Abstract:
A portable test apparatus for conducting a plurality of tests on a communications device is provided. The unit can include a control panel, which can include at least one display for displaying test information from the device under test. The apparatus can also include a frequency mixing assembly, an amplifier module, a voltage regulator module, and a frequency module. The apparatus can allow a user to measure a number of parameters including, but not limited to, power, return loss and passive intermodulation products.

Description:
BACKGROUND 
     The present disclosure relates generally to radio frequency communication systems. In particular although not exclusively the present disclosure relates to an apparatus for measuring sources of interference. 
     Quality of Service (QOS) is of major importance to today&#39;s communication network providers. One of the major factors effecting QOS in most modern communication is interference. The two most appreciable forms of interference present in most communication systems result from Active and Passive intermodulation. In each case multiple transmitting frequencies combine in ways that cause interference to receiving equipment. 
     In the case of Active Intermodulation (AIM) interference the transmitter or receiver actively amplify interfering signals in the environment that cause harmful interference. Passive Intermodulation (PIM) interference is similar to active intermodulation interference except that it almost occurs exclusively in passive elements when two or more frequencies are simultaneously present. When signals F 1  and F 2  for example encounter a non-linear device they combine as follows, mF1±nF2, (m,n=1,2,3 . . . ) to produce interfering signals. 
     To date most suppliers of RF communications components have not been able to model PIM. One can only design components to reduce the possibility of significant levels of PIM being internally generated. Typically this reduction is achieved by applying lessons learnt from past experiences, and from testing the component presently under design. While it is possible to take account for PIM produced by each individual component during the system design phase, the effects of PIM which can be generated outside the components via poor interconnects etc, and when the component are installed on-site cannot be so easily accounted for. 
     Presently it has been relatively difficult to test for PIM on-site. Historically the equipment required to perform the testing was rather large and cumbersome and not readily suited for in-field deployment and has been widely considered by most in the communications industry as being impractical. Typically such on-site PIM testing requires each junction, line and interconnect to be checked. Without a PIM tester on-site, this operation is extremely labour intensive, requiring a technician to physically check/remake each connection as installed, and as such is extremely costly. 
     SUMMARY 
     It would be advantageous to provide a device which allows for the on-site analysis of PIM interference along with other communication system parameters in a single unit and that it performs such testing in an efficient and cost effective manner. 
     Accordingly in embodiment of the present disclosure, there is provided a portable test apparatus for a communications device, said apparatus comprising at least one display for displaying resultant values of one or more operating parameters of said communications device and a plurality of electronic modules, at least one of which is adapted to measure one or more operating parameters of said communications device, wherein said electronic modules are arranged in a substantially vertical relation. 
     In another embodiment of the present disclosure, there is provided a portable test apparatus for a communications device, said apparatus, comprising a control panel and at least one display for displaying test information from the device under test; at least one filter module assembly; at least one amplifier module; at least one voltage regulator module; and at least one frequency module; wherein said at least one amplifier module; voltage regulator module and one frequency module are stacked in vertical relation. 
     Suitably where the modules are stacked in vertical relation, they are stacked linearly on top of one another. 
     In yet another embodiment there is provided a portable test apparatus for a communications device said apparatus comprising a control panel comprising at least one display for displaying test information from the communications device; at least one filter module assembly; at least one amplifier module; at least one voltage regulator module; at least one frequency module; wherein said at least one amplifier, voltage regulator and frequency module are in a stacked configuration relative to one another. 
     In a further embodiment there is provided a portable test apparatus for a communications device said apparatus comprising a control panel comprising at least one display for displaying test information from the communications device; at least one filter module assembly; at least one amplifier module; at least one voltage regulator module; at least one frequency module; and a base plate; wherein said at least one amplifier, voltage regulator and frequency module are in a vertically stacked array between said control panel and said base plate. 
     The test apparatus may include at least one port for the connection of a device under test. The test apparatus may include at least one port as access to a built in low PIM load. Preferably the load is a cable load housed within the test apparatus. 
