be implemented as one of these tap units  100 . 
     As shown in  FIGS. 1 and 2 , the tap unit  100  includes an RF input port  110 , an RF output port  120 , and a plurality of RF tap ports  130 A- 130 D. The RF input port  110  may receive a hardline cable segment that connects the tap unit  100  to a drop section  60  (such as the leftmost hardline cable segment  75  in  FIG. 1 ), or a hardline cable segment that connects the tap unit  100  to another tap unit  100  (such as the rightmost or middle hardline cable segments  75  in  FIG. 1 ). The RF output port  120  typically receives a hardline cable segment  75  that connects the tap unit  100  to another tap unit  100 . The RF input port  110  and RF output port  120  facilitate connecting the tap unit  100  in series along the communications line  65  that extends from the drop section  60  (see  FIG. 1 ) so that a plurality of tap units  100  may be connected to the same drop section  60  along the communications line  65  that comprises a plurality of cable segments  75 . 
     As further shown in  FIG. 2 , the tap unit  100  includes a directional coupler  140  and a burst mode detection circuit  150 . The directional coupler  140  has a first output port  142  and a second output port  144 . The directional coupler  140  splits the RF signal that is received at the RF input port  110 . Typically, the directional coupler  140  will be configured to pass most of the signal energy input at RF input port  110  through the first output port  142  to the RF output port  120 , while the remaining signal energy is passed through the second output port  144  to the burst mode detection circuit  150 . Thus, the directional coupler  140  is used to split off a small portion of the signal energy received at the RF input port  110  that will be fed to the subscriber premises  80  that are connected to the CATV network  10  through the tap unit  100 . The remaining signal energy that passes to the RF output port  120  may be passed along hardline cable segment(s)  75  to one or more additional downstream tap units  100  (see  FIG. 1 ). The directional coupler  140  also acts to combine reverse path communications from the subscriber premises  80  that are connected to the CATV network  10  through the tap unit  100  with other reverse path communications that are carried on communications line  65  for transmission to the headend facilities of the CATV network  10 . Note that herein the term “directional coupler” is used to refer to couplers that split/combine received signal energy either equally or unequally. Directional couplers that equally split/combine received signal energy may also be referred to herein as “splitters.” 
     In some embodiments, the directional coupler  140  may comprise a “plug-in” directional coupler  140 . By “plug-in” it is meant that the directional coupler  140  is configured to be field-installable and/or field-removable by inserting the directional coupler  140  into a mating slot, recess, housing and/or other receptacle. Such “plug-in” directional couplers  140  further include electrical contacts (not shown) that mate with corresponding electrical contacts in the mating slot, recess, housing and/or other receptacle. As such, a technician may readily install and/or replace these plug-in directional couplers  140  in the field simply by pulling out any directional coupler that is to be replaced and plugging a new directional coupler  140  into the mating slot, recess, housing and/or other receptacle. One or more retainment mechanisms such as snap latches, clips, screws or the like may be included that ensure that the directional coupler  140  remains firmly in place after it is plugged in. Such retainment mechanisms may need to be disengaged or removed in order to remove one directional coupler  140  and replace it with another plug-in directional coupler  140 . It will also be appreciated that in some embodiments of the present invention the directional coupler  140  is not a plug-in directional coupler  140 . 
     As known to those of skill in the art, the amount of energy that the directional coupler  140  ideally passes into the tap unit  100  depends upon a variety of factors, such as the distance of the tap unit from the last amplifier in the CATV network  10 , the distance of the tap unit  100  from the subscriber premises  80  that the tap unit  100  serves, the number of tap ports on the tap unit  100 , etc. By configuring the tap unit  100  to have a plug-in directional coupler an installer or operator may choose the appropriate directional coupler (i.e., one that directs an appropriate amount of signal energy into the tap unit  100 ) for the tap unit at the time that the tap unit  100  is installed and plug it into the socket in the tap unit  100 . With this plug-in directional coupler capability, a CATV operator can stockpile the directional couplers having the appropriate values, but may only need to stockpile a small number of different tap units. 
     As further shown in  FIG. 2 , the tap unit  100  may also include a non-interruptible contact  145  for the plug-in directional coupler  140 . This non-interruptible contact  145  maintains a radio frequency path from RF input port  110  to RF output port  120  even if the plug-in directional coupler  140  is not installed or is temporarily removed, for example, during maintenance operations. Thus, the non-interruptible contact  145  allows the tap unit  100  to pass signals between the headend facilities and downstream tap units  100  (and their associated subscriber premises  80 ) even when the plug-in directional coupler  140  is not installed in the tap unit  100 . Insertion of a plug-in directional coupler  140  disables the non-interruptible contact  145 . The contact  145  is referred to as a “non-interruptible” contact because it is configured so that a significant (or, in some cases, even a noticeable) break in service will not occur for downstream tap units  100  when the plug-in directional coupler  140  is plugged into, or removed from, the tap unit  100 . 
