Abstract:
A chassis and associated telecommunication circuit card are disclosed. The chassis has heat dissipation and flame containment features while accommodating a high density of the circuitry cards. Embodiments include an inner housing with a double-layer middle floor dividing the chassis into top and bottom chambers. Each layer has partially aligned slots, and an air gap is provided between the two layers. Embodiments also include a double-layer mesh cover with an air gap existing between the two mesh layers. Projections and grooves are provided on the inner surfaces of the inner housing to receive circuit cards having a guide on one edge and a fin on another. 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 features of the chassis and includes some components chosen for low-power consumption or reduced flammability.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of the application with Ser. No. ______ entitled TELECOMMUNICATIONS CHASSIS AND CARD WITH FLAME SPREAD CONTAINMENT filed on Feb. 28, 2001. 
     
    
     
       TECHNICAL FIELD  
         [0002]    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 flame spread containment and/or high card density.  
         BACKGROUND  
         [0003]    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 while containing the spread of flames should a fire be imposed within the chassis. 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 rack that contains several other chassis stacked above and below. The heat and flames that may develop within a chassis in the rack have the potential to harm circuit cards housed in the chassis above and below the chassis where the heat and/or flames emanate from, and the flames should be contained to avoid damaging cards in the other chassis.  
           [0004]    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 and flames. 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 and flames.  
           [0005]    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 and potential flame spread, 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. Achieving effective heat dissipation with adequate flame spread and 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 and flames 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 and flames 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 and flames 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.  
           [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 flame and electromagnetic noise containment.  
         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 flame and electromagnetic noise containment features. Ventilation and containment structures are employed to direct heat away from internal circuitry while preventing flames from spreading within the chassis. Additionally, chassis designs of the present invention may provide exterior features that establish protection from externalities and prevent the harmful spread of heat and flames 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.  
           [0009]    The present invention may be viewed as a chassis for housing repeater cards. The chassis includes an inner housing with vertical sidewalls, a first surface, and a second surface. The first surface and the second surface have a first and second row of openings. The chassis also includes one or more repeater cards positioned between the first surface and the second surface. The one or more repeater cards has a DC-DC converter and a transceiver with the DC-DC converter being positioned between a first opening of the first row of the first surface and a first opening of the second row of the second surface at least partially aligned with the first opening of the first row of the first surface. The transceiver is positioned between a first opening of he second row of the first surface and a first opening of the second row of the second surface at least partially aligned with the first opening of the second row of the first surface.  
           [0010]    The present invention may also be viewed as a repeater card. The repeater card includes a printed circuit board having a ground layer and a power layer separated by a dielectric with the ground layer having a chassis ground plane, a logic ground plane, and a first channel ground plane, and with the power layer having a logic power plane and a first channel power plane. The logic ground plane substantially overlaps with the logic power plane and the first channel ground plane substantially overlaps with the first channel power plane. A DC-DC converter is mounted to the printed circuit board and electrically linked to the logic ground plane, the logic power plane, the first channel ground plane, the first channel power plane, and the chassis ground plane. A transceiver is mounted to the printed circuit board and electrically linked to the DC-DC converter, the logic ground plane, the logic power plane, the first channel ground plane, and the first channel power plane. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1A is a top front perspective view of a chassis loaded with repeater cards  
         [0012]    [0012]FIG. 1B is a bottom front perspective view of the chassis loaded with repeater cards.  
         [0013]    [0013]FIG. 2 is a top front perspective view of an empty chassis with card slot covers in place.  
         [0014]    [0014]FIG. 3A is a top view of the empty chassis.  
         [0015]    [0015]FIG. 3B is a front view of the empty chassis.  
         [0016]    [0016]FIG. 3C is a right side view of the empty chassis.  
         [0017]    [0017]FIG. 4A is a top view of the loaded chassis.  
         [0018]    [0018]FIG. 4B is a front view of the loaded chassis.  
         [0019]    [0019]FIG. 4C is a right side view of the loaded chassis.  
         [0020]    [0020]FIG. 5A is a bottom rear perspective view of the loaded chassis.  
         [0021]    [0021]FIG. 5B is a top rear perspective view of the loaded chassis.  
         [0022]    [0022]FIG. 6A is another top view of the loaded chassis.  
         [0023]    [0023]FIG. 6B is a rear view of the loaded chassis.  
         [0024]    [0024]FIG. 6C is a left side view of the loaded chassis.  
         [0025]    [0025]FIG. 7 is a side view of the empty chassis with the outer sidewall removed.  
         [0026]    [0026]FIG. 8 is an exploded top rear perspective view of the empty chassis.  
         [0027]    [0027]FIG. 9 is a top view of the empty chassis with the top cover layers and top surface of the inner housing removed.  
         [0028]    [0028]FIG. 10 is an exploded top front perspective view of the empty chassis.  
         [0029]    [0029]FIG. 11A is a top view of the empty inner housing of the empty chassis.  
         [0030]    [0030]FIG. 11B is a cross-sectional front view of the empty inner housing of the empty chassis along lines A-A of FIG. 11A.  
         [0031]    [0031]FIG. 11C is a partial top front perspective view of the empty inner housing of the empty chassis.  
         [0032]    [0032]FIG. 12 is a top front exploded perspective view of the inner housing of the chassis loaded with three cards.  