     Suitably the apparatus provides a plurality of selectable test modes including but not limited to a power test mode, a return loss test mode and a passive intermodulation test mode. At least one audible tone may be provided in the return loss and passive intermodulation test modes. Preferably the test apparatus includes at least two preset frequency tones, selected from the radio communication frequency bands the preset frequencies being consistent with operating frequency band license allocations. For example the present tones could be selected from a frequency range of about 800 MHz to 1000 MHz or from about 1700 MHz to 2200 MHz. It will of course be appreciated by those skilled in the art that the present tones could be set to any desired frequency by tuning the appropriate frequency generators. 
     The display may include a LED level or an LCD level display associated with a plurality of calibrated scales wherein each of the plurality of scales is associated with a test mode. 
     The apparatus may include at least one port for the attachment of an auxiliary device. 
     The auxiliary device may be a spectrum analyser, a portable computer or the like. Suitably the apparatus may include at least one port for the attachment of an auxiliary device and an I/O port for the attachment of a portable computer or the like. 
     The filter module may include a triplexer, at least one forward coupler and at least one reverse coupler. The amplifier module preferably includes at least one high power amplifier circuit. Suitably the amplifier module may include first high power amplifier circuit and second high power amplifier circuit in a parallel arrangement. Preferably the voltage regulator provides a plurality of DC voltage rails including at least one +5V rail, at least one +12V rail and at least one +26V rail. 
     The frequency module may include at least one frequency synthesiser, at least one log detector and at least one down converter circuit; at least one low noise amplifier and at least one voltage Standing Wave Ratio (VSWRi) monitor. Preferably the frequency module may include a first frequency synthesiser, a second frequency synthesiser, and a third frequency synthesiser. Suitably the first and second frequency synthesisers are adapted to produce a frequency between 800 MHz and 1000 MHz and the third frequency synthesiser is adapted to produce a frequency of approximately 50 MHz. 
     Throughout the specification the term “comprising” shall be understood to have a broad meaning similar to the term “including” and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the term “comprising” such as “comprise” and “comprises”. 
    
    
     
       BRIEF DETAILS OF THE DRAWINGS 
       In order that this disclosure may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, which illustrate preferred embodiments, and wherein: 
         FIG. 1  is an exploded view of the mounting arrangement of the test apparatus according to one embodiment of the present disclosure; 
         FIG. 2  is an exploded view of the test apparatus according to one embodiment of the present disclosure. 
         FIG. 3  is a detailed view of the mounting arrangement of the electronic modules according to one embodiment of the present disclosure; 
         FIG. 4A  is a left side perspective view of the mounting arrangement of the electronic modules according to one embodiment of the present disclosure; 
         FIG. 4B  is a right side perspective view of the mounting arrangement of  FIG. 4A ; 
         FIG. 5  is a system schematic for the test apparatus of  FIGS. 1 to 4B  above; 
         FIG. 6A  is a detailed view of one half of the interlocking arrangement for adjacent electronic modules according to one embodiment of the present disclosure; 
         FIG. 6B  is a detailed view of the second half of the interlocking arrangement of  FIG. 6A ; 
         FIG. 7  is a perspective view of one possible arrangement of a cooling system according to one embodiment of the present disclosure; 
         FIG. 8  depicts one arrangement for the winding of a cable load according to one embodiment of the present disclosure; and 
         FIG. 9  is a schematic block diagram of one possible arrangement of a cable load according to one embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In reference to  FIG. 1  there is illustrated one possible arrangement  100  of the portable test unit  102  according to the present disclosure. As shown the unit  102  is mounted a support rack  103  which is in turn mounted within a suitable case  101  via brackets  104  such that the control panel  105  is readily accessible to the user when the case  101  is open. 
