Abstract:
A mounting arrangement for an external connection to an electrical circuit of use in a remotely mountable weatherproof bi-directional, half-duplex switching amplifier system is designed to provide maximum range for low power half-duplex radios such as Spread Spectrum radio transceivers in which a coaxial connector protrudes through the wall of a housing and is in an abutting relationship with a circuit board on which an electrical circuit is mounted.

Description:
CLAIM OF PRIORTY AND CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of and claims priority to and incorporates by reference, in its entirety, U.S. application Ser. No. 09/505,201, titled “Bi Directional Switched RF Amplifier, Waterproof Housing, Electrostatic Overvoltage Protection Device, and Mounting Bracket Therefor”, filed Feb. 16, 2000 and is a Conversion of Provisional Application Ser. No. 60/120,639, filed Feb. 18, 1999  
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention is a result of the proliferation of low power, Spread Spectrum radio modem devices in the 902-928 MHz, 2.4 GHz and 5.7 GHz bands. Popularity of these radio devices is largely due to FCC regulations that allow appropriately certified radio transceivers to be operated license free. This certification requirement restricts the transmitter output power in order to enable many users to share the band. Further, since the radios are Spread Spectrum devices, they can generally tolerate interference from other radios transmitting in the same geographical area.  
         [0003]     Many of these prior art devices were designed and intended for short range operation (less than 1000 feet, for example, due to the low transmit power restrictions and the requirement of unobstructed line-ofsite between antennas for maximum range). However, if external outdoor gain antennas are placed on tall buildings or radio towers, considerable line-of-site ranges (measured in miles) are possible. The problem here is that the losses in the typical, inexpensive coaxial transmission line between the radio and the antenna at these frequencies can be excessive unless prohibitively expensive cable is used. Putting an antenna on a tall radio tower or building would give clear line of sight to many locations, but this is largely defeated by the transmission cable loss.  
         [0004]     In a typical RF bi-directional amplifier application, a duplex amplifier with heavy filtering, such as in U.S. Pat. No. 5,502,715 to Penny, is used. However, this is in general unsatisfactory due to the fact that not only are both transmit and receive amplifiers are on at all times, thus leading to wasteful power usage, but also heavy filtering is also necessary to keep the transmit and receive signals from interfering with each other, leading to further expense and power wastage. Still further, since each transmit and receive signal must be put to a separate frequency to avoid interference, this design is wasteful of spectrum bandwidth, a scarce commodity in many applications.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the invention disclosed herein to overcome these problems and provide a telecommunications system for ranges up to 60 miles point-to-point while keeping the radiated power compliant with the certification regulations.  
         [0006]     It is also an object of the invention to provide an improved arrangement for amplification of transmit and receive radio signals. More specifically, the invention discloses the means to locate a half-duplex, switching bi-directional amplifier close to the antenna.  
         [0007]     It is also an object of the invention to provide such an RF amplifier with an improved waterproof housing enclosure for protection against water accumulation.  
         [0008]     It is still further an object of the invention to provide a universal mounting V bolt mounting bracket for the waterproof housing enclosure.  
         [0009]     It is still further an object of the invention to provide for an improved mounting arrangement for the internal printed circuit boards directly to the housing cover to provide for minimum VSWR from the coaxial connectors to the PC board strip line traces.  
         [0010]     It is still further an object of the invention to provide temperature compensated RF level sensing circuitry to permit reliable operation over a very wide temperature range.  
         [0011]     It is still further an object of the invention to provide LED indicators on the DC injector circuitry to show the operational status of the remote bi-directional switching amplifier by monitoring the current drawn by this remote bi-directional switching amplifier.  
         [0012]     It is still a further object of the invention to provide a solid state switch for switching between the transmit (TX) and the receive (RX) modes of the remote bi-directional switching amplifier.  
         [0013]     It is still a further object of the invention to provide for an electrostatic overvoltage discharge protection device, in one embodiment at the antenna port in the remote bi-directional switched amplifier circuit board, and in another embodiment as a separate component for generalized radio frequency use.  