     As shown in  FIG. 2 , the non-interruptible contact  145  provides an alternate signal carrying path that bypasses the plug-in directional coupler  140 . In some embodiments of the present invention, the non-interruptible contact  145  may be implemented as a signal carrying path that is mechanically open-circuited when a directional coupler  140  is plugged into the tap unit  100 . For example, in one specific embodiment, the non-interruptible contact  145  may be implemented as a metal contact beam that is shaped to have good contact force and elastic “memory.” When the non-interruptible metal contact beam  145  is “engaged” (which occurs when the plug-in directional coupler  140  is not installed in the tap unit  100 ), the non-interruptible metal contact beam  145  makes mechanical and electrical contact between a radio frequency input point and a radio frequency output point to provide an alternate radio frequency path. In contrast, when plug-in directional coupler  140  is installed in the tap unit  100 , the plug-in directional coupler  140  mechanically moves the non-interruptible metal contact beam  145 , thereby open-circuiting the alternate radio frequency path. The non-interruptible metal contact beam  145  may be designed so that upon removal of the plug-in directional coupler  140  the non-interruptible metal contact beam  145  immediately re-establishes the alternate radio frequency path to ensure that no significant and/or noticeable break occurs in downstream service. 
     As further shown in  FIG. 2 , the tap unit  100  includes a burst mode detection circuit  150 . A first input/output port  152  of the burst mode detection circuit  150  is coupled to the second output port  144  of the directional coupler  140 . As noted above, the burst mode detection circuit  150  may comprise a circuit that is configured to (1) detect the presence of one or more reverse path communications from a subscriber premise or from a group of subscriber premises and to (2) provide a reverse path connection between the subscriber premise(s) and headend facilities of the network when such reverse path communication(s) are present. An exemplary burst mode detection circuit will be discussed in detail below with reference to  FIG. 3 . The burst mode detection circuit  150  may detect the presence of one or more reverse path communications from the subscriber premises by, for example, examining the spectra of the reverse path over time to detect “bursts” of signal energy that are separated by an amount of time that corresponds to a frame structure of a time division multiple access scheme used to transmit the reverse path communications. When such bursts of energy are identified in the reverse path spectra (e.g., within the 5-42 MHz frequency band), the burst mode detection circuit  150  may determine that communications are present on the reverse path. While the above describes one exemplary method by which a burst mode detection circuit  150  can operate to detect the presence of reverse path communications, it will be appreciated that other methods detecting the presence of reverse path communications may also be used. 
     As is further shown in  FIG. 2 , the second input/output port  154  of the burst mode detection circuit  150  is connected to an input of a power divider network  160 . The power divider network  160  may comprise, for example, a layered network of directional couplers that further divide the received RF input signal into a desired number of signals. The power divider network  160  divides the forward path RF signal so that a portion of this forward path signal is received at each of the outputs of the power divider network  160 . Likewise, with respect to reverse path communications, the power divider network  160  combines these RF signals into a composite RF signal. Typically, the directional couplers used in the power divider network  160  comprise splitters. While a 1×4 power divider network  160  is depicted in  FIG. 2 , it will be appreciated that the power divider network  160  may have any number of outputs (e.g., 1×2, 1×4 and 1×8 power divider networks  160  may be used). 
     Each output of the power divider network  160  is connected to one of the plurality of bi-directional RF tap ports  130 A-D. Respective coaxial cables  85  connect each bi-directional RF tap port  130 A-D to a respective subscriber premise  80  (see  FIG. 1 ). The bi-directional RF tap ports  130 A-D are be used to pass RF signals from the tap unit  100  to one or more end devices that are located, for example, in the subscriber premise  80 , and to pass signals from such end devices to the tap unit  100 . Any appropriate end device that may send and/or receive an RF signal may be placed in communication with the bi-directional tap ports  130 A-D. For example, end devices such as Internet telephones, cable television sets, cable modems and/or other data communication devices may be connected to the tap unit  100  via the RF tap ports  130 A-D. In some cases, an RF signal amplifier, power divider network and/or other devices (not shown in  FIG. 2 ) may be placed between the RF tap port  130 A-D and these end devices. 
     The tap unit  100  may further include a VAC power supply  190 . The power supply  190  may receive an alternating current power signal that is transmitted over the CATV network  10  to, for example, power amplifiers and other equipment in network  10 . The power supply  190  may generate and output a direct current voltage VCC (e.g., a 5 volt signal) that is used to power various components in the tap unit  100  such as, for example, various components of the burst mode detection circuit  150 . 
