Abstract:
A chassis and associated telecommunication circuit card are disclosed. The chassis has heat dissipation structures and may accommodate a high density of the circuitry cards. Embodiments may include one surface with one or more ridges for rigidity and ventilation and fin slots for receiving circuit card guide fins. Embodiments may include a surface with knockouts for receiving circuit card guides. Embodiments may also include multiple bracket hole patterns for mounting brackets for different racks or for a single multi-rack bracket having more than one mounting hole pattern. The circuit card includes conductor structures such as multiple board layers with paired and segregated conductors. The circuit card also includes some components positioned to cooperate with the ventilation structures of the chassis and includes some components chosen for low-power consumption or reduced flammability.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to chassis for holding telecommunications cards such as repeater circuits. More specifically, the present invention relates to chassis and cards with structures for high card density and structures for mounting with multiple rack styles. 
       BACKGROUND 
       [0002]    It is desirable for a chassis for holding telecommunication circuit cards to support a high density of cards, yet the chassis must effectively dissipate heat developed during operation. The cards installed in the chassis perform electrical operations, such as signal transception and amplification that generate a significant amount of heat. Typically, a chassis is installed in a particular rack that contains several other chassis stacked above and below. The heat that may develop within a chassis in the rack has the potential to harm circuit cards housed in the chassis above and below the chassis where the heat emanates from. Additionally, the rack housing the chassis may be one of several different rack types, such as an EIA rack style, a WECO rack style, or an ETSI rack style, and a different chassis may be required for each to ensure proper mounting. 
         [0003]    The chassis must also provide external protection for the circuit cards it houses. Thus, the chassis cannot freely expose the circuit cards to areas outside the chassis when attempting to dissipate heat. Additionally, the chassis must provide a structural interconnection that maintains electrical continuity between the circuit cards and external transmission mediums such as copper wires or fiber optic cables while facilitating insertion and removal of the cards. A sufficient structure must be used to facilitate this circuit card modularity, which further limits the chassis&#39; ability to provide outlets for heat. 
         [0004]    Additionally, to reduce the chassis size for a given number of circuits, the circuit card density must be increased. Increasing circuit card density is difficult not only due to heat dissipation, but also because of electromagnetic noise that must be contained. Generally, increasing circuit card density involves employing smaller cards, and smaller cards require higher component density within the cards. 
         [0005]    Achieving effective heat dissipation with adequate electromagnetic noise containment may even be more difficult for smaller card designs with higher component densities. 
         [0006]    Thus several factors must be accounted for in the chassis and card design. Chassis designs with large interior spaces for directing heat away from circuit cards may be undesirable because the chassis may become too large when accommodating a high density of circuits. Chassis designs with open exteriors for directing heat away from the circuit cards may be undesirable because the circuit cards may not be sufficiently protected from externalities such as falling objects or heat spreading from a chassis positioned above or below in the rack. Card designs that are relatively large require a larger chassis to house the same quantity of cards. Additionally, a different chassis must be provided for each rack style for proper mounting. 
         [0007]    Thus, there is a need for a chassis and card design whereby the chassis may contain a high density of readily removable circuit cards while providing effective heat dissipation and electromagnetic noise containment and/or be mountable in multiple rack styles. 
       SUMMARY 
       [0008]    The present invention provides a chassis and card design that may accommodate a high density of readily removable circuits while providing heat dissipation and electromagnetic noise containment features. Ventilation structures are employed to direct heat away from internal circuitry. Additionally, chassis designs of the present invention may provide exterior features that establish protection from externalities and prevent the harmful spread of heat to chassis or other equipment stacked above or below. Card designs of the present invention may provide conductor structures for containing electromagnetic noise and/or individual components placed in locations for coordination with the ventilation structures of the chassis. Additionally, the chassis may provide configurable mounting structures to enable a single chassis to be mounted in racks of different styles. 
         [0009]    The present invention may be viewed as a chassis for housing telecommunications cards. The chassis includes a housing having a first and second horizontal surface and vertical sidewalls between the first and second horizontal surfaces. The first and second horizontal surfaces have a plurality of openings, and the first horizontal surface has a first ridge substantially perpendicular to a longitudinal axis of the vertical sidewalls. The chassis also includes a first horizontal cover overlaying the first horizontal surface, and the first horizontal cover has a first ridge that is aligned with the first ridge of the first horizontal surface. 
         [0010]    The present invention may also be viewed as another chassis for holding telecommunications cards. The chassis includes a housing having a first and second horizontal surface and vertical sidewalls between the first and second horizontal surfaces. The first and second horizontal surfaces have a plurality of openings, wherein the second horizontal surface has a first ridge substantially perpendicular to a longitudinal axis of the vertical sidewalls, and the first ridge has a plurality of knockouts. Each knockout is for receiving a guide of a telecommunications card. 
         [0011]    The present invention may also be viewed as a chassis for housing repeater cards. The chassis includes a housing with vertical sidewalls, a first horizontal surface, and a second horizontal surface, wherein the first horizontal surface has a first ridge extending substantially perpendicular to a longitudinal axis of the vertical sidewalls and a second ridge substantially parallel to the first ridge. The first ridge and the second ridge each have an elongated opening. The chassis also includes one or more repeater cards positioned between the first horizontal surface and the second horizontal surface, and the one or more repeater cards have a DC-DC converter and a transceiver. The DC-DC converter is positioned at least partially between the elongated opening of the first ridge and the second surface. The transceiver is positioned at least partially between the elongated opening of the second ridge and the second surface. 
         [0012]    The present invention may be viewed as another chassis for holding telecommunications cards. The chassis includes a housing having first and second horizontal surfaces and first and second vertical sidewalls, and the first vertical sidewall having a plurality of holes. The chassis also includes a first bracket mounted to the housing, with the first bracket having a first side and a second side perpendicular to the first side. The first side of the first bracket has a first horizontal dimension and a first and second set of holes, and the second side of the first bracket has a second horizontal dimension different than the first horizontal dimension and has a first and second set of holes. When the first set of holes of the first side of the first bracket align with at least a portion of the plurality of holes of the first sidewall, the second set of holes of the first side of the first bracket are blocked by the first vertical sidewall. When the first set of holes of the second side of the first bracket align with at least a portion of the plurality of holes of the first vertical sidewall, the second set of holes of the second side of the first bracket are blocked by the first vertical sidewall. 