     As shown in  FIG. 1  control panel  105  includes an upper and lower portion. The lower portion in this example carries cooling fans  125 A and  125 B and the mains power socket and switch  112  which is coupled to the unit&#39;s main DC power supply  127 . The upper portion of the control panel carries the measurement display  108  which includes a LED level display  108   a  which is associated with a set of calibrated scales  108   b . Each scale is associated with a mode indicator lamp  109   a ,  109   b ,  109   c  which indicates the particular parameter being measured of the device or system coupled to the output port  111   a . Thus in order to read off the value of the given test parameter as measured the user simply reads of the value indicated by the LED level display  108   a  off the appropriate scale  108   b  as indicated by the currently illuminated mode lamp  109   a ,  109   b    109   c . In order to change the current test mode is set the user needs only to rotate the mode selection switch  115  until the desired mode lamp  109   a ,  109   b    109   c  is illuminated. While the present example provides for the measurement of three system parameters e.g. power, return loss and PIM products, it will be appreciated by those skilled in the art that any number of parameters of interest may be added. 
     The control panel  105  also includes an alarm indicator panel  106  which in this case provides an indication on the operating status of the various RF units housed below in the present case the alarm panel includes warning lights  106  associated with the units&#39; various electronic modules which in this case include a High Power Amplifier (HPA) module  119 , Low Noise Amplifier (LNA) and Frequency Synthesiser both in module  121 . A set of warning lamps  107  for the various voltage supply rails within the unit is also provided. 
     A cable load port  110  is also provided to allow for the testing of the relevant system or device under load conditions. At present the unit is provided with a 50            internal cable load  123  having a return loss rating of 17 dB and PIM of &lt;−120 dBm (for 2×43 dBm carriers). In addition to the measurement display  108  the unit  102  also provides for the use of audible tone within the return loss and PIM test modes. In order to activate the audible tone the user simply toggles switch  130  to the on position as indicated on the control panel. Once the audio tone has been activated the user can then determine changes in the measured level by the repetition rate of the audio tone. Toggle switch  130  also allows the user to adjust the output power by depressing of the switch  130  whilst the unit is in power test mode. The output power rating of the present unit is approximately 43 dBm per carrier and can be varied by ±1 dBm max by depressing switch  130 .
     While the unit provides the user with reliable measurements of system power, return loss and PIM products, port  116  is provided to allow auxiliary equipment such as a spectrum analyser to be connected to the unit  102  during onsite testing. In addition the user has the option of performing a more detailed analysis of the test results by downloading any test data stored in the unit  102  to a laptop, portable PC or the like via I/O port  114 . To enable the download of such data the mode selection switch  115  is set to off (i.e. no test mode set) and the portable PC or laptop is coupled to the I/O port. In order to initiate the download switch  130  is then depressed for a predetermined period e.g. 5 seconds. Such a download may be performed on site or offsite depending on the level of analysis required. 
     As can be seen from  FIG. 1 , a number of electronic modules are mounted in a sandwich like configuration, in the space provided between the control panel  105  and base plate  122 . It is this sandwich like construction that has allowed the applicant to incorporate an array of RF modules  119 ,  120 ,  121 , which has not previously been possible, into a single portable unit. 
       FIG. 2  is an exploded view of the unit  102  of  FIG. 1  and provides an illustration of the sandwiching concept of the present disclosure. As can be seen a number of electronic modules are arranged such that they can be stacked in vertical relation. In this example the electronic modules include a High Power Amplifier (HPA) module  119  which is positioned above a DC regulator module  120  which is in turn positioned above a frequency module  121 . The three modules are then brought into an interlocking arrangement via the engagement of a lip with a recess or groove in the adjacent module (i.e. similar to tongue and grove joint) to form a vertically stacked array  140 . This interlocking arrangement is shown in greater detail in  FIGS. 6A and 6B  as discussed below. The various circuit boards within the stacked modules are then coupled to the main control board  117  via a series of ribbon cables (not shown). Mounted behind the stacked modules is the filter module  118  which provides the RF signal output to the output port  111   a  via sub-connector  111   b . In the present example the filter module  118  includes a triplexer and at least one forward coupler and at least one reverse coupler. 
     The applicant has found by arranging the HPA  119 , DC regulator  120  and frequency  121  modules in this fashion the effects, on each of the modules, associated with the production of stray RF signals which can occur when high frequency components are brought into close relation are substantially reduced. In addition to this the applicant has also found that the arrangement is substantially easier to cool than most other arrangements and thus the arrangement has a good thermal properties and noise/interference tolerance. A more detailed discussion of one possible cooling arrangement which can be employed in the present disclosure is provided below. 