         [0033]    [0033]FIG. 13 is a bottom front exploded perspective view of the inner housing of the chassis loaded with three cards.  
         [0034]    [0034]FIG. 14 is a top rear exploded perspective view of the inner housing of the chassis loaded with three cards.  
         [0035]    [0035]FIG. 15 is a bottom rear exploded perspective view of the inner housing of the chassis loaded with three cards.  
         [0036]    [0036]FIG. 16A is a top front perspective view of the backplane of the chassis.  
         [0037]    [0037]FIG. 16B is a top view of the backplane of the chassis.  
         [0038]    [0038]FIG. 16C is a front view of the backplane of the chassis.  
         [0039]    [0039]FIG. 16D is a right side view of the backplane of the chassis.  
         [0040]    [0040]FIG. 17A is a partial top front perspective view of a card mounted to a floor surface of the inner housing of the chassis.  
         [0041]    [0041]FIG. 17B is a top rear perspective view of a card mounted to a floor surface of the inner housing of the chassis.  
         [0042]    [0042]FIG. 17C is a top front perspective view of a card mounted to a floor surface of the inner housing of the chassis.  
         [0043]    [0043]FIG. 17D is a partial top rear perspective view of a card mounted to a floor surface of the inner housing of the chassis.  
         [0044]    [0044]FIG. 18A is a partial bottom front perspective view of cards partially installed relative to a ceiling surface of the inner housing of the chassis.  
         [0045]    [0045]FIG. 18B is a partial top front perspective view of cards partially installed relative to a ceiling surface of the inner housing of the chassis.  
         [0046]    [0046]FIG. 18C is a partial bottom rear perspective view of cards partially installed relative to a ceiling surface of the inner housing of the chassis.  
         [0047]    [0047]FIG. 18D is a partial top rear perspective view of cards partially installed relative to a ceiling surface of the inner housing of the chassis.  
         [0048]    [0048]FIG. 19A is a top view of a repeater circuit card.  
         [0049]    [0049]FIG. 19B is a left side view of the repeater circuit card.  
         [0050]    [0050]FIG. 19C is a front view of the repeater circuit card.  
         [0051]    [0051]FIG. 20A is a top front perspective view of the repeater circuit card.  
         [0052]    [0052]FIG. 20B is an exploded top right perspective view of the repeater circuit card.  
         [0053]    [0053]FIG. 20C is an exploded top left perspective view of the repeater circuit card.  
         [0054]    [0054]FIG. 21 is an exploded top rear perspective view of a heat baffle.  
         [0055]    [0055]FIG. 22 is top front perspective view of a rack holding multiple chassis and the heat baffle.  
         [0056]    [0056]FIG. 23A is front view of a rack holding multiple chassis and the heat baffle.  
         [0057]    [0057]FIG. 23B is a right side view of a rack holding multiple chassis and the heat baffle.  
         [0058]    [0058]FIG. 24A is top front perspective view of a rack holding multiple chassis and the heat baffle positioned for installation.  
         [0059]    [0059]FIG. 24B is right side view of a rack holding multiple chassis and the heat baffle positioned for installation.  
         [0060]    [0060]FIG. 25 is a side view of the circuit board of the circuit card showing the relative position of the components of a repeater circuit.  
         [0061]    [0061]FIG. 26 is a schematic of alarm circuitry of the repeater circuit.  
         [0062]    [0062]FIG. 27 is a schematic of transceiver configuration circuitry of the repeater circuit.  
         [0063]    [0063]FIG. 28 is a schematic of power supply circuitry of the repeater circuit.  
         [0064]    [0064]FIG. 29 is a view of a ground conductor layer of the printed circuit board supporting the repeater circuit.  
         [0065]    [0065]FIG. 30 is a view of a power conductor layer of the printed circuit board supporting the repeater circuit.  
         [0066]    [0066]FIG. 31 is a view of a component layer of the printed circuit board supporting the repeater circuit. 
     
    
     DETAILED DESCRIPTION  
       [0067]    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.  
         [0068]    [0068]FIGS. 1A and 1B show a loaded chassis  100  in accordance with one embodiment of the present invention. The chassis includes vertical sidewalls including right sidewall  104 . A top mesh cover  102  is included, and this cover as well as other mesh covers discussed below typically are perforated rolled steel wherein the perforations provide air passages. An exemplary mesh cover is made of aluminum and has 63% of its surface occupied by relatively small and densely positioned air passages, but other materials and air passage percentages for the mesh covers are also applicable. Cover  102  may have angular portions  102 ′. As with all surfaces of the chassis  100 , the rolled steel may be used and may have a clear chromate plating to reduce electromagnetic interference. The chassis  100  also has a bottom mesh cover  116  that covers the bottom of the chassis  100 .  
         [0069]    A backplane  106  having external connectors  108  is included for establishing electrical communication between the circuit cards  110  housed by the chassis  100  and external cabling passing through the chassis rack. The external connectors  108  may be a terminal block, but other connector types are suitable as well. The cards typically have a mounting screw  110 ′ that secures the card to the chassis  100 . The chassis  100  includes mounting flanges  112  and  114  for installation of the chassis  100  in a rack. A ground connector  109  is included for providing chassis ground.  