         [0013]    The present invention may be viewed as another chassis for holding telecommunications cards. The chassis includes first and second horizontal surfaces and first and second vertical sidewalls separating the first and second horizontal surfaces, wherein the first vertical sidewall has a plurality of at least three holes. The chassis also includes a first bracket having a first side and having a second side substantially perpendicular to the first side, the first side having a set of at least two holes and the second side having a set of at least two holes. The set of at least two holes of the first side align with a first set of at least two but fewer than all of the plurality of holes of the first vertical sidewall when the first side abuts the first vertical sidewall. The set of at least two holes of the second side align with a second set of at least two but fewer than all of the plurality of holes of the first vertical sidewall when the second side abuts the first vertical sidewall. The first set includes at least one hole not included in the second set. 
         [0014]    The present invention may be viewed as a method of installing brackets on a chassis. The method involves providing a housing having first and second horizontal surfaces and first and second vertical sidewalls, with the first vertical sidewall having a plurality of holes. The method also involves providing a first bracket having a first side and a second side perpendicular to the first side, wherein the first side of the first bracket has a first horizontal dimension and a first and second set of holes and wherein the second side of the first bracket has a second horizontal dimension different than the first horizontal dimension and has a first and second set of holes. When installing the first bracket such that the first side abuts the first vertical sidewall, the method involves aligning the first set of holes of the first side of the first bracket with at least a portion of the plurality of holes of the first sidewall and blocking the second set of holes of the first side of the first bracket by the first vertical sidewall. When installing the first bracket such that the second side abuts the first vertical sidewall, the method involves aligning the first set of holes of the second side of the first bracket with at least a portion of the plurality of holes of the first vertical sidewall and blocking the second set of holes of the second side of the first bracket by the first vertical sidewall. 
         [0015]    The present invention may be viewed as another method of installing brackets on a chassis. The method involves providing a housing having first and second horizontal surfaces and first and second vertical sidewalls separating the first and second horizontal surfaces, wherein the first vertical sidewall has a plurality of at least three holes. The method further involves providing a first bracket having a first side and having a second side substantially perpendicular to the first side, with the first side having a set of at least two holes and the second side having a set of at least two holes. When installing the bracket such that the first side abuts the first vertical sidewall, the method involves aligning the set of at least two holes of the first side with a first set of at least two but fewer than all of the plurality of holes of the first vertical sidewall. When installing the bracket such that the second side abuts the first vertical sidewall, the method involves aligning the set of at least two holes of the second side with a second set of at least two but fewer than all of the plurality of holes of the first vertical sidewall, wherein the first set comprises at least one hole not included in the second set. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a top front perspective view of an empty chassis in accordance with one embodiment of the present invention. 
           [0017]      FIG. 2  is a top rear perspective view of the empty chassis. 
           [0018]      FIG. 3  is a bottom front perspective view of the empty chassis. 
           [0019]      FIG. 4  is a bottom rear perspective view of the empty chassis. 
           [0020]      FIG. 5  is a top view of the empty chassis. 
           [0021]      FIG. 6  is a front view of the empty chassis. 
           [0022]      FIG. 7  is a right side view of the empty chassis. 
           [0023]      FIG. 8  is a bottom view of a loaded chassis. 
           [0024]      FIG. 9  is a rear view of the loaded chassis. 
           [0025]      FIG. 10  is a left side view of the loaded chassis. 
           [0026]      FIG. 11  is a partially exploded top rear perspective view of the empty chassis. 
           [0027]      FIG. 12  is a partially exploded top rear perspective view of the empty chassis with a top and a bottom mesh cover removed. 
           [0028]      FIG. 13  is a top view of the loaded chassis with the top mesh cover removed. 
           [0029]      FIG. 14  is a front view of the loaded chassis. 
           [0030]      FIG. 15  is a right side view of the loaded chassis. 
           [0031]      FIG. 16  is a top front exploded perspective view of the empty chassis. 
           [0032]      FIG. 17  is a top rear exploded perspective view of the empty chassis. 
           [0033]      FIG. 18  is a right side view of the empty chassis with the right side panel removed. 
           [0034]      FIG. 19  is a bottom view of the empty chassis with the bottom mesh cover removed. 
           [0035]      FIG. 20  is a top view of the empty chassis with the top mesh cover removed. 
           [0036]      FIG. 21  is a top front perspective view of the chassis with cards being inserted. 
           [0037]      FIG. 22  is a top front perspective view of the chassis with three spaced cards being inserted in knock-outs and fin slots within horizontal surfaces of the chassis. 
           [0038]      FIG. 23  is an exploded perspective view of the backplane. 
           [0039]      FIG. 24  is a top view of the backplane. 
           [0040]      FIG. 25  is a rear view of the backplane. 
           [0041]      FIG. 26  is a left side view of the backplane. 
           [0042]      FIG. 27  is a top view of the circuit card. 
           [0043]      FIG. 28  is a right side view of the circuit card. 
           [0044]      FIG. 29  is a bottom view of the circuit card. 
           [0045]      FIG. 30  is a front view of the circuit card. 
           [0046]      FIG. 31  is a rear view of the circuit card. 
           [0047]      FIG. 32  is an exploded top rear perspective view of the circuit card. 
           [0048]      FIG. 33  is an exploded top front perspective view of the circuit card. 
           [0049]      FIG. 34  is a perspective view of the card mounted in relation to a top surface of the chassis. 
           [0050]      FIG. 35  is a perspective view of the card mounted in relation to a bottom surface of the chassis. 
           [0051]      FIGS. 36A and 36B  are a right side view of components mounted in relation to a circuit board of the circuit card. 
           [0052]      FIGS. 37A-37E  are a schematic of alarm circuitry of the circuit board. 
           [0053]      FIGS. 38A-38G  are a schematic of transceiver configuration circuitry of the circuit board. 
           [0054]      FIGS. 39A and 39B  are a schematic of power supply circuitry of the circuit board. 
           [0055]      FIG. 40  is a view of a ground layer of the circuit board. 
           [0056]      FIG. 41  is a view of a power layer of the circuit board. 
           [0057]      FIGS. 42A and 42B  are a view of a component layer of the circuit board. 
           [0058]      FIG. 43  is a perspective view of the empty chassis mounted in an EIA rack using a first mounting method. 
           [0059]      FIG. 44  is a front view of the empty chassis mounted in the EIA rack using the first mounting method. 
           [0060]      FIG. 45  is a perspective view of the empty chassis mounted in the EIA rack using a second mounting method. 
           [0061]      FIG. 46  is a front view of the empty chassis mounted in the EIA rack using the second mounting method. 
           [0062]      FIG. 47  is a perspective view of the empty chassis mounted in a WECO rack. 
           [0063]      FIG. 48  is a front view of the empty chassis mounted in the WECO rack. 
           [0064]      FIG. 49  is a perspective view of the empty chassis mounted in an ETSI rack. 