     To complete the construction the vertically stacked array  140  of the HPA  119 , DC regulator  120  and Frequency  121  modules is then secured to the base plate  122  adjacent the main DC power supply unit  127 . The base plate in this instance serves two purposes not only does it act as a secure mounting platform but it also acts as the cover plate for the frequency module  121 . Mounted to the underside of the base plate  122  are a series of supports  124  about which the internal cable load  123  is wound. As shown in  FIG. 2  the internal cable load  123  is simply wound around the supports  124  to form a rectangle. However the applicant has found that winding the internal cable load in this fashion can in some instances lead to localised over heating. A more preferred winding arrangement for the internal cable load is shown in  FIG. 8  which is discussed in greater detail below. 
     A more detailed view of the vertically stacked array  140  of the HPA  119 , DC-DC  120  and frequency  121  modules is shown in  FIG. 3 . Frequency module  121  in this instance includes a LNA  131 , a down converter log detector  132 , a Voltage Standing Wave Ratio (VSWR) monitor  133 , a plurality of frequency synthesisers  134   a ,  134   b  and  134   c  all of which are interfaced to the underside of the main control board via interface board  135  and cable bundles  136  and  137 . In the present example synthesiser  134   a  is tuned to synthesise a signal at 935.3 MHz, while synthesiser  134   b  is tuned to synthesise a signal at 884.7 MHz and synthesiser  134   c  is tuned to synthesise a signal at 50 MHz. Likewise the HPA  119  module is coupled to the underside of the control board  117  via cable bundles  138 ,  139  and the DC regulator module  120  via cable bundle  141 . 
       FIG. 4A  depicts the mounting arrangement between the HPA  119 , DC regulator  120 , frequency  121  modules and the triplexer and forward/reverse couplers of the filter module  118  in greater detail as viewed from the left. Here the filter module  118  abuts against a longitudinal edge of the vertically stacked array  140 , with the input port J 19  of the triplexer (the 935.3 MHz input) being coupled to the RF output port J 13  of first HPA circuit HPA 1  housed within the HPA module  119 . Similarly the secondary input port J 20  of the triplexer (the 884.7 MHz input) is coupled to the RF output port J 15  of second HPA circuit HPA 2  housed within the HPA module  119 . The output port J 21  (the 884.7 MHz output) of the triplexer is then coupled to the RF input of the Low Noise Amplifier (LNA)  131  of the frequency module  121 . Also shown is the secondary RF output J 2  of the LNA  131 , J 2  being directly coupled to the auxiliary port  116  on control panel  105 . Finally the main RF output J 3  of the LNA  132  is coupled to the 884.7 MHZ input J 5  of the down converter  133 . 
       FIG. 4B  shows the mounting arrangement of  FIG. 4A  from the right hand end, as shown the 50 MHz input J 6  of the down converter  132  housed within the frequency module  121  which is coupled to the 50 MHz synthesiser  134   c  via connector J 10 . The forward input J 7  of the VSWR monitor  133  is connected to the forward coupler of the triplexer and forward/reverse coupler assembly  118  via connector J 22 , while the first and second reverse inputs J 8  and J 9  respectively are connected to the first and second reverse couplers J 23  and J 24  respectively. The 935.3 MHz synthesiser  134   a  in this instance is coupled via connector J 12  to the input of the first HPA circuit HPA 1  via connector J 18 , likewise the 884.7 MHz synthesiser  134   b  is coupled via connector J 11  to the input of the second HPA circuit HPA 2  via connector J 17 . 
     As can be seen from both  FIGS. 4A and 4B  the HPA module  119  in this instance has an integrally formed heat-sink to which a fan  126  can be attached. The provision of the integral heat-sink further assists the cooling of the vertically stacked array  140 . 