         [0014]     Additional objects, features, and advantages of the various aspects of the present invention will become apparent from the following description of the preferred embodiments, which description should-be taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a typical installation diagram-with the bi-directional switching amplifier in conjunction with the related elements for a telecommunications system.  
         [0016]      FIG. 2  shows how the DC power is inserted into the transmission line to the remote mounted amplifier module through the DC injector circuitry.  
         [0017]      FIG. 3  shows the functional block diagram of the bi-directional switching amplifier module.  
         [0018]      FIG. 4A  shows the details of the preferred electrostatic overvoltage discharge protection device used in a circuit board environment such as at the antenna connector on the bi-directional switching amplifier module.  
         [0019]      FIG. 4B  shows the details of the preferred electrostatic overvoltage discharge protection device in a separate component form.  
         [0020]      FIG. 5  shows the details of a preferred RF sensing circuit used in the remote bi-directional switching amplifier to enable it to switch from the receive to the transmit mode of operation.  
         [0021]      FIGS. 6A and 6B  show the PC board mounted on the housing cover of the bi-directional switching amplifier module or of the DC injector in isometric and side view, respectively.  
         [0022]      FIG. 7  show an isometric view of a preferred bi-directional switching amplifier housing mounting arrangement.  
         [0023]      FIGS. 8A, 8B , and  8 C show various views of a preferred universal mounting L-member.  
         [0024]      FIGS. 9A, 9B , and  9 C show various views of a preferred implementation of the universal channel bracket to hold the L-bracket against the mounting mast.  
         [0025]      FIG. 9D  shows a preferred implementation of the V-bolt used with the universal channel bracket to hold the L-bracket against the mounting mast. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]      FIG. 1  show the remote bi-directional switching amplifier telecommunications system in a preferred typical installation. The bi-directional amplifier  1 , inside the housing enclosure  94 ; the DC power input to the housing enclosure  94  from the DC power injector  2  supplied through connection  20 , connection between the bi-directional switching amplifier I at  29  to the antenna  87  is made through a short length of inexpensive connecting cable  3  and the L-bracket  93  in conjunction with the mast  92  are the primary preferred components of the remote part of the system. The secondary components include a transmission line  4  connected to the housing enclosure  94  at  20 , a DC Power Injector  2  preferably located remote from the bi-directional switching amplifier I housing  94 , a DC Power Supply  5  which can be either DC or AC line operated, a radio transbeiver  6 , an appropriate computer, router or terminal device  7 , and connecting cables between the various elements, such as  9  between the DC power injector and the radio transceiver. The connecting cables can be varied in type so long as they are compatible with the system. The object of the invention is to use inexpensive, easily available cables wherever possible.  
         [0027]     The bi-directional switching amplifier I is mounted physically close to the antenna and is preferably, but not necessarily, outdoors. It boosts the low power transmit, TX, signal from the radio transceiver  6  to provide the full transmit output power right at the antenna per Se. It also contains a low noise amplifier (LNA) to pre-amplify the received signal when in receive mode, RX, which overcomes the loss in transmission line  4  to the radio transceiver  6 . The bi-directional switching amplifier module I has an RF (radio frequency) sensing circuit to automatically switch from the receive RX mode to the transmit TX mode when the transceiver radio  6  goes into transmit, TX. The details of this bi-directional switching amplifier I are shown in  FIG. 3  and described in detail below.  
         [0028]     The DC power injector  2  passes the RF signal through it transparently, and injects a DC voltage onto the transmission line  4  to provide DC power to the remotely mounted bi-directional switching amplifier I in lousing  94 . The DC power injector  2 , as at  FIG. 2 , has LEDs to indicate when the externally mounted remote bi-directional switching amplifier is in receive, RX, or transmit, TX, modes for operator monitoring.  