           [0065]      FIG. 50  is a front view of the empty chassis mounted in the ETSI rack. 
           [0066]      FIGS. 51A and 51B  are a side view of an alternative circuit board of the circuit card having input amplification and additional surge protection components. 
           [0067]      FIGS. 52A and 52B  are a schematic of transceiver configuration circuitry of the repeater circuit employing additional surge protection components. 
           [0068]      FIGS. 53A and 53B  are a schematic of power supply circuitry of the repeater circuit employing additional surge protection components. 
           [0069]      FIG. 54  is a view of an alternative ground conductor layer of the printed circuit board that employs the additional surge protection components. 
           [0070]      FIG. 55  is a view of an alternative power conductor layer of the printed circuit board that employs the additional surge protection components. 
       
    
    
     DETAILED DESCRIPTION 
       [0071]    Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies through the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. 
         [0072]      FIGS. 1-7  show an embodiment of the chassis  100  for holding telecommunications cards. The empty chassis  100  of  FIGS. 1-7  has a horizontal surface  102  mounted to vertical sidewalls  120 ,  122 . In this embodiment, each vertical sidewall  120 ,  122  has a 90 degree bend at the front and rear ends allowing the sidewalls  120 ,  122  to form partial front and rear panels of the chassis  100 . The vertical sidewalls  120 ,  122  have a longitudinal axis that extends from the front to the back of the chassis  100 , which is from the front bend to the rear bend in the embodiment shown. The chassis  100  also has a horizontal surface  142  mounted to the vertical sidewalls  120 ,  122 . Both horizontal surfaces  102 ,  142  and both sidewalls  120 ,  122  of this embodiment are made of a material such as cold-rolled steel. The cold-rolled steel may have a chromate plating to reduce electromagnetic interference. 
         [0073]    Covers are provided over the first horizontal surface  102  and the second horizontal surface  142 . The first horizontal cover  104  overlays the first horizontal surface  102  and mounts directly to it. The second horizontal cover  154  underlays the second horizontal surface  142  and mounts directly to it. The covers  104  and  154  of this embodiment are made of a mesh surface such as aluminum having 63% of its area formed by densely populated openings. Other materials and air passage percentages are also applicable. The mesh material allows rising air to pass through while preventing objects from falling into or out of the chassis  100  that would otherwise enter the chassis  100  through large openings provided in the first and second horizontal surfaces  102 ,  142  that are discussed below. 
         [0074]    The first horizontal surface  102  is contoured to provide two ridges  300 ,  304  dividing three recessed areas  103 ,  302 , and  306 , as is best seen in  FIG. 12 . The two parallel ridges  300 ,  304  extend across the width of the chassis  100  perpendicularly to the longitudinal axis of the vertical sidewalls  120 ,  122 . The first area  103  of the first horizontal surface extends beyond the coverage area of the first horizontal cover  104 . The first horizontal cover  104  of this embodiment is also contoured to provide two ridges  105 ,  108  and two recessed areas  106  and  110 . The ridge  105  of the first horizontal cover  104  is aligned with and overlaps ridge  300  of the first horizontal surface  102 . The ridge  108  of the first horizontal cover  104  is aligned with and overlaps ridge  304  of the first horizontal surface  102 . The recessed area  106  of the first horizontal cover  104  overlaps with recessed area  302  of the first horizontal surface  102 , and the recessed area  110  of the first horizontal cover  104  overlaps with recessed area  306  of the first horizontal surface  102 . 
         [0075]    The first horizontal surface  102  includes a first row of fin slots  118  in area  103  that are for receiving a fin of a circuit card, discussed below. The first row of fin slots  118  extends into the ridge  300  and the fin slots are perpendicular to the longitudinal direction of the ridge  300 . The first horizontal surface  102  also includes a second row of fin slots  196  that extend across the area  302  from the ridge  300  to the ridge  304 . The first horizontal surface  102  also includes a third row of fin slots  202  in area  306  that extends into the ridge  304 . The fin slots of each row align with fin slots in the other rows and guide each circuit card as it is inserted into the chassis  100 . The ridges  300 ,  304  add rigidity to the first horizontal surface by allowing the fin slots to be broken into sets of rows while allowing the fin of the card to pass by as it is being inserted. The rigidity of the first horizontal surface  102  would be reduced if the ridges  300 ,  304  were not present because each fin slot would need to be continuous to facilitate circuit card entry rather than being broken into three sections as shown. 
         [0076]    The first horizontal cover  104  has a row of fin slots  116  in the area  106  that align with the row of fin slots  196  in the area  302  of the first horizontal surface  102 . The first horizontal cover  104  also has a row of fin slots  114  in the area  110  that align with the row of fin slots  202  in the area  306  of the first horizontal surface  102 . The rows of fin slots in the first horizontal cover  104  also allow the fin of the circuit card to be guided as it is inserted into the chassis  100 . Similar to the first horizontal surface  102 , the rigidity of the first horizontal cover  142  would be reduced if the ridges  105 ,  108  were not present because each fin slot would need to be continuous to facilitate circuit card entry rather than being broken into two sections as shown. 
         [0077]    In the embodiment shown, the chassis  100  has open interior regions on each side defined by the wrap-around vertical sidewalls  120 ,  122 . The first horizontal surface  102  has ventilation holes  112  over the left region in the area  103  and ventilation holes  150  over the right region in the area  103 . Also in the area  103 , the first horizontal surface has ventilation holes  152  placed between each fin slot of the first row  118 . The second horizontal surface has ventilation holes  148  under the left region and ventilation holes  146  under the right region. 
         [0078]    Because the chassis is empty in  FIGS. 1-7 , card slot covers  132  are mounted to the chassis  100  to avoid exposing the interior of the chassis  100 . The rear of the chassis  100  is enclosed by a backplane  128  that is attached to each wrap-around vertical sidewall  120 ,  122 . The backplane  128  provides connections between cables and the circuit cards housed by the chassis  100 . The backplane  128  includes external connectors  130  that connect to cables routed to the rear of the chassis rack (not shown) where the chassis  100  is installed. 
         [0079]    The rear of the chassis  100  includes a cover  134  made from a material such as lexan that may be placed over a portion of the backplane  128  where circuit leads and pins from card connectors, discussed below, are present. A cable bar  136  may also be installed to hold the cables connected to the external connectors  130 . A chassis ground connector  138  may also be included for grounding the chassis  100 . 