     While  FIG. 2  illustrates one exemplary tap unit  100  that includes a burst mode detection circuit  150 , it will be appreciated that burst mode detection circuits  150  may be included in a wide variety of conventional or non-conventional tap unit designs. 
       FIG. 3  is a block diagram of a burst mode detection circuit  200  according to certain embodiments of the present invention. The burst mode detection circuit  200  may be used, for example, to implement the burst mode detection circuit  150  of the tap unit of  FIG. 2 . 
     As shown in  FIG. 3 , the burst mode detection circuit  200  includes a first high-low diplexer  210 , a directional coupler  220 , an attenuator  230 , a burst detector circuit  240 , first and second switching devices  250 ,  260 , a second high low diplexer  270 , and an amplifier  280 . The first high-low diplexer  210  is used to separate the high frequency forward path signal from any low frequency reverse path signals. The diplexer  210  has a common port  212 , a high frequency port  214  and a low frequency port  216 . In some embodiments, the diplexer  210  can be configured to filter the signals in a manner such that signals with frequencies greater than approximately 45-50 MHz are passed from the high frequency port  214  to the common port  212 , and to pass low frequency signals in the reverse path from the common port  212  to the low frequency port  216 . 
     The low frequency signals that pass in the reverse path to the low frequency port  216  may be passed to the passive directional coupler  220 . The directional coupler  220  splits off a small part of the received low frequency signal energy and passes it through a first output port  222  to an attenuator  230 . The attenuator  230  feeds the signal energy to the burst mode detector  240 , and may be used to reduce the signal level of these signals (if necessary). In some embodiments, the attenuator  230  may be omitted or may be located in a different position (e.g., at the input to the directional coupler  220 ). The remaining signal energy received at the input of the directional coupler  220  passes through the second output port  224  of directional coupler  220  to the first switching device  250 . 
     The burst detector circuit  240  receives the split-off version of the reverse path signal that is passed through the output of the attenuator  230 . As noted above, in most CATV networks, the signals in the reverse path comprise Time Division Multiple Access (“TDMA”) signals in which multiple users share a frequency band by communicating only during a certain time slice of a communications frame. As a result, the reverse path signals have a “bursty” nature in that the signals appear as a spike of signal energy at a certain frequency at spaced-apart time increments that correspond to a users time slot in each of a series of communications frames. In some embodiments of the present invention the burst detector circuit  240  may comprise a circuit that analyzes the spectrum of the signal on the reverse path to identify when “bursts” of signal energy appear in a manner that suggests that reverse path signals are being transmitted by one or more of the subscriber premises  80  that are connected to the CATV network  10  via the tap unit  100 . 
     The output of the burst detector circuit  240  may be a control signal that is output on port  242  of the burst detector circuit  240 . When the burst mode detector  240  detects that one or more signals are being transmitted on the reverse path, the control signal output at port  242  may take on a first value (e.g., logic 1), and will otherwise will have a second value (e.g., logic 0). The control signal output at port  242  is provided to the switching devices  250 ,  260 . It will be appreciated that other control signal schemes may be used without departing from the scope of the present invention. 
     The second output  224  of directional coupler  220  is fed to the switching devices  250 ,  260 . These switching devices  250 ,  260  may be implemented, for example, as two discrete switching devices as shown in  FIG. 3 . In another exemplary embodiment, the switching devices  250 ,  260  may be implemented as a single integrated switching device. Other designs are also possible. In some embodiments, the switching devices may comprise switches/relays (the terms “switch” and “relay” are used interchangeably herein) such as an SPDT non-latching relay. As shown in  FIG. 3 , in the depicted embodiment, the first switching device  250  includes an “input” port  251 , first and second “output” ports  252 ,  253 , and a control port  254 . The switching device  250  is set to connect input port  251  to one of the first and second output ports  252 ,  253 , with the control signal that is input to port  254  controlling which of the output ports  252 ,  253  is connected to the input port  251 . In particular, when the control signal input to port  254  has the first logic value (indicating that reverse path signals are present), the switching device  250  is set in its “ON” position to connect input port  251  to output port  252 , thereby allowing the reverse path communications to flow through the switching device  250 . In contrast, when the control signal input to port  254  has the second logic value (indicating that no reverse path signals are present), the switching device  250  is set in its “OFF” position to connect input port  251  to output port  253  thereby breaking the communications path such that energy on the reverse path does not flow through the switch  250 . This effectively disconnects the subscriber premises  80  that are connected to tap unit  100  from the CATV network  10 . 