         [0029]     One of the preferred features of the invention is the bi-directional switching amplifier module I in housing  94  mounting arrangement and hardware associated with it. This mounting arrangement ensures that the bi-directional switching amplifier housing enclosure  94  is installed with the coax connectors  64  mounted to the cover  62  are facing in a downward direction. This mounting arrangement prevents water accumulation and migration into the housing enclosure  94 . This mounting arrangement, in one embodiment, preferably also features a special design “V” bolt  90  that enables the preferred L-bracket  93  in conjunction with the preferred universal channel bracket  91  to be mounted on pole or mast  92  with diameters from ½″ to over 3″, thus providing for a universal mounting. This completed preferred mounting arrangement is shown at  FIG. 7 . A specific drawing for each piece is shown at  FIGS. 8A  to  9 D.  
       The DC Power Injector  
       [0030]     Referring again to  FIG. 2 , the DC power injector  2  gets DC power from the DC power source  5  through connector  67  and inserts the DC current to the hot lead  72  of the coax connector that connects to the transmission cable through power resistor  66  and choke  63  in order to power the bi-directional switching amplifier electronics. LED indicators  70 ,  71  are provided to show to the operator that DC power is applied and when the bi-directional switching amplifier module I switches into the transmit mode, TX. The DC power injector  2  also provides the necessary DC blocking to radio transceiver  6  through connector  60  with capacitor  61 .  
         [0031]     As seen by refering to the figures, the radio transceiver  6  is connected to the DC power injector  2  via a coax cable  9  at the input connector  60 ,  64  preferably to a 50-ohm stripline  63  on the PC board  61 .  
         [0032]     The RF signal to and from the radio transceiver  6  is coupled to the output connector  72  via a blocking capacitor  61  which keeps the DC voltage from going into the radio transceiver  6 . DC voltage is injected onto the bi-directional switching amplifier side of this coupling capacitor  61  from a jack or plug  67  through an RF choke  63  and a power resistor  66 .  
         [0033]     The DC voltage drop across the power resistor  66  is a measure of the current drawn by bi-directional switching amplifier I module. Differential voltage comparator circuitry  68  compares this voltage drop to a predetermined level. If the current is less then this predetermined level, the comparator circuitry  68  illuminates the green Receive (RX) LED  71 .  
         [0034]     If the current is greater then this predetermined level, the comparator circuitry  68  illuminates the red Transmit (TX) LED  70 .  
       The Bi-directional Switched Amplifier Module  
       [0035]     The bi-directional switched amplifier module I circuitry is housed in a watertight enclosure housing  94  physically mounted adjacent to the antenna  87 . Hereinafter, the terms “enclosure” and “housing” will be used interchangeably. As shown in  FIG. 3 , the bi-directional switched amplifier I gets its DC power from the coax transmission line  4  connected to it at the input coax connector  20 . The DC power is siphoned off and the RF signal is capacitively coupled to the RF radio transceiver switch  21 . Normally the bi-directional switching amplifier I is in the Receive (RX) mode as  FIG. 3  illustrates. In this mode, RF signals from the antenna port connection  29  are passed through the RF antenna switch  22 , through the optional bandpass filter  27  and amplified by the RX LNA  26 . To reduce the signal and noise coming out of the amplifier, an optional attenuator pad  31  can be installed.  
         [0036]     When the radio transceiver  6  connected to the DC injector  2  goes into the transmit mode, the TX power is detected by the sense circuitry  24  and switches both the switch  21  from the radio transceiver and the switch  22  to the antenna to the TX position. The power sense circuitry  24  also applies DC power to the transmitter power amplifier  25  and removes power from the RX LNA  26 . In this mode, the RF signal from the radio transceiver  6  can be passed through the optional RF attenuator pad  23 , into the transmitter TX power amplifier  25  and to the antenna port  29  via the antenna RF antenna switch  22 . When the radio drops out of transmit, the TX power sense circuitry switches the RF switches  21 ,  22  back to the receive RX mode, removes power from the transmitter power amplifier  25  and turns the receive RX LNA  26  back on.  