       FIG. 5  is system schematic of the test apparatus of  FIGS. 1  through to  4 B further detailing the interconnection between the test unit&#39;s various electronic modules. As discussed in relation to  FIG. 4A  above the HPA module  119  is coupled to the filter module  118 . More specifically the output of the first HPA circuit HPA 1    146  is coupled to the first bandpass filter  153  of the triplexer  139  through isolator  168 , while the output of the second HPA circuit HPA 2    147  is coupled to the second bandpass filter  148  of the triplexer  139  through isolator  169 . The triplexer is then coupled to the unit&#39;s output port  111   a  through forward  129   a  and reverse  129   b  couplers and via sub-connector  111   b  (not shown). The couplers  129   a  and  129   b  are in turn connected to the VSWR monitor  133  of the frequency module  121 . 
     The output of the triplexer  139 , which in this case is taken from bandpass filter  155 , is coupled to the LNA  131  of the frequency module  121 . The output of the LNA is then coupled to a splitter  148 . One arm of the splitter  168  is connected to the auxiliary output port  116  via a 3 dB attenuator  145 . The remaining arm of the splitter is passed to the down converter  164 , which in this case comprises mixer  142  coupled to a lowpass filter  143 . The output from HPA 2  is also connected to the down converter  164  through coupler  167  via mixer  142 . The output of the down converter  164 , from lowpass filter  143  is then fed to receiver  144 . 
     As discussed above the frequency module  121  in this particular example includes three frequency synthesisers  134   a ,  134   b  and  134   c . Here the synthesisers are coupled to a temperature controlled crystal oscillator which provides a reference of MHZ. As previously mentioned the frequency module  121  is interfaced to the HPA module  119 . More specifically the output of the first frequency synthesiser  134   a  which in this case is tuned to a frequency of 935.3 MHz is coupled to the input of the first HPA circuit HPA 1    146 , while the frequency synthesiser  134   b  which in this case is tuned to a frequency of 884.7 MHz is coupled to the input of the second HPA circuit HPA 2    147 . The output of the third frequency synthesiser  134   c  which in the present case is tuned to 50 MHz is coupled to receiver  144 . 
     As shown the analogue output  136  carrying the PIM test data from receiver  144  and the analogue outputs  137  and  138  which carry the power and return loss test data respectively from the VSWR monitor  133  are coupled to the analogue inputs of the local processor  149  housed on control board  117 . The local process then proceeds to display the value of the measured parameter on LED display  108   a  or through audio speaker  151  depending on the test mode selected via mode switch  115  as indicated via lamps  109   a  to  109   c ,  113   a  and  113   b . The local processor  149  may also keep a log of the tests data collected, which may then be downloaded for later analysis via  110  port  114  on depression of switch  130  in the manner discussed above. 
     The local processor  149  is also responsible for the adjustment of the output power level on depression of switch  130  for a selected period of time, for example 3 to 5 seconds. In addition to this the local processor is also responsible for monitoring of the operating status of each of the systems modules and the various voltage supply rails provided by the unit&#39;s DC module  119 . The DC module  119  is coupled to the mains  112  via main power supply  127 . Any failures detected by the local processor in a given module are indicated to the operator via warning lamps  106  and  107  discussed above. 
     Before the test unit  102  is deployed a number of the internal units must be firstly calibrated. In order to calibrate the unit&#39;s output power the unit is connected to a main PC via the I/O port  114  and a power meter under GPIB control is connected to the output port  111   a . The main computer then adjusts the output power and reads the resultant measurement off the power meter via GPIB. Closed loop control then calibrates the power out and stores the calibration data in the unit&#39;s local processor  149 . Once calibrated the output power can be adjusted via switch  130  over a range of 42-43.9 dBm. 
     The calibration of the receiver requires the internal cable load  123  to be disconnected. A known signal level is then injected into the test port  111   a  via a signal generator. Control of the signal generator is again managed via GPIB, while the main computer monitors the Received Signal Strength Intensity (RSSI) via the I/O port  114 . The RSSI is calibrated in 1 dB steps over the range −105 to −60 dBm with the calibration data being store to the unit&#39;s local processor. 