     The output port  252  of the first switching device  250  is connected to a first output port  262  of the second switching device  260 . The second switching device  260  further includes a first input port  261 , a second output port  263  and a control port  264 . The switching device  260  is configured so that when the control signal input to port  264  has the first logic value (indicating that reverse path signals are present), the switching device  260  is set in its “ON” position to connect input port  261  to output port  262 , thereby allowing the reverse path communications to flow through the second switching device  260 . In contrast, when the control signal input to port  264  has the second logic value (indicating that no reverse path signals are present), the second switching device  260  is set in its “OFF” position to connect input port  261  to output port  263 . 
     It will be appreciated that, in some embodiments, the control signal output on port  242  of the burst detector circuit  240  may not immediately trigger the switching devices  250 ,  260  to switch from their “ON” positions to their “OFF” positions when an absence of reverse path communications is detected. Instead, the switching devices  250 ,  260  may be controlled, for example, to remain in their “ON” positions for some predetermined period of time (which may be variable) in the anticipation of future reverse path communications, but then switch to their “OFF” positions if no such additional reverse path communications are received within a given time period. 
     As shown in  FIG. 3 , output port  253  of switching device  250  and output port  263  of switching device  260  are each coupled to matched terminations  255 ,  265 , which in this particular embodiment are implemented as 75 ohm resistors  256 ,  266  that are connected in series to a ground voltage  257 . As such, when the switching device  250  is in its “OFF” position, the second output port  224  of directional coupler  220  is connected to matched resistive termination  255 . Reflections and interference from the tap unit  100  into the subscriber premises  80  which may degrade the downstream communications can be reduced by including the matched termination  255  on switching device  250 . Similarly, as the second output port  263  of switching device  260  is connected to matched resistive termination  265  when the switching device  260  is in its “OFF” position, the CATV network likewise terminates through the low frequency input of the high-low diplexer  270  to a matched termination. As such, reflections and interference from the tap unit  100  into CATV network  10  can similarly be reduced by including the matched termination  265  on switching device  260 . 
     Herein, the term “matched termination” is used to refer to a termination that approximately matches the specific transmission path&#39;s impedance (in this case 75 ohms), thus being capable of substantially absorbing the possible propagation modes with relatively minimal reflection. The term “resistive termination” is used to refer to a termination that includes at least one purposefully resistive element such as a resistor. By providing such a matched resistive terminations  255 ,  265 , both the subscriber premises  80  and the CATV network  10  may be properly terminated when the switching devices  250 ,  260  are in their OFF positions so as to disconnect the reverse path from the CATV network  10 , and hence reflections that result in return loss, frequency response and/or other signal degradation can be reduced in these circumstances. Additionally, as the reverse path is disconnected, noise funneling from the subscriber premises  80  into the CATV network  10  may be reduced or eliminated during periods when no reverse path communications are being transmitted, which may improve the overall performance of the CATV network  10 . 
     As is also shown in  FIG. 3 , the input  261  of switching device  260  is connected to diplexer  270 . The diplexer  270  has a common port  272 , a high frequency port  274  and a low frequency port  276 . The input  261  of switching device  260  is connected to the low frequency port  276  of diplexer  270 . The diplexer  270  outputs the reverse path signals received from the switching device  260  to the CATV network, while preventing the low frequency signals from funneling into the forward path from the CATV network  10  to the subscriber premises  80 . 
     The burst mode detection circuit  200  may also, in some embodiments, include an amplifier  280 , which may be located in a variety of different locations along the reverse path. In the particular embodiment of  FIG. 3 , the amplifier  280  is located between the input  261  of the second switching device  260  and the low frequency port  276  to the high-low diplexer  270 . In various embodiments, the power amplifier  280  can optionally be omitted. 
     It will also be understood that various of the components of  FIG. 3  may be omitted or replaced with other components, and that the location of the various components may also be modified. For example, in some embodiments, the attenuator  230  may be located between the diplexer  210  and the directional coupler  220 . In other embodiments, the attenuator  230  may be omitted altogether. Likewise, the power amplifier  280  could be located elsewhere along the reverse path and/or could be omitted. Various other modifications are also possible without departing from the scope of the present invention. 
     In the particular embodiment depicted in  FIGS. 2 and 3 , the switching devices  250 ,  260  are non-latching relays that require a DC power source. The burst detector circuit  240  may also require a DC power source, as does the amplifier  280  (if included in the burst mode detection circuit  200 ). As shown in  FIG. 2 , AC power may be input to the tap unit  100  at the RF input port  110 , and provided to a VAC power supply  190 . This power supply  190  outputs a DC voltage VCC that may be used to power the switching devices  250 ,  260 , the burst detector circuit  240  and the power amplifier  280  of  FIG. 3 . It will be appreciated that in other embodiments, the switching devices may not require a separate power source. 