         [0070]    FIGS.  2 - 3 C show an empty chassis  100 . The empty chassis  100  has card slot covers  111  that cover each card slot reserved for a circuit card  110 . The card slot covers are held in place by a screw  111 ′ that is secured to the chassis  100 . FIGS. 3A and 3C also show a backplane cover  118  that is more clearly shown in FIGS.  5 A and  5 B. The backplane cover  118 , typically made of lexan, prevents exposure of circuit leads and pins on the backside of the backplane  106 .  
         [0071]    FIGS.  4 A-C show a loaded chassis  100 . The loaded chassis  100  is filled with circuit cards  110  held in place by the fastener  110 ′. The circuit cards  110  have a finger  175  extending from a faceplate  174 . The finger  175  provides a handle for an operator to grip when inserting or removing the circuit cards  110  from the chassis  100 . The finger  175  and circuit card  110  are shown and described in more detail below.  
         [0072]    FIGS.  5 A- 6 C illustrate the chassis  100  with the focus shifted to the rear portion where the backplane  106 , external connectors  108 , and backplane cover  118  are located. The vertical sidewall  105  is also visible in these views. Also visible in these views is a backplane power connection  106 ′ that generally mates to a power connection in a rack to provide power to circuit cards  110  through internal connectors discussed below and receive alarm signals generated by the circuit cards  110 .  
         [0073]    [0073]FIG. 7 shows a side view of the chassis  100  with the sidewall  104  removed. As can be seen, the chassis  100  consists of several layers including the top mesh cover  102 , an air gap  103 , a second mesh cover layer  120  and  122 , a top surface  132 , a middle floor  134 , and the bottom surface  138 . The second mesh cover layer  120  and  122  overlays the top surface  132 , and the top mesh cover  102  overlays the second mesh cover layer  120  and  122 . The air gap  103  is established by ridges  130  formed in the top surface  132  that create recessed portions  131  in the top surface. Cover projections  123  are provided to maintain spacing between cover layer  102  and the underlying mesh strips  120  and  122 . The sidewalls  104 ,  105 , the middle floor  134 , and the top surface  130  and bottom surface  138  are held together by fasteners  132 ′,  142 ′,  140 ′, and  138 ′.  
         [0074]    The middle floor includes a top plate  142  and a bottom plate  140  separated by an air gap  143 . The top plate  142  overlays the bottom plate  140 . Similar to air gap  103 , ridges  158  in the bottom plate  140  create recessed portions  141  that establish the air gap  143  in the middle floor  134 . The bottom mesh cover  116  directly underlays the bottom surface  138 . The relationship of these layers relative to the inner housing  101  is further illustrated in FIG. 8.  
         [0075]    [0075]FIG. 8 shows the exploded view from a top rear perspective of the chassis  100 . The underlying mesh cover layer  120  and  122  is shown as two individual strips of mesh material. These two strips  120  and  122  lie within the recesses  131  formed in the top surface  132  between the ridges  130 . Inner sidewalls  126  within inner housing  101  are also visible in FIG. 8. These inner sidewalls  126  create compartments  125  and  127  within a bottom chamber  125 ′ and top chamber  127 ′, respectively, within the inner housing  101 . Internal connectors  124  located on the inner side of backplane  106  are also visible and are used to mate with the circuit card  110 . The airgap  143  in the middle floor  134  is also shown.  
         [0076]    [0076]FIG. 9 shows a top view of the chassis  100  with the top cover  102 , second cover layer strips  120  and  122 , and the top surface  132  of the inner housing  101  removed. The top plate  142  is visible and openings including slots  154  are visible. The bottom plate  140  is partially visible through the slots  154  where the bottom plate&#39;s slots  150  are not in perfect alignment due to shape, position, or size with the slots  154  of the top plate  142 . As described below, these slots  150  and  154  permit heat from circuit cards  110  in bottom chamber  125 ′ to be dissipated while containing flames emanating from the bottom chamber  125 ′.  
         [0077]    [0077]FIG. 10 shows an exploded view of the chassis  100  with the inner housing intact from a top front perspective. The internal connectors  124  are shown. The internal connectors fit within the compartments  125  and  127  and the circuit cards  110  slide into the inner housing  110  from the front. A connector on the circuit card  110  then slides into engagement with the internal connector  124 . Generally, one card corresponds to one internal connector  124 . As shown, seven cards fit into a single compartment  125  or  127 . Also shown in FIG. 10 are cover projections  123  on the mesh cover layer formed by the individual mesh strips  120  and  122 . The cover projections  123  assist in maintaining the air gap  103  formed between the top mesh cover  102  and the mesh strips  120 ,  122 .  
         [0078]    FIGS.  11 A- 11 C show the inner housing  101  from several views. In FIG. 1A, looking down onto the top surface  132 , a slight misalignment between the slots  154  of the top plate  142  and be seen because top plate  142  is visible through slots  160  in the top surface  132  of the inner housing  101 . As discussed above, misalignment of the slots may result from different sizes or shapes of the slots in one surface relative to those of another or may result from slots of the same size and shape not having a common position in one surface relative to the slot position in another surface. As shown, slots  144  in the bottom surface  116  and slots  154  in the top plate  142  have the same size, shape and common position and are aligned but misalignment is introduced by slots  150  in bottom plate  140  because slots  150  in the bottom plate have a different size. Similarly, slots  150  in the bottom plate and slots  160  in the top surface have the same size, shape, and common position and are aligned, but slots  154  in the top plate have a different size and therefore, introduce misalignment. This misalignment facilitates the flame containment while allowing heat dissipation to occur.  