         [0080]    The second horizontal surface  142  may include a first ridge  183  spanning the width of the chassis  100  and being parallel to the ridge  300  of the first horizontal surface  102 . The first ridge  183  may include a row of knockouts  144  for receiving a guide of a circuit card. The knockout  144  is a portion of the ridge  183  that has been removed to create a passage for the guide. As shown, the card slot covers  132  have a guide  131  that fits into the knockout  144  to stabilize the bottom of the card slot cover  132 . As shown in  FIG. 12 , the second horizontal surface  142  may also include a second ridge  185  positioned near the backplane  128  and extending substantially parallel to the ridge  183  across the width of the chassis  100 . An area  182  is provided between the second ridge  185  and the backplane  128 . The second ridge  185  also includes knockouts  147  for receiving the guide of the circuit cards. 
         [0081]    The chassis  100  of this embodiment also includes mounting brackets  124 ,  126 . These brackets  124 ,  126  mount to the vertical sidewalls  120 , 122  and also to the vertical rails of a chassis rack (not shown). The brackets  124 ,  126  of this embodiment facilitate mounting the chassis  100  in different racks. The bracket  124 ,  126  has a first side  123 ,  129  that abuts the vertical sidewall  120 ,  122 , such as in  FIGS. 1 and 2 , and another side  125 ,  127  that is perpendicular to the first side  123 ,  129  and that abuts the rack rail when mounting the chassis  100 . 
         [0082]    The first side  123 ,  129  has a first horizontal dimension and the second side  125 ,  127  has a second horizontal dimension different than the first horizontal dimension. The differing horizontal dimensions of the sides of the bracket  124 ,  126  allow the bracket  124 ,  126  and chassis  100  to be used for racks with different mounting widths. For one rack mounting width, the first side  123 ,  129  abuts the chassis  100  and the other side  125 ,  127  abuts the rail of the rack. For another rack mounting width that is less wide, the second side  125 ,  127  abuts the chassis  100  and the first side  123 ,  129  abuts the rack rail. 
         [0083]    As best seen in  FIG. 11 , the side  129  of the bracket  126  has a bracket hole pattern established by bracket holes  164 ,  166 , and  168 . Side  123  of bracket  124  has the same bracket hole pattern. The sidewalls  120 ,  122  of the chassis  100  have a bracket hole pattern that matches the bracket hole pattern of the sides  123  and  129 . As seen in  FIG. 12 , this bracket hole pattern of the chassis  100  includes bracket holes  165 ,  167 , and  169 . The bracket holes of the chassis  100  align with the bracket holes of the bracket  124 ,  126  when mounting the brackets  124 ,  126 . 
         [0084]    When using the side  125 ,  127  to mount to the rack rail, a rack hole configuration on the side  125 ,  127  is available. This rack hole configuration includes the rack holes  176 ,  178 , and  180 . This setup is applicable for racks such as an ETSI rack where the distance between adjacent rack holes  176 ,  178 , and  180  is 25 millimeters. The ETSI rack and mounted chassis can be seen in  FIGS. 49 and 50 . 
         [0085]    The ETSI rack of  FIGS. 49 and 50  includes rails  342  and  344 . The rails  342 ,  344  have mounting holes with consistent spacing. The rails  342  and  344  and associated mounting holes of the ETSI rack are spaced further apart horizontally than those of the EIA or WECO racks. Therefore, the chassis  100  includes brackets  124  and  126  mounted such that the wide sides  125  and  127  extend from the chassis  100  while the narrow sides  123  and  129  abut the vertical sidewalls  120 ,  122  of the chassis  100 . 
         [0086]    The rack holes  176 ,  178 , and  180  of the brackets  124 ,  126  align with three contiguous mounting holes  346 ,  348 , and  350  of the rails  342 ,  344 . The chassis  100  is fastened to the rails  342 ,  344  through screws that engage the rack holes  176 ,  178 , and  180  and the mounting holes  346 ,  348 , and  350 . Multiple chassis  100  may be stacked one directly atop the next within the ETSI rack. 
         [0087]    With reference to  FIG. 11 , the side  125  of the bracket  124  has a bracket hole pattern established by bracket holes  158 ,  160 , and  162 . Side  127  has the same bracket hole pattern. The sidewalls  120 ,  122  of the chassis  100  have a bracket hole pattern that matches the bracket hole pattern of sides  125  and  127 . As seen in  FIGS. 11 and 12 , this bracket hole pattern of the chassis  100  includes brackets holes  159 ,  161 , and  163 . 
         [0088]    When using the side  123 ,  129  to mount to the rack rail, a rack hole configuration on the side  123 ,  129  is available. This rack hole configuration includes the rack holes  170 ,  171 ,  172 , and  174 . This setup is applicable for racks such as an EIA or WECO rack where the distance between adjacent rack holes  170 ,  171 , and  172  is 0.5 inches and the distance between the adjacent rack holes  172  and  174  is 1.25 inches. The EIA rack and mounted chassis can be seen in  FIGS. 43 and 44  for a first mounting method and  FIGS. 45 and 46  for a second mounting method. The WECO rack and mounted chassis can be seen in  FIGS. 47 and 48 . 
         [0089]    The EIA rack of  FIGS. 43 ,  44 ,  45 , and  46  includes rails  322  and  324 . The rails  322 ,  324  have paired mounting holes with one spacing distance between each hole of the pair and a greater second distance between adjacent holes of different pairs. Because the rails  322  and  324  and associated mounting holes of the EIA rack are spaced more closely horizontally than those of the ETSI rack, the chassis  100  includes brackets  124  and  126  mounted such that the narrow sides  123  and  129  extend from the chassis  100  while the narrow sides  125  and  127  abut the vertical sidewalls  120 ,  122  of the chassis  100 . 
         [0090]    For the first method of mounting shown in  FIGS. 43 and 44 , the rack holes  171 ,  172 , and  174  of the brackets  124 ,  126  align with three contiguous mounting holes  326 ,  328 , and  330  of the rails  322 ,  324 . The mounting holes  326  and  328  are of one pair, and mounting hole  330  is paired with mounting hole  332 . Both the mounting hole  332  of the rails  322 ,  324  and the rack hole  170  of the brackets  124 ,  126  are unused in this method. The chassis  100  is fastened to the rails  322 ,  324  through screws that engage the rack holes  171 ,  172 , and  174  and the mounting holes  326 ,  328 , and  330 . Multiple chassis  100  may be stacked one atop the next in the EIA rack using this first mounting method and a small gap will be provided between each chassis  100 . 
         [0091]    For the second method of mounting shown in  FIGS. 45 and 46 , the rack holes  171 ,  172 , and  174  of the brackets  124 ,  126  align with three mounting holes  326 ,  328 , and  332  of the rails  322 ,  324 . Mounting hole  330  of the rails  322 ,  324  and rack hole  172  of brackets  124 ,  126  are unused in this method. The chassis  100  is fastened to the rails  322 ,  324  through screws that engage the rack holes  171 ,  172 , and  174  and the mounting holes  326 ,  328 , and  332 . Multiple chassis  100  may be stacked one atop the next in the EIA rack using the second mounting method as well and a small gap will be provided between each chassis  100 . 