       Electrostatic Overvoltage Protection Device  
       [0037]     Another aspect of the invention is an improved electrostatic overvoltage protection device, or “lightning arrester.” Here it has been discovered that a conductor of one-quarter the desired wavelength of a predetermined frequency band connected between a source of signal and a reference potential, such as ground, will have almost no effect on the desired signal band and signal transmission but will shunt virtually all frequencies outside this predetermined frequency band to a reference potential such as ground, thus protecting the integrity of any electronic component connected to the signal input.  
         [0038]     In a first preferred embodiment, the electrostatic overvoltage protection for an electronic circuit in a circuit board environment, such as the bi-directional switching amplifier, is shown in  FIG. 4A . This protector can protect against lightning, electrostatic charge from the environment, an Electro Magnetic Pulse (“EMP”), and any other source of static or transient overvoltage. The coax connector  29  that connects to the antenna in a preferred embodiment has a loop of heavy gauge conductor  91  of a length equal to one-quarter of the wavelength of the desired RF operational band connected from the signal input  92  of connector  29  to a source of reference potential, such as ground  93  on the PC board, thus forming an RF choke to that desired frequency band at the input and a direct ground to all other frequencies. This conductor  91  may also be a trace on the PC board or any other convenient means of forming an equivalent one-quarter wavelength conductor such that it shorts the center pin  92  directly to a reference potential such as ground  93  on the PC board for all frequencies outside the desired frequency band. This RF shunt choke is has a negligible effect on the desired RF band signal passing through the amplifier. However, any stray DC, lightning, or other electrostatic overvoltage fault at the input pin  92  of the antenna connector  29  finds this loop a very low impedance to ground (provided that the mast or pole is properly grounded) and shunts the current through it to this ground, thereby protecting the electronic circuit board, such as the bi-directional switching amplifier  1 .  
         [0039]     A second embodiment of the electrostatic overvoltage protection device is in a separate component form with both the internal and external details are shown at  FIG. 4B . The protection device, or arrester, is constructed of a T-connector housing  100  with input connection  101  and output connection  102 . The input  101  and output  102  are bi-directional and may be interchanged. A pass-through conductor  103  connects the input  101  and output  102 , and conductor  103  is surrounded by a suitable dielectric material  112  which is inside of the body housing  100 . The dielectric material  112  may also be air or a material such as rexolite, delrin, teflon or other non-conductor suitable for the radio frequency band intended. The dielectric material  112  may be a combination of air and other non-conducting materials.  
         [0040]     Here the one-quarter wavelength protector of the desired frequency band, taking into account the dielectric constant of the dielectric material  112 , is conductor  104  which connects to the through conductor  103  at one end, and to a grounding or shorting member to the outside housing at the other end. One manner of achieving this shorting to the outside Tconnector housing  100  is shown here through a ground pin such as  105  on the ground end. Here the ground pin  105  extends through an end cap  106  and thus forms an effective short to the external protector housing  100  for the conductor  104 . The connector-protection device  100  can then be put to a source of reference potential such as ground by any convenient manner. In one preferred embodiment, the ground pin  105  extends beyond the housing  100  to form a suitable ground screw  110 . As above, the total length of the conductor  104  and ground pin  105  is one quarter wavelength, ?J4, length  108  (or any odd multiple of one quarter wavelength) of the desired operating frequency as measured from the pass-through conductor  103  to the end cap assembly  106 . As above, this presents a short circuit to direct currents (DC) and any non-desired frequency and a high impedance only to the desired operating frequency band. The assembly of conductor  104 , ground pin  105 , end cap  106 , and ground screw  110  may be constructed as one continuous piece, if desired.  