       FIG. 4  is a block diagram of a tap unit  100 ′ according to further embodiments of the present invention. As shown in  FIG. 4 , the tap unit  100 ′ may include the exact same components as the tap unit  100 . Accordingly, like components have been labeled using the same reference numerals as in  FIG. 2  and operation of these components will not be further described here. The difference between the embodiments of  FIGS. 2 and 4  is that in the embodiment of  FIG. 2 , a single burst mode detection circuit  150  is included between the plug-in directional coupler  140  and the power divider network  160 , while in the embodiment of  FIG. 4 , four such burst mode detection circuits  150  are provided between the power divider network  160  and the respective RF tap ports  130 A-H. Each of these four burst mode detection circuits  150  may have, for example, the design of circuit  200  of  FIG. 3 . By providing four burst mode detection circuits  150 , the reverse path may be disconnected for each subscriber premise  80  during periods of time when no reverse path communications are being transmitted from that particular subscriber premise  80 , and hence the tap unit  100 ′ of  FIG. 4  may further reduce reverse path noise funneling as compared to tap unit  100  (as tap unit  100  only disconnects the reverse paths from the four subscriber premises  80  during time periods when none of the subscriber premises  80  are transmitting reverse path communications). 
       FIG. 5  is a block diagram of an addressable tap unit  300  that includes a burst mode detection circuit according to embodiments of the present invention. Each of the tap units  70  in the CATV network  10  of  FIG. 1  could be implemented as one of these tap units  300 . The tap unit  300  includes each of the components that are included in the tap unit  100  of  FIG. 2 . These like components are labeled with the same reference numerals used in  FIG. 2 , and, for the sake of brevity, the operation of these components will not be discussed further here. In addition, the tap unit  300  includes a number of additional components that allow the tap unit  300  to operate as an “addressable” tap unit. 
     The tap unit  300  comprises an “addressable” tap unit in that each of the RF tap ports  130 A- 130 D of tap unit  300  may be turned on or off or otherwise configured from a remote location. A cable television service provider may use these addressable taps to control, from a remote location, which signals are passed in the downstream and/or the upstream direction between the cable service provider and specific subscriber premises. Consequently, a cable service provider may use the addressable tap units to add, drop and/or change the services provided to a particular subscriber premise without the need to send a service technician to the subscriber site. 
     The tap unit  300  differs from the tap unit  100  in that it includes a second directional coupler  310  that is coupled to the second output  144  of directional coupler  140 . Most of the signal energy received by directional coupler  310  passes to the burst mode detection circuit  150 , but a small amount of the signal energy is split off and passed to a filter  320 . The filter  320  is used to pass a frequency band on which control signals are embedded in the downstream signal transmitted from the CATV network  10 , while filtering out the remainder of the downstream and upstream signals. The output of the filter  320  is coupled to a receiver  330 . In this particular embodiment, the receiver  330  comprises a radio frequency FSK receiver having demodulation capabilities. Command signals received from the cable television network  10  are coupled to the FSK receiver  330  where they are received and demodulated. The demodulated commands are output by the FSK receiver  330  to a controller  340  which may be implemented, for example, as a microprocessor, microcontroller, logic circuit or the like. The controller  340  outputs one or more control signals that are used to control the setting of a plurality of filter circuits  350 . A filter circuit  350  is provided between the outputs of the power divider network  160  and the RF tap ports  130 A-D. The filter circuits  350  may comprise “plug-in” filter circuits, and a non-interruptible contact (not shown) may be provided for each plug-in filter circuit  350  to maintain communications even if the plug-in filter circuit  350  is not installed or is temporarily removed. 
       FIG. 6  is a block diagram of one implementation of a filter circuit  400  that may be used to implement the filter circuits  350  of  FIG. 5 . As shown in  FIG. 6 , the filter circuit  400  may include a high pass filter  410 , a bandpass filter  420 , a filter free signal carrying path  430  and switches  440 - 445 . The high pass filter  410  may comprise, for example, a filter that passes signals having a frequency above, for example, 50 MHz while attenuating lower frequency signals. The bandpass filter  420  may comprise, for example, a filter that passes signals in one or more selected frequency ranges within, for example, the 5-1000 MHz frequency band while attenuating signals in other frequency ranges. By way of example, the bandpass filter  420  may be configured to pass signals in frequency bands that provide a subscriber with 911 digital telephone service and standard cable television service, while attenuating/blocking signals in all other frequency ranges and thus disabling other services such as normal digital telephone service, premium cable television service and pay-per-view and movies-on-demand services. 