         [0092]    The WECO rack of  FIGS. 47 and 48  includes rails  334  and  336 . The rails  334 ,  336  have mounting holes with consistent spacing distance between each adjacent mounting hole. Because the rails  334  and  336  and associated mounting holes of the WECO rack are spaced horizontally the same distance as those of the EIA rack and are more closely spaced horizontally than those of the ETSI rack, the chassis  100  includes brackets  124  and  126  mounted such that the narrow sides  123  and  129  extend from the chassis  100  while the narrow sides  125  and  127  abut the vertical sidewalls  120 ,  122  of the chassis  100 . 
         [0093]    The rack holes  170  and  172  of the brackets  124 ,  126  align with two contiguous mounting holes  338  and  340  of the rails  334 ,  336 . The rack holes  171  and  174  of the brackets  124 ,  126  are unused with the WECO rack. The chassis  100  is fastened to the rails  334 ,  336  through screws that engage the rack holes  17  and  172  and the mounting holes  338  and  340 . Multiple chassis  100  may be stacked one directly atop the next in the WECO rack. 
         [0094]      FIGS. 8-10  and  13 - 15  show the chassis  100  loaded with circuit cards  208 . Each circuit card  208  has a handle  156  that extends from a faceplate  210  of the circuit card  208  that the user may grip to insert or remove a circuit card  208  from the chassis  100 . The faceplate  210  of each of the cards fills the card slot openings that are otherwise occupied by card slot covers  132 . 
         [0095]    In  FIG. 13 , the first horizontal cover  104  is removed to show the first horizontal surface  102  as is also shown in  FIG. 12 . The first horizontal surface  102  includes the recessed area  103  adjacent to the first ridge  300 . The first ridge  300  includes a row of elongated openings  194 . The first ridge  300  is also adjacent to the recessed area  302 . The recessed area  302  includes the second row of fin slots  196 . Between each adjacent pair of fin slots  196  lies openings from a first row  192 , a second row  190 , and a third row  186 . Over the left and right empty regions lie additional large ventilation holes  198  and  188 , respectively. 
         [0096]    Adjacent to the recessed area  302  is the second ridge  304  of the first horizontal surface  102 . The second ridge  304  includes a row of elongated openings  195 . Adjacent to the second ridge  304  is the recessed area  306  that includes a row of fin slots  202 . Between each adjacent pair of fin slots  202  lie openings from a row of openings  200 . Over the left and right empty regions lie additional ventilation holes  204  and  206 , respectively. 
         [0097]      FIGS. 16 and 17  shows exploded views of the chassis  100  without the first horizontal cover  104  and the second horizontal cover  154 . From these exploded views, the wrap-around structure of the vertical sidewalls  120  and  122  can be seen. Additionally, the placement of the ridges  300 ,  304  in the first horizontal surface  102  in relation to the placement of the ridges  183 ,  185  in the second horizontal surface  142  is visible as is the pattern of openings in both surfaces. 
         [0098]      FIG. 18  shows a right side view of the empty chassis  100  with the right vertical sidewall  122  removed. The left vertical sidewall  120  can be seen as no cards are positioned in the chassis  100  to obstruct the view of the sidewall  120 . This side view illustrates the mounted relationship of the card connector  224  and the external connector  130  of the backplane  128 . Also illustrated by  FIG. 18  is the alignment and overlapping position of the ridges  105  and  108  of the first horizontal cover  104  in relation to the ridges  300  and  304 , respectively, of the first horizontal surface  102 . The ridges  183  and  185  of the second horizontal surface  142  can be seen as can the second horizontal cover  154  which does not include a ridge aligned with the ridge  185  in this embodiment. 
         [0099]      FIG. 19  shows an exterior view onto the second horizontal surface  142  of the chassis  100  with the mesh cover  154  removed. The second horizontal surface  142  includes the first row of knockouts  144  at the front of the chassis  100 . On each side of the knockouts  144  are ventilation holes  308  and  310  over the empty side areas of the chassis. As shown, the bracket  124  is mounted with its narrow side extending outwardly from the chassis  100  while the bracket  126  is mounted with its wide side extending outwardly. 
         [0100]    The second horizontal surface  142  includes the second row of knockouts  147  positioned near the rear of the chassis  100 . Four rows of openings are positioned between the first row of knockouts  144  and the second row of knockouts  147  including a first row  312 , a second row  314 , a third row  316 , and a fourth row  320 . In the embodiment shown, the holes of a row alternate between long and short from one column to the next adjacent column. Between the rear of the chassis  100  and the second row of knockouts  147  are several smaller openings  318  that provide additional ventilation. 
         [0101]    Because  FIG. 19  shows an empty chassis  100 , the positioning of the ventilation structures of the first horizontal surface  102  relative to ventilation structures of the second horizontal surface  142  can be seen. The elongated opening  194  of the ridge  300  of the first horizontal surface  102  can be seen through the first row  312  and second row  314  of openings in the second horizontal surface  142 . Likewise, the elongated opening  195  of the ridge  304  can be seen through the second row of knockouts  147 . The first row  186 , second row  190 , and third row  192  of openings of the first horizontal surface that lie between ridges  300  and  304  can be seen through the openings  316  and  320  indicating a partial vertical alignment of openings between the first horizontal surface  102  and the second horizontal surface  142 . The third row of fin slots  202  of the first horizontal surface  102  and the rear row of openings  200  can be also been seen through the second row of knockouts  147 . 
         [0102]    To further illustrate the relation of the ventilation structures of the second horizontal surface  142  in relation to those of the first horizontal surface  102 ,  FIG. 20  shows an empty chassis  100  viewed onto the first horizontal surface  102  with the first horizontal cover  104  removed. The second row of knockouts  147  can be seen through the rear row of openings  200 . The knockouts  147  can also be seen through the elongated opening  195  of the ridge  304 . The third row  316  and fourth row  320  of openings of the second horizontal surface  142  can be seen through the first row  186 , second row  190 , and third row  192  of openings of the first horizontal surface  102 . The first row  312  and second row  314  of openings of the second horizontal surface  142  can be seen through the elongated opening  194  of the ridge  300 . The first row of knockouts  144  can be seen through the first row of fin slots  118 . 