         [0079]    [0079]FIG. 11B shows a front cross-sectional view taken through line A-A of FIG. 11A. The air gap  143  can be seen in this view. Also visible is the side-to-side alignment of openings  144  and  154  in the bottom surface  116  and the top plate  142 , respectively. The side-to-side alignment of openings  150  and  160  in the bottom plate and the top surface, respectively, can also be seen. Misalignment between openings  144  and  150 , between openings  150  and  154 , and between  154  and  160  is visible as well.  
         [0080]    [0080]FIGS. 12 through 15 show exploded views of the inner housing  101  from top front, bottom front, top rear, and bottom rear perspectives, respectively. Several circuit cards  110  are shown in installed positions relative to the top plate  142  or the bottom plate  140 . Inner side walls  126  include ribs  126 ′ that are sized to fit within ridges  130  of the top surface  132  or  158  of the bottom plate  140 . Ribs  126 ′ prevent flames from spreading over the inner sidewall  126  through the ridge  130  or  158  and into adjacent compartments and further support the middle floor  134  and the top surface  132 . Mounting tabs  138 ′ on the bottom surface  138  and mounting tabs  142 ′ on the top plate  142  extend vertically upward to contact the vertical sidewalls  126 ,  104 ,  105  and hold them in place. Similarly, mounting tabs  132 ′ on the top surface  132  and mounting tabs  140 ′ on the bottom plate extend vertically downwardly to contact the vertical sidewalls  126 ,  104 ,  105  and hold them in place.  
         [0081]    As shown, the inner housing  101  provides eight compartments including four top chambers and four bottom chambers, with each chamber holding up to seven circuit cards  110 . Thus, for the chassis  100 , the inner housing  101  shown can accommodate fifty-six circuit cards  110 . It is to be understood that the number of chambers spanning the width of chassis  100  may vary from the number shown, as may the number of chambers that span the height. Four are shown spanning the width and two are shown spanning the height only as an example. Furthermore, it is to be understood that the number of circuit cards per compartment may vary and that seven are shown only as an example.  
         [0082]    To hold each circuit card, the bottom surface  138  is provided with projections  146  shown as lances that hold guides on the circuit cards  110 . The top plate  142  of middle floor  134  also has projections  152  to hold guides on the circuit cards  110  installed above the middle floor  134 . To provide guidance for the top of the circuit cards  110  installed in the bottom chamber  125 , a bottom plate  140  of the middle floor  134  has grooves or fin slots  156  running from the front edge where the cards  110  are inserted to the back edge where the backplane  106  is located. The leading edge of the top plate  142  of middle floor  134  is also grooved or slotted to align with the grooves or fin slots  156  of the bottom plate  140 . The top surface  132  of the inner housing  101  also has grooves or fin slots  148  that provide guidance to the top of the circuit cards  110 . The separation  143  in the middle floor  134  aids in the ability to provide grooves or fin slots  156  on the bottom side while providing projections  152  on the top side.  
         [0083]    The ventilation slots  144  of the bottom surface  138  allow air passing up through the bottom mesh cover  116  to pass between the circuit cards  110  in the bottom chambers  125 . Slots  150  of the bottom plate  140  at least partially align with the slots  144  in the bottom surface  138  and air passing up between the circuit cards  110  located in the bottom chambers  125  may pass through the slots  150  in the bottom plate  140 . The top plate  142  has slots  154  that are at least partially aligned with the slots  150  of the bottom plate  140  and air passing up through the slots  150  in the bottom plate pass through the separation and then through the slots  154  in the top plate  142 .  
         [0084]    After air has passed through the middle floor  134 , it may rise between circuit cards  110  installed in the top chambers. Slots  160  of the top surface  132  allow the air to pass through the top surface  132 . The mesh cover created by the mesh strips  120  and  122  allows the air to pass into the separation between the mesh strips  120 ,  122  and the top mesh cover  102 . Air then may pass through the top meshcover  102 .  
         [0085]    Thus, air can be successfully channeled through the bottom cover  116  up through the chassis  100  and out through the top cover  102 . When chassis are stacked, air passing out the top mesh cover  102  of the lower chassis  100  passes into the next chassis  100  through the bottom mesh cover  116 . This continues until air passes out of the top mesh cover  102  of the highest stacked chassis  100 . Heat generated by the circuit cards  110  is channeled up through each chassis passing through the small separation between cards  110  until it exits out of the rack.  
         [0086]    The slots  144  may be provided in several rows on the bottom surface  138 , and three rows are shown including a first row  224 , a second row  226 , and a third row  228 . A solid area  210  on the bottom surface  138  may be included, such as between the first row  224  of slots and a first edge  234  of the bottom surface  138 . The third row  228  of slots of the bottom surface  138  may be positioned between the second row  226  of slots and a second edge  240  that is opposite the first edge  234  of the bottom surface  138 .  
         [0087]    Similarly, the slots  150  and  154  of the middle floor  134  may be positioned in several rows, such as the three-row configuration shown. The slots of first row  218  of the middle floor  134  at least partially overlap with the slots of the first row  224  of the bottom surface  138 . The slots of second row  220  of the middle floor  134  at least partially overlap with the slots of the second row  226  of the bottom surface  138 . The slots of the third row  222  at least partially overlap with the slots of the third row  228  of the bottoms surface  138 .  