         [0041]     The end cap  106  can attach to the main body of the arrester  100  by either an internal or external thread  107  (male or female connection) or any other suitable means of connection. In one simple preferred embodiment the ground screw  110  which passes through the end cap  106  is used for the attachment of a grounding conductor III, which can be a combination lug and/or braid, and held in place by nut  109 . The ground screw  110  may be of any length and is preferably highly conductive. Washers or other appropriate mounting hardware may be used between conductor III, end cap  106  and nut  109 . Ground conductor III may also be attached to end cap  106  by soldering, riveting, welding or any other method.  
         [0042]     Still further, the shorting of conductor  104  to the housing  100  at the ground end can be done by any other convenient means such as a copper foil, a highly conductive plate soldered, brazed, or welded in place, or any other conductor connection between the distal end of conductor  104  and the housing  100  in place of this end cap  106 , which is only one convenient manner of providing this connection, and a threaded member is not necessary, but useful in some situations to tune the desired band.  
         [0043]     This separate component protection device of  FIG. 4B  can have an entire range of other uses other than as an antenna protector, for instance such as protecting signals between computers or other communications devices, protection of control signals to power equipment, or any kind of networking where there may be some kind of electrostatic or transient overvoltage fault condition in a radio frequency path of a particular predetermined frequency band connection.  
       The RF Power Sense Circuitry  
       [0044]     The RF Power Sense Circuitry  24  best seen in  FIG. 5 , needs to detect low level RF signals and work in hostile outdoor environments. It is vital that the bi-directional switching amplifier module I quickly and reliably detect the presence of a transmitted signal from the radio transceiver  6  under all temperature ranges in order to switch from the Receive RX to the Transmit TX mode. The present invention utilizes a solid state circuit that senses and detects the presence of radio frequency energy (RF) and provides a digital output signal when said Transmit TX RF signal is present. The sensing circuitry  24  utilizes detection diodes  40 ,  40 ′ that are forward biased to almost the point of conduction to provide for maximum sensitivity and reliable detection for signal levels as low as 1 milliwatt. The biasing circuitry for these diodes are temperature compensated with a temperature-controlled resistor (thermistor)  39  to ensure consistent performance over a wide temperature range.  
         [0045]     Referring to  FIG. 5 , RF energy from the bi-directional switching amplifier I input connector  20  is coupled via a capacitor  41  to the junction of the preferred low capacitance Schottky dual diodes  40 ,  40 ′ in series. While any suitable diodes can be used, these have been found to be cost effective, reliable components well suited for this application. These diodes  40 ,  40 ′ combined with capacitors  42 ,  45  form a voltage doubling circuit to rectify and detect an RF signal on the input connector  20 . The resulting rectified signal is applied to an input  58  of a comparator  53 .  
         [0046]     To provide for maximum sensitivity, diodes  40 ,  40 ′ are forward biased to just below the conduction point via a 5 volt regulated source  59  through the biasing resistors  43 ,  44 , and  46 . However, since the transconductance of the diodes  40 ,  40 ′ change greatly with temperature, a thermistor  39  is added to the circuit. This thermistor  39  adjusts the current flow through the diodes  40 ,  40 ′ to provide a relatively uniform RF signal level detection point over a very wide temperature range.  
         [0047]     The trip point for the circuitry is set by the voltage reference source  50 . When the DC voltage present on input  58  exceeds the pre-set DC level on input  57 , the comparator  53  changes state indicating that an RF signal is present at the input connector  20 . The output  56  of this comparator  53  goes low. A second comparator  55  inverts this signal and provides a complementary logical high output at  54  for use by the RF switching and other circuitry in the bi-directional switching amplifier module.  
       The Preferred Mounting Arrangement for the Bi-Directional Amplifier Module  
       [0048]     Waterproof enclosures, even if mounted properly, can ultimately have a water leak when mounted outdoors through the coaxial connectors that penetrate its surface. The present invention discloses a preferred arrangement to mount such a waterproof enclosure or housing  94  containing the bi-directional switching amplifier module  1  outdoors especially to a pole or mast  92  mounted physically close to the radio antenna  87 . The antenna  87  can be at any adjacent position to the enclosure housing  94 , i.e. above the enclosure, at the same height, or below the enclosure. In the preferred embodiment, the mounting of the enclosure  94  for the bi-directional switching amplifier I has the connectors facing in a downward direction. Especially when used with drip loops, this mounting arrangement results in water being drawn away by gravity from the waterproof enclosure  94  and the external connections rather then giving it a direct path to enter such as would be the case if the connectors  20 ,  29  were installed on any other face of the enclosure  94 . The connection to the antenna  87  is also preferred to be in a downward position to minimize water migration into the connecting cable  3 .  