         [0103]    Air rises through the bottom of the chassis  100  and passes by the circuit cards  208  installed between the first horizontal surface  102  and the second horizontal surface  142  as the components of the circuit cards  208  warm the air. In the embodiment shown, because the openings of each horizontal surface are not directly aligned, the warmed air is not able to rise directly from bottom to top within the chassis  100  but may be channeled forward, backward, and/or side-to-side before passing through the nearest hole in the first horizontal surface  102 . 
         [0104]      FIG. 21  shows the chassis  100  filled with circuit cards  208  and having three cards partially inserted. The circuit cards include a fin  212  on one edge that is received by the fin slots of the first horizontal surface  102  and the first horizontal cover  104 . The circuit card  208  also has a guide  214  on an opposite edge that fits within the knockout  144  of the ridge  183  of the second horizontal surface  142 . 
         [0105]      FIG. 22  more clearly shows the cooperation between the fin slots  118  of the first horizontal surface  102  and the fin  212  of the circuit card  208 . The cooperation between the guide  214  and the knockout  144  of the first ridge  183  of the second horizontal surface  142  is also shown. The card  208  is positioned with the fin  212  in the slot  118  and the guide  214  in the knockout, and the card  208  is inserted until the faceplate  210  abuts the front edge  216  of the first horizontal surface  102 . At that point, a connector  225  of the card  208  engages a card connector  224  of the backplane  128  discussed below. Also, in this embodiment holes  218 ,  220 , and  222  of the guide  214  have at least partially aligned with holes  312 ,  314 , and  316  in the second horizontal surface  142  once the card  208  is fully inserted. This alignment is more clearly shown in  FIG. 35 . 
         [0106]      FIGS. 23-26  are several views of the backplane  128 . The backplane  128  is a printed circuit board and it has external connectors  130  mounted to one side and card connectors  224  mounted to the other side. A power supply connector  226  is also mounted to the side with the external connectors  130 . The connector  225  of the circuit card  208  mates to the card connector  224  once the card  208  is fully inserted in the chassis  100 , and the card connector  224  establishes electrical communication between the card  208  and the external connector  130 . As shown in  FIG. 2 , the backplane  128  of the chassis  100  is vertical relative to the horizontal surfaces  102 ,  142 , and the vertical backplane  128  is positioned between and perpendicular to the two vertical sidewalls  120 ,  122 . 
         [0107]      FIGS. 27-33  are several views of the circuit card  208 . The circuit card  208  includes the fin  212 , guide  214 , faceplate  210 , finger  156 , and connector  225  previously discussed. The circuit card  208  also includes a printed circuit board  234  that has circuitry  236  mounted to it. The circuitry  236  may be repeater circuitry as discussed below. Light emitting diodes (LEDs), such as power LED  228 , channel A LED  230 , and channel B LED  232 , may protruded from the faceplate  210 . The LEDs  228 ,  230 , and  232  may illuminate as one or more colors as controlled by circuitry  236  to indicate the state of operation of the circuitry  236 . 
         [0108]      FIG. 34  shows the card  208  mounted in the chassis  100  in relation to the first horizontal surface  102  and its ventilation structures. The fin  212  of the card  208  is positioned within the first row  118 , second row  196 , and third row  202  of fin slots. The card  208  is fully inserted once the faceplate  210  has contacted the front edge  216 . The card  208  includes several components such as a capacitor  236 , a DC-DC converter  238 , a transceiver  248 , relay  244 , and programmable logic device  246  that are positioned, in this embodiment, relative to the structures of the first horizontal surface  102 . These components are discussed in more detail below. 
         [0109]    The capacitor  236  lies beneath the area  103  that restricts upward ventilation and causes air to be channel toward rearward areas of the chassis  100 . The DC-DC converter  238  lies partially beneath the elongated opening  194  of ridge  300 . The elongated opening  194  increases the ventilation over the DC-DC converter  238  which generates a significant amount of heat. The DC-DC converter  238  also partially lies beneath the row of openings  192 . The relay  244  and programmable logic device  246  lie beneath the row  190  and row  186  of openings. The transceiver  248  lies partially beneath the elongated opening  195  of the second ridge  304  which increases the ventilation over the transceiver  248  that also generates a significant amount of heat. 
         [0110]      FIG. 35  shows the card  208  mounted in the chassis  100  in relation to the second horizontal surface  142  and its ventilation structures. The guide  214  of the card  208  is positioned within a knockout of the first row  144  of the first ridge  183  as the card  208  is being inserted. In this embodiment, once the card  208  is fully inserted, the guide  214  rests partially within a knockout of the second row  147  of the second ridge  185 . The first hole  218  of the guide  214  comes to rest over the second row of openings  314  of the second horizontal surface  142 . The second hole  220  of the guide  220  comes to rest over the third row  316  and fourth rows  320  of openings. The third hole  222  comes to rest over the second row of knockouts  147  in the second ridge  187 . Thus, air is able to pass through the openings and knockouts of the second horizontal surface and pass through the guide  214  to absorb heat from the components of the card  208 . 
         [0111]    In the embodiment shown, the capacitor  236  lies over the first row of openings  312 . The DC-DC converter  238  lies over the first row  312  and second row  314  of openings and over the first guide opening  218 . The relay  244  and programmable logic device  246  lie over the third row  316  and fourth row  320  of openings and over the second guide opening  220 . Amplifiers  252 ,  254  and  256 ,  258  included in this embodiment on the card  208  lie over the knockouts  147  and the third guide opening  222 . 
         [0112]      FIGS. 36A and 36B  show a side view of an embodiment of the repeater circuit board  234  of a card  208  suitable for installation in the chassis  100 . As discussed with reference to  FIGS. 34 and 35 , the repeater circuit board  234  has several components positioned on the board  234  in relation to the horizontal surface area  103 , the ridges  300 ,  304  and the rows of openings  186 ,  190 ,  192 ,  312 ,  314 ,  316 , and  320  of the horizontal surfaces  102 ,  142  of the chassis  100 . The repeater circuit board  234  includes a power supply capacitor  236 , a DC-DC converter  238 , and a transceiver  248  previously discussed. The board  234  has the LEDs  228 ,  230 , and  232  that provide the external visual indications of the repeater circuit&#39;s operation. Other components of the board  234  include but are not limited to relays  240 ,  242 , and  244 , a programmable logic device (PLD)  246 , an oscillator  250 , isolation transformers  260 ,  262 , and  264 ,  266 , and first channel and second channel amplifiers  252 ,  254  and  256 ,  258 . 