         [0088]    The middle floor  134  may also include a solid area  208  that is positioned between the first row  218  of slots and a first edge  323  of the middle floor  134 . The third row  222  of slots of the middle floor  134  may be positioned between the second row  220  of slots and a second edge  238  opposite the first edge  232  of the middle floor  134 . The solid area  208  at least partially overlaps with the solid area  210  of the bottom surface  138 .  
         [0089]    The slots  160  of the top surface  132  may be positioned in several rows as well, including the three adjacent rows that are shown. The slots of the first row  212  of the top surface  132  at least partially overlap with the slots of the first row  218  of the middle floor  134 . The slots of the second row  214  of the top surface  132  at least partially overlap with the slots of the second row  220  of the middle floor  134 . The slots of the third row  216  of the top surface  132  at least partially overlap with the slots of the third row  222  of the middle floor  134 .  
         [0090]    The top surface may also include a solid area  206  that is positioned between the first row  212  of slots and a first edge  230  of the top surface  132 . The third row  216  of slots may be positioned between the second row  214  of slots and a second edge  236  of the top surface  132  opposite the first edge  230 . The solid area  206  at least partially overlaps with the solid area  208  of the middle floor  134 .  
         [0091]    The spacing between the top plate  142  and the bottom plate  140  of the middle floor  134  diffuses flames emanating from circuit cards  110  in the bottom chamber  125 ′ before they may pass into the top chamber  127 ′. Likewise, mesh strips  120 ,  122  and the separation between the mesh strips  120 ,  122  and the mesh cover  102  diffuse flames emanating from circuit cards  110  in the top chamber  127 ′. Additionally, the bottom mesh cover  116  of the next chassis up in the rack assists in diffusing any flames not fully diffused by the mesh cover layers in the top of the chassis  100 . Inner side panels  126  create barriers to flames escaping to the sides of the chambers so that the flame becomes trapped within a chamber between the two side panels  126 , the floor, and the ceiling.  
         [0092]    In the event of a fire, material on a given circuit card burns, soot is formed and rises. The soot may collect in the perforations of the mesh covers to clog the holes. This clogging effect assists in choking the fire. Furthermore, the bottom cover  116  catches material as it would fall from a burning card. The mesh strips  120 ,  122  are positioned so that they overlay the first and second rows of slots of the top surface  132 , middle floor  134 , and bottom surface  138 . Thus, the third row of slots of the top surface  132 , middle floor  134 , and bottom surface  138  are not covered by the mesh strips  120 ,  122  but only by the mesh cover  102 . As a result, a less resistive pathway is created through up through the third row and additional ventilation is provided through the third row  228 ,  222 , and  216 .  
         [0093]    The opposite effect is created by providing the solid areas of the top surface  132 , middle floor  134 , and bottom surface  138 . The overlapping solid areas  206 ,  208 , and  210  prevent upward air flow. As a result, air is channeled from the front edges  234 ,  232 , and  230  toward the third row  228 ,  222 , and  216  and eventually up through the mesh cover  102 . Electrical components, such as large capacitors that tend to burn but do not produce significant amounts of heat may be positioned between the overlapping solid areas so that less ventilation is provided across them.  
         [0094]    Electrical components that do produce significant amounts of heat may be positioned between the overlapping rows of slots so that ventilation is adequate. Electrical components that may produce heat and are susceptible to some burning may be positioned between the overlapping first rows or between the overlapping second rows so that ventilation is provided, but mesh strips  120 ,  122  provide additional flame diffusion. Layout of a repeater circuit card as it relates to the slots and solid areas of the chassis  100  is discussed below with reference to FIGS. 17A and 25.  
         [0095]    FIGS.  16 A- 16 D show the backplane. As previously discussed, the backplane  106  provides several internal connectors  124  sized to engage an electrical connector on the circuit card  110 . The connectors  124  generally provide signals to the circuit card  110  and/or receive signals from it. The connectors  124  pass signals between the card and the external connectors  108 . The external connectors are sized to engage electrical cables passing up through a chassis rack.  
         [0096]    As shown, fourteen external connectors  108  are provided and fifty-six internal connectors  124  are provided. Thus, each external connector communicates with four internal connectors  124 . A power connector  106 ′ is also located on the backplane and is sized to engage a power connector in the chassis rack. The power connector  106 ′ provides power to each of the internal connectors  124  that then channel the electrical power to the circuit card  110 .  
         [0097]    FIGS.  17 A- 17 D show several views of the repeater circuit card  110  installed relative to the bottom surface  138  of the inner housing  101  of the chassis  100 . The cards  110  mount in the same fashion to the top plate  142 . The repeater circuit card  110  has a guide  164  that is generally perpendicular to the card  110  and that fits between the projections  146  of the bottom surface  138  and the projections  152  of the middle floor  134 . The guide  164  includes slots  166  that partially align with the slots  144  in the bottom surface. Likewise, the slots  166  partially align with the slots  154  in the top plate  142  of the middle floor  134 . Thus, the air passing through the bottom surface  138  and/or through the middle floor  134  passes through the slots  166  in the guide  164  on each circuit card  110  and then between each circuit card  110  and on through the area above.  