     The switches  440 - 445  comprise two-position switches that are configured to open one of two possible signal paths and close the other signal path in response to a control signal that is applied to the switch. The switches  440 - 445  are controlled by control signals C 1 -C 4  which are generated by the controller  340  of  FIG. 5  (hence for a four port tap unit, the controller  340  generates a total of 12 control signals that independently control the three switches on each of the four filter circuits  350 ). As shown in  FIG. 6 , control signal C 1  controls switches  440  and  441 , control signal C 2  controls switch  442 , control signal C 3  controls switch  443 , and control signal C 4  controls switches  444  and  445 . 
     In this particular embodiment, each filter circuit  400  may be set to one of four different modes by appropriate selection of the control signals C 1 -C 4  in order to control the signals that pass through the tap associated with each filter circuit  400 . In an exemplary embodiment, these four different modes may be as follows:
         1. “ON” mode—Passes the full downstream frequency band (e.g., 51-1000 MHz) from the cable service provider to the subscriber premise, and passes the full upstream frequency band (e.g., 5-40 MHz) from the subscriber premise to the cable service provider.   2. “OFF” mode—Does not pass any signals between the cable service provider and the subscriber premise in either the upstream or the downstream frequency bands.   3. “HIGH PASS” mode—Passes the full downstream frequency band from the cable service provider to the subscriber premise, while blocking the full upstream frequency band from the subscriber premise to the cable service provider.   4. “WINDOW” mode—Passes selected portions of the downstream frequency band from the cable service provider to the subscriber, and passes selected portions of the upstream frequency band from the subscriber to the cable service provider. The WINDOW mode may be used to pass frequencies associated with one or more specific tier(s) of services which an individual subscriber has ordered.       

     The filter circuit  400  may be set to the ON mode by setting control signal C 2  so that switch  442  connects to path  451 , setting control signal C 1  so that switches  440  and  441  connect to the filter free signal carrying path  430 , setting control signal C 3  so that switch  443  connects to path  456 , and setting control signal C 4  so that switch  444  connects to switch  442  and switch  445  connects to switch  443 . In this manner, signals incident at the input of either switch  444  or switch  445  flow through the filter free signal carrying path  430 , and hence all signals in the downstream and upstream frequency bands may be passed between the subscriber premise and the cable television service provider. Similarly, to set the filter circuit  400  to the OFF mode, control signal C 4  is set so that switches  444  and  445  are connected to their grounded terminations. In this manner, signals incident at the input of either switch  444  or switch  445  are connected to ground and are not passed. In order to set the filter circuit  400  to the HIGH PASS mode (i.e., the signals are routed through the high pass filter  410 ), control signal C 2  is set so that switch  442  connects to path  450 , control signal C 3  is set so that switch  443  connects to path  454 , and control signal C 4  is set so that switch  444  connects to switch  442  and switch  445  connects to switch  443 . Finally, in order to set the filter circuit  400  to the WINDOW mode (i.e., the signals are routed through the bandpass filter  420 ), control signal C 2  is set so that switch  442  connects to path  451 , control signal C 1  is set so that switch  441  connects to path  453  and switch  440  connects to path  455 , control signal C 3  is set so that switch  443  connects to path  456 , and control signal C 4  I sset so that switch  444  connects to switch  442  and switch  445  connects to switch  443 . Other switch settings may also be used to implement the various modes. 
     It will also be appreciated that the addressable tap unit of  FIG. 5  may be modified to have burst mode detection circuits  150  included on each addressable tap in the same manner that the non-addressable tap unit  100  of  FIG. 2  was modified to provide the addressable tap unit  100 ′ of  FIG. 4 . In such an embodiment, the burst mode detection circuits  150  could be placed between the respective outputs of the power divider network  160  and the filter circuits  350 , or could be placed between the filter circuits  350  and their respective tap ports  130 A-D. 
     According to further embodiments of the present invention, the burst mode detection circuit  150  of tap unit  100  may be implemented as a stand-alone unit. For example, in the embodiment of  FIG. 4 , each of the four burst mode detection circuits  150  could be implemented as a stand-alone burst mode detection circuit that is connected in series on the coaxial cable segments  85  that connect each tap port  130 A-D to a respective subscriber premises  80 .  FIG. 7  is a block diagram illustrating a stand-alone burst mode detection circuit  500  that illustrates how the stand-alone circuit may be placed in series on the cable connection between a tap port of a tap unit and a subscriber premises  80 . 