         [0049]     Further, conventional U-bolts mounting means or any other conventional structure for adjustably mounting the antenna  87  and housing  94  can be used with the invention. Conventional U-bolts and round masts  92  would be particularly useful in a new installation of many units where all the mounting means would be the same. However, in retrofit installations U-bolts only lend themselves to mountings on a very limited range of pole or mast diameters. Thus while U-bolts can be used with the invention, a preferred new and improved universal mounting means overcomes problems associated with these limitations by enabling installers to use a wide range of masts or poles  92  to mount the waterproof enclosure  94  and antenna  87 . A new mounting bracket  93  and V-bolt design  90  such as described herein enables the amplifier enclosure  94  to be mounted on any diameter mast or pole  92  from ½″ to over 3″ diameter. Thus during field installations, and especially retro-fit installations, an installer would not have to locate a mast or pole of particular diameter to accommodate the limited range the diameter of standard U-bolts mounting arrangements, but could bolt the mounting hardware to just about anything in this universal arrangement.  
         [0050]     This preferred universal mounting arrangement is shown in FIGS.  7 ,  8 A- 8 C, ancf 9 A- 9 D. It comprises the V-bolt  90 , a stepped channel piece  91  for the V-bolt and pole  92  to work against, L-bracket  93  to secure the channel piece  91  to the bi-directional switching amplifier module housing  94  and the nuts and washers  95  needed to hold the Vbolt  90  against the back of the L-bracket  93 . Thus the bi-directional switching amplifier module housing  94  is secured as designed with the connectors  20 ,  29  facing downward. As seen in  FIG. 7 , the L-bracket  93  provides convenient mounting for the amplifier housing  94  to the V bolt  90  as well as providing additional weather protection as a roof-covering.  
       Description of Preferred the PC Board Mounting Arrangement  
       [0051]     The Printed Circuit (PC) boards  61  containing the electronic circuitry for the bi-directional switching amplifier module I and DC power injector  2  are preferably mounted to the top cover or lid  62  of their respective enclosures. This permits the coax connectors  64  to be mounted directly to the PC board  61 , which provides for the best impedance match from these connectors to the PC board  61 , with the PC board  61  traces  63  acting as strip lines to the circuitry on the board.  
         [0052]      FIGS. 6A and 6B  show how the PC board  61  is preferably˜typically mounted to the top cover or lid  62  of the enclosure. The coax connectors  64 , for example N-female type, protrude through holes on the top of the cover  62 . The flange  64 ′ of connector  64  is sandwiched between the inside of the top cover  62  and the ground plane bottom of the PC board  61 . The flange  64 ′ of the connector  64  is fastened between the top of the cover  62  and the bottom PC board  61  using appropriate machine screws  97  and nuts  98  or any other fastening scheme intended by the manufacturer of the connector  64 . The center pin  92  of the connector is soldered or otherwise electrically connected directly through to the PC board  61  to trace  63 , which forms a preferably 50-ohm stripline to the rest of the RF circuitry. The ground connection to the PC board is secured through four mounting screws  97  or other equivalent fastening means. This presents the lowest VSWR to the transmission line connected to the device on  61  through the connector  64  and provides for the least possible loss.  
         [0053]     A highly efficient RF bi-directional switching amplifier, housing, universal mounting and electrostatic overvoltage protection means are disclosed for a modern telecommunications system. Thus by using the disclosure and teachings of the invention, any practitioner in the art is enabled to make and use the invention.