         [0098]    As discussed above and shown in detail in FIG. 17A, electrical components such as a capacitor  242  that do not produce significant heat but are susceptible to burning may be positioned on specific locations of the card  110 . For example, the capacitor  242  may be positioned such that when the card  110  is fully installed in the chassis  100 , the component  242  is positioned between solid areas such as above the solid area  210  of the bottom surface  138  and below the solid area  208  of the middle floor  134 .  
         [0099]    Components that do produce heat such as a DC-DC converter  244  or a transceiver  246 , may be positioned on the card  110  such that when the card is fully installed in the chassis  100  the components  244 ,  246  are positioned between overlapping rows of slots. As shown, the component  244  is positioned between the first row  224  of the bottom surface  138  that overlaps with the first row  218  of the middle floor  134 . The component  246  is positioned between the second row  226  of the bottom surface  138  that overlaps with the second row  220  of the middle floor  134 . The circuitry including DC-DC converter  244  and transceiver  246  of a repeater circuit card  110  are discussed in more detail below.  
         [0100]    The circuit card  110  has a connector  168  that mates with card edge connector  124  on the backplane  106  of the chassis  100  once the card  110  has been fully inserted into a card position in the inner housing  101 . A card faceplate  174  abuts the bottom surface  138  of the inner housing  101  and may provide a connection to the middle floor  134  or top surface  132  to lock the card  110  in place. In addition to the guide  164  aligning the card  110  in conjunction with the projections  146 ,  152  within a card position in the inner housing  101 , fin  170  also assists by guiding the top of the card  110  when introduced into a groove or fin slot  148 ,  156 .  
         [0101]    FIGS.  18 A- 18 D show various views of repeater cards  110  with a position relative to grooves or fin slots  148  in recessed areas  131  defined by ridges  132  in the top surface  132  of the inner housing  101 . As the card  110  is being inserted into a card position in the inner housing  101 , the fin  170  must align with the groove  148  for the card to fit perpendicularly relative to the top surface  132 . A perpendicular orientation of the card relative to the top surface  132  is used in this embodiment for the guide  164  of the card  110  to seat on the middle floor  134 , or bottom surface  116  and fit between the guide projections  146 ,  152 . A perpendicular orientation also permits the card connector  168  to easily slide into and out of the backplane connector  124 .  
         [0102]    The card  110  is guided by the groove  148  as it is inserted, and once the guide  164  reaches a projection  146 ,  152 , the guide  164  also assists in maintaining the card  110  within a designated card position. Once the card is fully inserted, the card connector  168  maintains electrical connection to the internal backplane connector  124  and the card faceplate  174  abuts the top surface  132 .  
         [0103]    FIGS.  19 A- 19 C show various plan views and FIGS.  20 A- 20 D show various exploded views of a T 1  repeater card  110 . It is to be understood that the chassis  100  may accommodate circuit cards  110  having functionality other than that of a repeater circuit. The repeater card  110  has a main printed circuit board  172  housing various electrical circuitry  172 ′. Typically with a repeater circuit, the card  110  will include a transceiving device to receive and reconstruct a signal having a data component and a clock component. The repeater circuitry  172 ′ also usually includes amplification. This circuitry  172 ′ may generate a significant amount of heat that must be dissipated by the chassis  100 .  
         [0104]    As shown, the connector  168  received by internal backplane connector  124  is an extension of the printed circuit board  172 . The guide  164  with slots  166  that fits between the projections  146 ,  152  attaches to the bottom edge of the printed circuit board  172  and is positioned transversely relative to the circuit board  172 . The guide is typically made of sheet metal. The fin  170  that fits within the groove  148 , attaches to the top edge of the printed circuit board  172  and lies in a plane parallel to that of the printed circuit board  172 . The fin  170  is also typically made of sheet metal.  
         [0105]    Faceplate  174  attaches to a front edge of the repeater card  110 . The faceplate typically has light emitting diodes (LEDs)  177  that allow visual inspection of the circuit card&#39;s operation. As discussed, the faceplate  174  may establish a fixed connection to the middle floor  134  or the top surface  132  with fastener  110 ′ to hold the card  110  within the inner housing  101 . A generally forward positioned finger  175  extending away from the faceplate  174  in a direction opposite to the printed circuit board  172  may be integrated into the faceplate  174  to assist in the insertion and removal of the card  110  from the chassis  100 .  
         [0106]    [0106]FIG. 21 illustrates a heat baffle  177  that may be utilized by an embodiment of the present invention. The baffle  177  has a hood portion  179 . The hood portion  179  has a sloped portion  176  and triangular side panels  188 . The triangular side panels  188  have mounting flanges  190  that rest on the surface of a chassis  100 . The baffle  177  also has a base portion  181  having a floor  182  and a face  192 . The base portion  181  lies directly over the top mesh layer  102  and the hood portion  179  directly overlays the base portion  181  with the face  192  being fixed to the sloped region  176  with clips  184  that pass through slots  186  to pinch the face  192  to a lip  189  extending from the sloped region  176 . The heat baffle  177  may be utilized by inserting the baffle between chassis  100  stacked in a rack. As heat and/or flames rise from the top cover  102  of a chassis  100 , the heat and/or flames are diverted out the front or back of the rack depending upon the orientation of the baffle  177 .  