     As shown in  FIG. 7 , the circuitry included in the burst mode detection circuit  500  may be identical to circuitry included in the burst mode detection circuit  200  of  FIG. 3 . The primary difference between these circuits is that the burst mode detection circuit  500  may include a weatherproof housing (not shown) and may include an RF input port  510  that may receive the coaxial cable segment  85  that is connected to an RF tap port of a conventional tap unit (not shown in  FIG. 7 ) and an RF output port  520  that receives a coaxial cable segment  85 ′ that connects the stand-alone burst mode detection circuit  500  to a subscriber premise  80  (not shown in  FIG. 7 ). Additionally, the burst mode detection circuit  500  further includes a power provision circuit. In the depicted embodiment, the power provision circuit comprises an AC/DC power supply  285  that converts AC power that is provided from the headend facilities over coaxial cable  85  into DC power that is used to power, for example, amplifier  280  and/or burst detector  242 . However, it will also be appreciated that the burst mode detection circuit  500  may be powered in other ways. For example, in other embodiments, a DC/DC power supply (not shown) may be used to power the, amplifier  280  and/or burst detector  242  using power supplied through RF output port  520 . The stand-alone burst mode detection circuit  500  may be used to upgrade an existing conventional tap unit to have the functionality provided by the tap units according to embodiments of the present invention. 
       FIG. 8  is a flow chart illustrating methods of identifying the sources of “upstream” noise that is introduced into the cable television network (e.g., noise that is introduced at subscriber premises  80 ). When noise is detected on conventional CATV networks, a manual effort may be undertaken to determine the node where the noise is entering the network. For example, a service technician may be sent out who physically probes each tap for noise signals. A network management handheld device may be used to track how the noise level in the CATV network varies as each tap is probed in order to identify taps that are introducing significant noise into the network. This process may be expensive and time consuming, and may also degrade or interrupt service to selected customers. 
     The advent of addressable taps allows much of this manual process to be automated. In particular, an operator (or an automated program) may use the addressable tap units, from a remote location, to turn each addressable tap on and off (typically in the upstream direction only) while measuring the noise present on the network both before and after the addressable taps are turned off. In this manner, a cable service provider may more quickly and efficiently track the noise contribution of individual subscribers, isolate the taps which appear to be the major contributors to the noise introduced onto the network, and/or determine the frequency bands that are the primary contributors to noise inserted into the network from a particular subscriber location. Methods of using an addressable tap unit to identify upstream noise sources in this manner are disclosed, for example, in U.S. patent application Ser. No. 11/943,244, filed Nov. 20, 2007, the entire contents of which are incorporated herein by reference. 
     The tap units according to embodiments of the present invention may be used to even further streamline the process for identifying reverse path noise sources. In a typical CATV network, the network already tracks the performance of each cable modem that transmits on the reverse path (and is able to specifically identify each such cable modem, and associate that cable modem with the specific tap unit that provides it access to the network). Since most tap units in the network are not transmitting at any given time, when a noise spike occurs, the network will know that the noise is likely being introduced from one of the subscriber premises that has a reverse path connected to the network at the time the noise spike occurred. Since the addressable tap units according to embodiments of the present invention that have their reverse path connected to the network will change over time (as different subscriber premises send or stop sending reverse path communications), the performance data can be analyzed to quickly identify the tap unit or units that are introducing significant noise into the network. 
     One such method of identifying reverse path noise sources is depicted in the flow chart of  FIG. 8 . As shown in  FIG. 8 , operations may begin by setting a counter n equal to 1 that is used to track each of the reverse path signals that may be received from the cable modems at the N subscriber premises that are connected, for example, to a particular server at the CATV network headend facilities (block  600 ). At the same time, a timer may also be set to zero (block  600 ). Then, the signal-to-noise (“S/N”) ratio (or other performance parameter or parameters) is measured (e.g., at the headend facilities) for the reverse path signal that is being received from the first of the N subscriber premises that are connected to the server (to the extent that such a reverse path signal is presently being transmitted) (block  605 ). If the measured S/N ratio for the reverse path signal from the first subscriber premise is unacceptable, operations proceed to block  625 . If, instead, the measured S/N ratio is acceptable (block  610 ), then the counter n is incremented to n+1 (block  615 ) and a determination is made as to whether the reverse path signals from all N subscriber premises that are connected to the server have been tested (block  620 ). If they have, then operations may end. If not, operations return to block  605  where the S/N ratio is measured for the reverse path signal that is being received from the next (i.e., n+1) of the N subscriber premises that are connected to the server (to the extent that such a reverse path signal is presently being transmitted). 