     The VSWR unit  133  is calibrated by applying known return loss elements (5 in all) to the units test port  111   a  in the following steps 3 dB, 5 dB, 10 dB, 15 dB, 20 dB. Whilst under control of the main computer each calibrated load is applied and the return loss data stored in the unit&#39;s local processor  149 . 
     With reference to  FIGS. 6A and 6B  there is illustrated the interlocking arrangement for adjacent electronic modules according to one embodiment of the present disclosure. In  6 A the upper surface of a DC regulator module  120  is shown. The upper surface of the module  120  is provided with a central groove  156  which spans the length of the module  120 , while a recessed portion  157  extends around the outer periphery of the module  120 . The combination of the groove  156  and recessed portion  157  forms two rectangular portions  158 , the rectangular portions being shaped to fit the exposed sections  163  of the HPA circuits of the HPA module  119  as shown in  FIG. 6B . As shown in  FIG. 6B  the HPA module  119  includes a plurality of lip portions  159  which are disposed around the outer periphery and the exposed edge of internal wall  166  of the module  119 . When the HPA module  119  stacked on top of the DC regulator module  120  the lip portions  159  mate with the groove  156  and recessed portion  157  of the DC regulator module  120 , such that the rectangular portions  158  seal the exposed sections  163  of the HPA module  119 . 
     A similar type of interlocking arrangement is provided between the upper surface of the frequency module  121  and the exposed base of DC regulator module  120 . The frequency module  121  in this case is provided with a recessed portion extending about the outer periphery of the module  121 , so as to form a rectangular portion. The rectangular portion acts to seal the exposed base of the DC module  120  upon engagement of the lip portion provided on the outer periphery of the base of the DC module  120  with the recess of the frequency module  121 . The base of the frequency module is then sealed by securing the stacked HPA  119 , DC regulator module  120  and frequency module  121  to the base plate  122 . 
     One possible configuration of the cooling system of the present disclosure is illustrated in  FIG. 7 . As shown case fans  125   a  and  125   b  and HPA fan  126  are wired directly to the main DC power supply  127 . The fans in this instance are wired in a push configuration, i.e. the fans act to draw cool air in from outside the casing into the apparatus the HPA fan then forces this cooler air onto the heat-sink of the HPA  119 . Hot air is then vented through ventilation slots  160  in the rear and sides of the mounting rack  103 , and from the ventilation slots  161 , that may be provided in the upper most portion of the control panel  105 . It will be appreciated by those of ordinary skill in the art that the fans could be wired in a pull configuration wherein they pull hot air away from the unit the cool air then being drawn in through the ventilation slots  160  and  161 , or any combination of push/pull configurations. 
       FIG. 8  shows an alternate winding configuration for the internal cable load  123  which has been found to substantially reduce the occurrence of hot spotting. The cable is wound such that a number of cable loops  123   a ,  123   b  are crisscrossed from the opposing diagonal supports  124  with the remaining portion of the cable load  123  being wound around the parameter of the rectangle formed by the four supports. The opposing longitudinal side of the cable load  123   c  and  123   d  are then drawn toward each other by means of a cable tie  162 . 
     With reference to  FIG. 9  there is illustrated a one possible arrangement for the internal load  170  according to one embodiment of the present disclosure. In this particular instance the load  170  is a filtered load, which includes at least one filter  172  and a resistor  173 . The filter  172  may be a bandstop, a bandpass or a suitable filter network, the resistor is preferable a 50           50 watt resistor. The filtered load is coupled via output connector  171  to the output port  111   a  via sub-connector  111   b  (not shown). Preferably the filtered load is contained within an aluminum housing. Mounting the filtered load inside such a housing offers a number of advantages, it allows the load to be easily positioned and secured during assembly of test apparatus, it also offers better isolation and better cooling (i.e. the likelihood of localised over heating is further reduced).
     It is to be understood that the above embodiments have been provided only by way of exemplification of this disclosure, and that further modifications and improvements thereto, as would be apparent to persons skilled in the relevant art, are deemed to fall within the broad scope and ambit of the present disclosure described herein.