         [0107]    The hood portion  179  of the baffle  177  is typically a solid sheet of rolled sheet metal. Thus, heat and flames cannot permeate the sloped surface  176  and are redirected. However, the base portion  181  is typically a mesh material such as permeated rolled sheet metal that allows heat to pass through while diffusing flames. The hood portion is fixed to the rack holding the chassis  100  with mounting flanges  178  and  180 . The mounting flanges  178 ,  180  are shown as being mounted to a first position used where the front of the chassis  100  extends beyond a rail of the rack. Where the chassis  100  has a front edge flush with the mounting rail of the rack, the flanges  178 ,  180  attach so that they are flush with the front edge of the baffle  177 .  
         [0108]    FIGS.  22  shows a top front perspective view of a rack  194  holding several chassis  100  with a heat baffle  177  installed. The heat rises through the chassis  100  as previously discussed and exits out the top cover  102  of the top chassis and is redirected to the rear of the rack  194  by the heat baffle  177 . The typical chassis includes a base  196  with a front portion  198 . Two vertical siderails  200  and  202  are included and are fixed to the base  196 . Each chassis  100  and the heat baffle  177  slides into position between the siderails  200  and  202  and mounting flanges  112 ,  114  of the chassis  100  and the flanges  178 ,  180  of the baffle  177  abut the rails  200 ,  202 . Cable bars  204  extend from the siderails  200 ,  202  and wrap behind each chassis  100  and baffle  177 .  
         [0109]    [0109]FIGS. 23A and 23B show a front and right side view, respectively, of the rack  194  holding several chassis  100  with the heat baffle  177  installed. As shown, the heat baffle  177  is oriented with the face  192  directed to the rear of the rack  194 . The front edge of the heat baffle  177  is flush with the front edge of the chassis  100 , and the rear edge of the heat baffle  177  slightly overhangs the rear edge of the chassis  100  to prevent heat and/or flames from curling down directly into the backplane FIGS. 24A and 24B show a top front perspective view and a right side view, respectively, of the rack  194  with the baffle  177  positioned for installation. The baffle  177  slides into the rack  194  above the top-most chassis  100  and rests on the top cover  102  of the top-most chassis  100 . The flanges  178 ,  180  (shown unattached) are attached to the baffle  177  at the front edge so that when the baffle  177  is inserted into the rack, the front edge of the baffle  177  is flush with the front edge of the chassis  100  when the flanges  178 ,  180  contact the siderails  200 ,  202 , as can be seen in FIG. 22.  
         [0110]    [0110]FIG. 25 shows a side view of a repeater circuitboard  172  of a card  110  suitable for installation in the chassis  100 . The repeater circuit board  172  has several components positioned on the board  172  in relation to the solid areas, rows of slots, and mesh strips of the horizontal surfaces of the chassis  100 . The repeater circuit board  172  includes power supply capacitor  242 , DC-DC converter  244 , and transceiver  246  previously discussed. The board  172  has LEDs  262 ,  264 , and  266  that provide external visual indications of the repeater circuit&#39;s operation. Other components of the board  172  include but are not limited to relays  248 ,  250 , and  252 , a programmable logic device (PLD)  268 , multi-position switches  254  and  256 , an oscillator  286 , and isolation transformers  258 ,  258 ′,  260 , and  260 ′. These components and their functions are discussed in more detail below.  
         [0111]    The capacitor  242  is positioned such that solid areas of the chassis  100  are above and below to prevent ventilating the capacitor  242 . The solid areas direct air toward the rear of the board  172  past the DC-DC converter  244  and transceiver  246  with some air passing up through the first row and second rows of slots and the remainder passing up through the less restricted third row of slots. The DC-DC converter  244  may be a model that is highly flame resistant to further enhance the flame containment of the chassis  100 . An epoxy encased DC-DC converter  244  such as the Ericsson PFK 4611SI is suitable. A monitor jack, which might ordinarily be placed between the LEDs  264  and  266 , is absent in the embodiment shown to reduce the material on the board  172  that is susceptible to burning.  
         [0112]    [0112]FIG. 26 shows the alarm circuitry  271  of the repeater circuit board  172 . The alarm circuitry  271  controls the LEDs  262 ,  264 , and  266 . During normal operation, the LEDs  262 ,  264 , and  266  are one color, such as green, to indicate normal operation. The power LED  262  turns red if the logic power plane  272  loses voltage from the output of the DC-DC converter  244 . This occurs due to relay  252  changing state in response to the loss of logic power thereby causing voltage received directly from the backplane connector  168  to activate the red diode of LED  262  instead of the green diode.  
         [0113]    The channel A LED  264  and channel B LED  266  are electrically connected to the PLD  268  and to a logic ground plane  270 . The PLD  268  receives power from the logic power plane  272  and receives control signals from the transceiver  246 . When a channel is operating normally, the PLD  268  causes the green diode of the LED to illuminate.  
         [0114]    If the transceiver  246  detects that channel A has no signal, then LOS0 line passing from the transceiver  246  to the PLD  268  is triggered causing the PLD  268  to light the red diode along with the green diode of LED  264  to create a yellow illumination. If the transceiver  246  detects that channel B has no signal, then LOS1 line passing from the transceiver  246  to the PLD  268  is triggered causing the PLD  268  to light the red diode along with the green diode of LED  266  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  168  by relay  250  changing state due to a control signal from the PLD  268 . The minor alarm line is electrically linked to a chassis ground plane  274 .  