     At block  625  (which is reached if at block  610  it is determined that the S/N ratio is unacceptable), the headend facilities can use known information such as information regarding which of the N subscriber premises were transmitting reverse path communications during any particular time slot and information regarding which particular tap units feed these subscriber premises to determine the particular tap units that were transmitting reverse path communications during the time slot when the unacceptable S/N ratio was measured at block  610 . A determination is then made as to whether one or more than one tap units were transmitting reverse path communications at this time (block  630 ). If, at block  630 , it is determined that only a single tap unit was transmitting at the relevant time, then that tap unit is identified as the tap unit that is the likely source of the reverse path noise, and operations may proceed to block  660  where additional optional operations may be performed to try to identify the specific subscriber premise(s) that are connected through the identified tap unit that are the source or sources of the reverse path noise. If it is instead determined at block  630  that multiple tap units were transmitting during the time slot when the unacceptable S/N ratio was measured at block  610 , then, after an additional period of time, the S/N ratio is re-measured for the same (n th ) reverse path signal to determine whether or not the S/N ratio is now acceptable (block  635 ). At block  640 , a comparison is made between the tap units that were identified in the determination that was made at block  625  and any determination made at block  635  where the S/N ratio was found to be unacceptable. Any tap unit that was identified in each and every one of these determinations is then identified at block  645  as a tap unit that had its reverse path connected to the headend facilities each and every time that an unacceptable S/N ratio was measured. These tap units represent potential reverse path noise sources. 
     A determination is then made as to whether one or more than one tap units have been identified at block  645  as the potential reverse path noise source(s) (block  650 ). If multiple tap units have been identified, the timer may be checked to see if a predetermined amount of time has passed (block  655 ). This timer may be used because at some point it becomes inefficient to continue to try to reduce the number of tap units that are potential noise sources through the process of the operations of blocks  635  through  650  of  FIG. 8  by seeing how the S/N ratio changes over time as different tap units transmit on the reverse path, and instead the operations set forth starting at block  660  may be used to more specifically locate the reverse path noise source. 
     If at block  650  it is determined that only a single tap unit remains identified as the potential noise source and/or if at block  655  it is determined that the timer has hit a threshold, operations then proceed to block  660  where a counter m is set to 1 that is used to cycle through the M tap ports provided on the identified tap units. Then, operations proceed to block  665  where tap port m on the identified addressable tap unit or units is turned off in the reverse path by, for example, commanding the addressable tap unit to switch the tap port at issue into a high pass mode) and the S/N ratio is re-measured for the same (n th ) reverse path signal to determine whether or not the S/N ratio is now acceptable. If it is determined that the re-measured S/N ratio is acceptable (block  670 ), then operations proceed to block  675  where the m th  tap port on the identified tap unit (or tap units) is identified as the reverse path noise source. If at block  670  it is determined that the S/N ratio is still unacceptable, then a determination is made as to whether all M tap ports on the one or more identified tap units have been tested by turning the tap ports off individually and re-measuring the S/N ratio as described with respect to blocks  665 - 670  (block  680 ). If they have, then operations may end without identifying a specific subscriber premise as the reverse path noise source. If all tap ports have not yet been tested, operations proceed to block  685  where the m th  tap port is turned back on and the counter is incremented to m=m+1. Then operations proceed back to block  665  where the testing can be repeated with the m+1 th  tap port turned off. 
     By the procedure described above, reverse path noise sources may be quickly identified, and this identification may be done from the headend facilities. In many cases, this methodology may be able to identify a specific subscriber premise that is introducing unacceptable amounts of reverse path noise into the network, and may do so without having to turn on and off an excessive number of reverse path addressable tap ports. In some instances such as, for example, when two or more subscriber premises are causing the reverse path noise problem, the exemplary operations set forth in the method of  FIG. 8  may not always specifically identify the subscriber premise(s) that are contributing excessive reverse path noise. However, in these situations, the data that is recorded by the above described method may be further analyzed to identify tap units and/or individual tap ports that are likely sources of the reverse path noise insertion. Once tap ports have been identified as likely sources of reverse path noise insertion, those tap ports may be turned off (if addressable tap units are provided) to see if the noise goes away to thereby confirm the noise source locations. 
     It will further be appreciated that the particular method illustrated in  FIG. 8  is exemplary in nature, and that it could be modified in numerous ways without departing from the scope of the present invention. For example, in some embodiments, various of the operations may be done in a different order than the order depicted. Likewise, in some embodiments, the operations of steps  630  through  655  may be omitted. In still other embodiments such as, for example, networks that do not have addressable tap units, the operations of steps  660  through  680  may be omitted and/or performed manually by an on-site service technician. Numerous other modifications are possible. Thus, it will be appreciated that the present invention encompasses a broad range of methods of identifying reverse path noise sources in a CATV network in which the signal quality of a signal transmitted from a subscriber premise through the CATV network is measured and determined to exceed a threshold to and then a determination is made as to which ones of a plurality of tap units were configured to provide reverse path connections during the time period when the measured signal quality exceeded this threshold. 
     The foregoing disclosure is not intended to limit the present invention to the precise forms or particular fields of use disclosed. It is contemplated that various alternate embodiments and/or modifications to the present invention, whether explicitly described or implied herein, are possible in light of the disclosure. For example, any number of RF output ports may be supported by the various amplifier embodiments discussed herein.