         [0113]    The embodiment shown in  FIGS. 36A and 36B  may be employed as a bridging repeater circuit that receives a low-level monitor signal through connector  225  and recreates the signal in a higher level suitable for network transmission and sends it out through connector  225 . The bridging repeater circuit board  234  of  FIGS. 36A and 36B  may be used where a digital signal cross-connect (DSX) of the network becomes faulty and must be replaced without interrupting signal transfer. The bridging repeater circuit bypasses the faulty DSX without interrupting signal transfer by receiving monitor signals from healthy DSXs and providing high-level signals to the healthy DSXs until the healthy DSXs are permanently connected together to bypass the faulty DSX. 
         [0114]    The capacitor  236  of the embodiment shown is positioned such that the uncovered horizontal surface area  103  of the first horizontal surface  102  is directly above it because the capacitor  236  does not need the extra ventilation provided by the larger openings  186 ,  190 ,  192  located between the ridges  300 ,  304  that are covered by the mesh cover  104 . The DC-DC converter  238  of this embodiment may be a model that is highly flame resistant to enhance the flame containment of the chassis  100 . An epoxy encased DC-DC converter  238  such as the Ericsson PFK 4611SI is suitable in this embodiment. A monitor jack, which might ordinarily be placed between the LEDs  230  and  232 , is also absent in this embodiment to reduce the material on the board  234  that is susceptible to burning. 
         [0115]      FIGS. 37A-E  shows the alarm circuitry  272  of the repeater circuit board  234 . The alarm circuitry  272  controls the LEDs  228 ,  230 , and  232 . During normal operation, the LEDs  228 ,  230 , and  232  are one color, such as green, to indicate normal operation. The power LED  228  turns red if the logic power plane  270  loses voltage from the output of the DC-DC converter  238 . This occurs due to relay  242  changing state in response to the loss of logic power thereby causing voltage received directly from the backplane connector  225  to activate the red diode of LED  228  instead of the green diode. 
         [0116]    The channel A LED  230  and channel B LED  232  are electrically connected to the PLD  246  and to a logic ground plane  268 . The PLD  246  receives power from the logic power plane  270  and receives control signals from the transceiver  248 . When a channel is operating normally, the PLD  246  causes the green diode of the LED to illuminate. 
         [0117]    If the transceiver  248  detects that channel A has no signal, then LOS 0  line passing from the transceiver  248  to the PLD  246  is triggered causing the PLD  246  to light the red diode along with the green diode of LED  230  to create a yellow illumination. If the transceiver  248  detects that channel B has no signal, then LOS 1  line passing from the transceiver  248  to the PLD  246  is triggered causing the PLD  246  to light the red diode along with the green diode of LED  232  to create a yellow illumination. If either channel has a loss of signal, then a minor alarm signal is generated and provided through the backplane connector  225  by relay  244  changing state due to a control signal from the PLD  246 . The minor alarm line is electrically linked to a chassis ground plane  280 . 
         [0118]    If the transceiver  248  detects that it has failed, then the DFM line passing from the transceiver  248  to the PLD  246  is triggered causing the PLD  246  to light the red diode and turn off the green diode of LEDs  230  and  232  to create a red illumination. A major alarm signal is also generated and provided through the backplane connector  225  by relay  240  changing state due to a control signal from the PLD  246 . The major alarm line is electrically linked to the chassis ground plane  280  as well with coupling capacitors. 
         [0119]    The PLD  246  and relays  240 ,  242 , and  244  may be selected so as to minimize power consumption and reduce the amount of heat being generated by each circuit board  234  in the chassis  100 . The Atmel model ATF16V8BQL PLD draws only 100 milliwatts when active and is a suitable PLD for controlling the relays  240  and  244  and LEDs  230  and  232 . The NAIS TX-S relay draws only 50 milliwatts when active and is a suitable relay for controlling the LED  228  and the major and minor alarm signals. 
         [0120]      FIGS. 38A-G  show an embodiment of the transceiver circuitry located on the board  234 . The transceiver  248 , such as the Level One model LXT332, is electrically connected to the logic power plane  270  and the logic ground plane  268 . The transceiver  248  is also electrically linked to a channel A power plane  274 , a channel A ground plane  278 , a channel B power plane  276 , and a channel B ground plane  282 . Each channel of this embodiment has its own power and ground plane to avoid cross-talk and to avoid electrical noise from the power supply circuit of  FIGS. 39A-G  and chassis  100 . The transceiver  248  is electrically linked to the oscillator  250  that is electrically connected to the logic power plane  270  and logic ground plane  268 . The oscillator  250  provides a reference frequency signal to the transceiver  248 . 
         [0121]    The transceiver  248  receives its input signals for each channel from the input amplifiers  252 ,  254  and  256 ,  258 . The input amplifiers  252 ,  254  and  256 ,  258  receive input signals from the backplane connector  225  through the isolation transformers. Channel A input signal passes through isolation transformer  264  to the input amplifiers  256 ,  258 , and channel A output signal passes through isolation transformer  266 . Channel B input signal passes through isolation transformer  260  to the input amplifiers  252 ,  254 , and channel B output signal passes through isolation transformer  262 . As shown in  FIGS. 36A and 36B , the input isolation transformer  264  and output isolation transformer  266  of channel A are contained in one unit. Similarly, the input isolation transformer  260  and output isolation transformer  262  of channel B are contained in another unit. Likewise, input amplifiers  252  and  254  of channel B are housed in one integrated circuit chip, and input amplifiers  256  and  258  of channel A are housed in another integrated circuit chip. 
         [0122]    The input amplifiers  252 ,  254  for the tip and ring connections, respectively, of channel B are electrically connected to the channel B power plane  276  and also to the channel B ground plane  282  Likewise, the input amplifiers  256 ,  258  for the tip and ring connections, respectively, of channel A are electrically connected to the channel A power plane  274  and also to the channel A ground plane  278 . Providing power to the amplifiers of differing channels from different power and ground planes reduces cross-talk and other electromagnetic interference. The input amplifiers  252 ,  254  and  256 ,  258  increase the amplitude of the monitor signal received by the bridging repeater circuit board  234  of  FIGS. 36A and 36B  to a level within the sensitivity range of the transceiver  248 . The transceiver  248  is then able to recreate the signal having the higher level suitable for network transmission. 
         [0123]    In the bridging repeater circuit embodiment of  FIGS. 38A-G , the line build-out function of the transceiver  248  is fixed at a specific signal level and shape because a consistent cable length is generally used when connecting the bridging repeater circuit between the healthy DSXs. Thus, line build-out variability is not needed. Resistors  284  are arranged to provide a fixed connection between certain line build-out pins of the transceiver  248  to the logic power plane  270  while providing a fixed connection between other line-build out pins of the transceiver  248  to the logic ground plane  268 . 