         [0115]    If the transceiver  246  detects that it has failed, then the DFM line passing from the transceiver  246  to the PLD  268  is triggered causing the PLD  268  to light the red diode and turn off the green diode of LEDs  264  and  266  to create a red illumination. A major alarm signal is also generated and provided through the backplane connector  168  by relay  248  changing state due to a control signal from the PLD  268 . The major alarm line is electrically linked to the chassis ground plane  274  as well with coupling capacitors.  
         [0116]    The PLD  268  and relays  248 ,  250 , and  252  may be selected so as to minimize power consumption and reduce the amount of heat being generated by each circuit board  172  in the chassis  100 . The Atmel model ATF16V8BQL PLD draws only 100 milliwatts when active and is a suitable PLD for controlling the relays  248  and  250  and LEDs  264  and  266 . The NAIS TX-S relay draws only 20 milliwatts when active and is a suitable relay for controlling the LED  262  and the major and minor alarm signals.  
         [0117]    [0117]FIG. 27 shows the transceiver circuitry located on the board  172 . The transceiver  246 , such as the Level One model LXT332, is electrically connected to the logic power plane  272  and the logic ground plane  270 . The transceiver is also electrically linked to a channel A power plane  276 , a channel A ground plane  280 , a channel B power plane  278 , and a channel B ground plane  282 . Each channel has its own power and ground plane to avoid cross-talk and to avoid electrical noise from the power supply circuit of FIG. 28 and chassis  100 .  
         [0118]    The transceiver  246  is electrically linked to an oscillator  286  that is electrically connected to the logic power plane  272  and logic ground plane  270 . The oscillator  286  provides a reference frequency signal to the transceiver  246 . The transceiver  246  is also electrically connected to two multi-position switches  254  and  256 . Each multi-position switch controls the line build-out function of the transceiver  246  for one of the channels.  
         [0119]    The multi-position switch  254 ,  256  may be user adjusted to provide a connection between the logic power plane  272  and various pins of the transceiver  246 . The transceiver  246  then determines the signal level and signal shape for the output signal of a channel based on which pins receive the logic power plane voltage. The signal level and signal shape varies depending upon the length of cable used to carry the output signal. The longer the cable, the stronger the output signal and the more its shape is altered from the shape desired at the other end of the output signal cable. For example, if a square wave is desired at the other end, then as cable length increases the output signal must have more overshoot and a greater amplitude due to the cable&#39;s impedance attenuating and rounding-off the signal.  
         [0120]    The transceiver  246  receives its input signals for each channel from the backplane connector  168  through an isolation transformer. Channel A input signal passes through isolation transformer  260 , and channel A output signal passes through isolation transformer  260 ′. Channel B input signal passes through isolation transformer  258 , and channel B output signal passes through isolation transformer  258 ′. As shown in FIG. 25, the input isolation transformer  260  and output isolation transformer  260 ′ of channel A are contained in one unit. Similarly, the input isolation transformer  258  and output isolation transformer  258 ′ of channel B are contained in another unit.  
         [0121]    [0121]FIG. 28 shows the power supply circuitry. The backplane connector  168  receives −48V DC power and provides it through the board  172  to the DC-DC converter  244 . The −48V line and the −48 V return line are linked by the capacitor  242  to eliminate ripple. These lines are also coupled to the chassis ground plane  274 . The DC-DC converter  244  outputs a voltage that is electrically connected to the logic power plane  272 , the channel A power plane  276 , and the channel B power plane  278 . The DC-DC converter  244  has a return that is electrically connected to the logic ground plane  270 , the channel A ground plane  280 , and the channel B ground plane  282 . Ferrite beads are used to isolate each power plane connected to the DC-DC converter  244  and each power plane is AC coupled to each ground plane.  
         [0122]    [0122]FIG. 29 shows a ground layer of the circuit board  172 . The ground layer includes the chassis ground plane  274  that extends around the periphery  288  of the circuit board  172  and is electrically connected to the chassis ground provided through the chassis ground connector  109  of the chassis  100 . The chassis ground plane  274  surrounds the logic ground plane  270 , the channel A ground plane  280 , and the channel B ground plane  282 . The chassis ground plane  274 , logic ground plane  270 , channel A ground plane  280 , 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  172 .  
         [0123]    [0123]FIG. 30 shows a power layer of the circuit board  172  that is adjacent to the ground layer and separated from it by a dielectric layer. The power layer includes the logic power plane  272 , the channel A power plane  276 , and the channel B power plane  278 . The logic power plane  272  substantially overlaps with the logic ground plane  270  of the ground layer. The channel A power plane  276  substantially overlaps with the channel A ground plane  280 . Likewise, the channel B power plane  278  substantially overlaps with the channel B ground plane  282 . This arrangement minimizes electrical noise and cross-talk.  
         [0124]    [0124]FIG. 31 shows a component layer of the circuit board  172 . The electrical components previously discussed are typically mounted to the component layer. The transceiver  246  is mounted in transceiver area  294 . The isolation transformers  258 ,  258 ′,  260 , and  260 ′ 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.  
         [0125]    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  274 . The metal faceplate  174  of the circuit card  110  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  174 . This metal-to-metal contact maintains the faceplate  174  at chassis ground.  
         [0126]    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.