         [0124]      FIGS. 39A and 39B  show the power supply circuitry. The backplane connector  225  receives −48V DC power and provides it through the board  234  to the DC-DC converter  238 . The −48V line and the −48 V return line are linked by the capacitor  236  to eliminate ripple. These lines are also coupled to the chassis ground plane  280 . The DC-DC converter  238  outputs a voltage that is electrically connected to the logic power plane  270 , the channel A power plane  274 , and the channel B power plane  276 . The DC-DC converter  238  has a return that is electrically connected to the logic ground plane  268 , the channel A ground plane  278 , and the channel B ground plane  282 . Ferrite beads are used to isolate each power plane connected to the DC-DC converter  238  and each power plane is AC coupled to each ground plane. 
         [0125]      FIG. 40  shows a ground layer of the circuit board  234 . The ground layer includes the chassis ground plane  280  that extends around the periphery  286  of the circuit board  234  and is electrically connected to the chassis ground provided through the chassis ground connector  138  of the chassis  100 . The chassis ground plane  280  surrounds the logic ground plane  268 , the channel A ground plane  278 , and the channel B ground plane  282 . The chassis ground plane  280 , logic ground plane  268 , channel A ground plane  278 , and channel B ground plane  282  are copper sheets that are isolated from each other within the single ground layer of the printed circuit board  234 . 
         [0126]      FIG. 41  shows a power layer of the circuit board  234  that is adjacent to the ground layer and separated from it by a dielectric layer. The power layer includes the logic power plane  270 , the channel A power plane  274 , and the channel B power plane  276 . The logic power plane  270  substantially overlaps with the logic ground plane  268  of the ground layer. The channel A power plane  274  substantially overlaps with the channel A ground plane  278 . Likewise, the channel B power plane  276  substantially overlaps with the channel B ground plane  282 . This arrangement minimizes electrical noise and cross-talk. 
         [0127]      FIGS. 42A and 42B  show a component layer of the circuit board  234 . The electrical components previously discussed are typically mounted to the component layer. The transceiver  248  is mounted in transceiver area  294 . The isolation transformers  260 ,  262 , and  264 ,  266  are mounted in transformer areas  296  and  298 . It is generally desirable to minimize the distance between the isolation transformer areas  296 ,  298  and the transceiver area  294 . A distance of one and one-third inches or less is suitable. 
         [0128]    Also located on the component layer are chassis ground pads  290  and  292 . These chassis ground pads  290  and  292  are electrically connected to the chassis ground plane  280 . The metal faceplate  210  of the circuit card  208  mounts to holes within the chassis ground pads  290  and  292  and metal-to-metal contact is established between the chassis ground pads  290 ,  292  and the faceplate  210 . This metal-to-metal contact maintains the faceplate  210  at chassis ground. 
         [0129]      FIGS. 51A and 51B  show an alternative circuit board layout whereby additional surge protection is provided. The embodiment shown in  FIGS. 51A and 51B  contains input amplifiers  252 ,  254  and  256 ,  258  but lacks line build-out switches. This embodiment has Schottky diode banks  360  and  362  positioned between the isolation transformers  260 ,  262  and  264 ,  266  and the transceiver  248 . Each diode bank of this embodiment includes four Schottky diodes. Additionally, this embodiment has a transient voltage suppressor  364  positioned between the DC-DC converter  238  and the bottom of the circuit board  234  which is close to the surface  142  when installed in the chassis  100 . 
         [0130]      FIGS. 52A and 52B  show the transceiver and the configuration of the Schottky diodes from each bank  360  and  362 . This configuration of Schottky diodes can be used with the transceiver configuration shown in  FIGS. 38A-G . One Schottky diode of the bank  360  is tied between the channel A power plane  274 ′ and the channel A tip output. Another Schottky diode of the bank  360  is tied between the channel A power plane  274 ′ and the channel A ring output. Another Schottky diode of the bank  360  is tied between the channel A tip output and the channel A ground plane  278 ′. The last Schottky diode of the bank  360  is tied between the channel A ring output and the channel A ground plane  278 ′. 
         [0131]    Channel B output is configured the same way with one Schottky diode of the bank  362  being tied between the channel B power plane  276 ′ and the channel B tip output. Another Schottky diode of the bank  362  is tied between the channel B power plane  276 ′ and the channel B ring output. Another Schottky diode of the bank  362  is tied between the channel B tip output and the channel B ground plane  282 ′. The last Schottky diode of the bank  362  is tied between the channel B ring output and the channel B ground plane  282 ′. 
         [0132]      FIGS. 53A and 53B  illustrate the power supply circuit that includes additional surge protection. The DC-DC converter  238  of the circuit has an output line and a return line that ultimately provide the channel A power and ground, channel B power and ground, and the logic power and ground. A transient suppressor  364  is tied between the output line and the return line of the DC-DC converter  238 . 
         [0133]      FIG. 54  shows the ground layer of the circuit board  234  utilizing the additional surge protection. In this embodiment, the chassis ground plane  280 ′ surrounds the periphery  286  of the ground layer and is electrically connected to the chassis ground provided through the chassis ground connector  138  of the chassis  100 . The chassis ground plane  280 ′ surrounds the channel A ground plane  278 ′, logic ground plane  268 ′, and the channel B ground plane  282 ′. As with the previous embodiment, chassis ground plane  280 ′, logic ground plane  268 ′, channel A ground plane  278 ′, and channel B ground plane  282 ′ are copper sheets that are isolated from each other within the single ground layer of the printed circuit board  234 . 
         [0134]    In this embodiment, the logic ground plane  268 ′ is positioned such that it is partially between the channel A ground plane  278 ′ and the channel B ground plane  282 ′. The diode bank  360  is located on the component layer and in the area  368  positioned over the channel A ground plane  278 ′. Similarly, the diode bank  362  is located in the area  366  positioned over the channel B ground plane  282 ′. 
         [0135]      FIG. 55  shows a power layer of the circuit board  234  that is adjacent to the ground layer shown in  FIG. 54  and separated from it by a dielectric layer. The power layer includes the logic power plane  270 ′, the channel A power plane  274 ′, and the channel B power plane  276 ′. The logic power plane  270 ′ substantially overlaps with the logic ground plane  268 ′ of the ground layer embodiment shown in  FIG. 54 . The channel A power plane  274 ′ substantially overlaps with the channel A ground plane  278 ′ of the ground layer embodiment shown in  FIG. 54 . Likewise, the channel B power plane  276 ′ substantially overlaps with the channel B ground plane  282 ′ of the ground layer embodiment shown in  FIG. 54 . As can be seen, the bank  360  of diodes is located on the component layer in the area  368  positioned over the channel A power plane  274 ′. The bank  362  of diodes is positioned over the channel B power plane  276 ′. 
         [0136]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.