Abstract:
A system and method for enhanced use of voltage standing wave ratio (VSWR) tests of an avionic radio and antenna is disclosed. A signal processor/generator conducts a VSWR test of an antenna and archives the result within a database. Multiple tests are conducted spanning periods of operation of the radio. Tests may also be conducted at multiple frequencies, such as commonly used channels of communication. Results are uploaded to an external diagnostic device and analyzed to evaluate deterioration of the antenna. Analysis may including comparing test results to threshold values and analyzing test results for frequency and time dependent trends.

Description:
BACKGROUND OF THE INVENTION 
   Modern aircraft rely heavily on radio contact with ground based communication systems. In addition to conventional air traffic control communications, aircraft may use radio communication to upload weather information and provide telephone and data communication for passengers. In many aircraft one or more antennae are positioned below the aircraft to facilitate communication with ground based transmitters. In many instances such antennae are exposed to airborne water and contaminants as well as water and dust raised by the landing gear. Accordingly, antennae, cables, and couplers connecting the externally positioned antenna to internal cables are subject to deterioration due to corrosion and contamination. 
   Inefficient or defective performance of antennae, cables, and connectors is difficult to detect. In prior systems, a voltage standing wave ratio (VSWR) test function provided by the avionic radio enables evaluation of impedance differences between the internal circuits of the communications system and the antenna and cables. A result substantially above unity from the VSWR test function may result from a defect within the avionic radio or defective performance of the antenna, cables, or connectors. A non-unity results may prompt an operator to remove the radio for repair by a technician only to find that the radio is perfectly operable, while the antenna, cables, or connectors are defective. This process results in unnecessary interruption of aircraft service and wasted labor on the part of the repair technician. 
   In view of the foregoing it would be an advancement in the art to provide convenient systems methods for evaluating operability of a radio antenna and associated cabling without removing the communication system from the aircraft. 
   BRIEF SUMMARY OF THE INVENTION 
   A method for evaluating transmission equipment includes a communication system configured to repeatedly conduct a voltage standing wave ratio (VSWR) test on a an antenna electrically coupled to an electrical signal processor/generator, such as a radio, to generate a plurality of VSWR test results. The VSWR test results are stored in nonvolatile memory within the signal processor/generator. The VSWR test results are uploaded to an external memory bearing device selectively connected to the signal processor/generator. The external device analyzes the data to evaluate the condition of the antenna. Analysis may include analyzing trends in the data, such as time dependent trends. 
   In some embodiments VSWR tests are conducted in series across a range of frequencies. The stored results of such tests may be analyzed for frequency dependent trends. The frequencies tested may correspond to commonly used communication channels. In one context the frequencies are 118, 120.1, 122.2, 124.3, 126.4, 128.5, 130.6, 132.7, 134.8, and 136.9 MHz. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
       FIG. 1A  is a perspective view of an aircraft communication system formed in accordance with an embodiment of the present invention; 
       FIG. 1B  is a schematic representation of an antenna, cable, and coupler used in the aircraft of  FIG. 1A ; 
       FIG. 2  is a schematic block diagram of an avionic radio having enhanced VSWR testing functionality formed in accordance with an embodiment of the present invention; and 
       FIG. 3  is a process flow diagram of a method for enhanced VSWR testing formed in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1A and 1B , an aircraft  10  typically has one or more antenna  12 . To facilitate communication with ground based transmitters. The antennae  12  may be positioned on the lower side of the aircraft  10 . A cable  16  or series of cables or other conductor, connects the antenna  12  to an avionic radio  14 . A coupler  18  connects the internal cable  16  to the external antenna  12 . 
   Referring to  FIG. 2 , in one embodiment the avionic radio  14  includes a communication module  24 , a testing module  26 , an archiving module  28 , and an analysis module  30 . A communication module  24  facilitates communication between the avionic radio  14  and an external diagnostic tool  38  in order to offload display test results on the tool to an operator. In one embodiment, the communication module  24  communicates with a PCMCIA card, or similar device, connected to a desktop, notebook, or other computer serving as the diagnostic tool  38 . The desktop, notebook, or other computer, may execute diagnostic software. In other embodiments, a handheld diagnostic tool  38  couples to the avionic radio  14 . In still other embodiments, the test results are written to removable memory coupled to the radio  14  and then transferred from the external memory to the diagnostic tool  38 . 
   A testing module  26  conducts a test of the VSWR of the antenna  12 , cable  16 , and any couplers  18 . Differences in the impedance of the antenna  12  and the impedance of the cable  16  and couplers  18  will result in a VSWR result above unity. A non-unity VSWR result may also result from poor connections at the couplers  18  or corroded or worn portions of the cable  16 . The testing module  26  tests VSWR at regular time intervals, upon powering on of the avionic radio  14 , upon receiving an input from an operator, or some other manual triggering event. 
   In some embodiments, the testing module  26  tests the VSWR at various frequencies. Impedance is frequency dependent. Accordingly, impedance mismatches may be present at some frequencies and not others. Accordingly, the deterioration of the antenna  12 , cables  16 , and coupler  18  is monitored more closely by testing multiple frequencies in order to provide advanced notice of catastrophic failure. 
   In one embodiment, the testing module  26  sweeps the entire frequency range of the avionic radio  14  while sampling the VSWR at fixed time or frequency intervals. Alternatively, the testing module  26  evaluates VSWR at discrete frequencies at regular intervals. Intervals are regular on a linear or logarithmic scale or are varied to accommodate frequency response characteristics of a radio  14 . Tested frequencies may correspond to frequency channels frequency used for avionic communications. In the illustrated embodiment, frequencies of 118, 120.1, 122.2, 124.3, 126.4, 128.5, 130.6, 132.7, 134.8, and 136.9 MHz are tested. 
   In one embodiment, results of the VSWR test are converted to an N bit word, such as an eight bit word. Alternatively, the VSWR results are compared to a threshold value and a single bit word indicating whether the VSWR is greater than or less than the threshold is stored as the test result. 
   The archiving module  28  stores the results of the VSWR tests within a database  32 . In one embodiment, the results may be stored within records  34  corresponding to the frequency tested. Individual entries  36  within a record  34  correspond to VSWR tests conducted at different times. The entries  36  store both a VSWR value and a time of testing in order to allow first, second, and higher order derivative based trend analysis on the test results. Alternatively, where the testing module  26  is configured to test at regular periods, the time interval between tests is assumed and need not be recorded in order to analyze time dependent trends. 
   The entries  36  accumulate within a record  34  until the record  34  is full. Alternatively, the record  34  functions as a rotating stack with newest test result overwriting oldest test results and a pointer being maintained to indicate the locating of the newest or oldest entry  36 . 
   Various means for storing the test results are possible. For example, the records  34  may correspond to a series of tests conducted at about the same time whereas the entries  36  correspond to test results at different frequencies. In still other embodiments, test results are stored as an undifferentiated block of data interpretable by assuming that every N test results correspond to N frequencies tested for each series of tests conducted. 
   In some embodiments, an analysis module  30  analyzes the archived data within the database  32 . Analysis may include time and frequency dependent analysis of the test results. In some embodiments, the analysis module  30  is omitted and the functionality of the analysis module  30  is provided by the external diagnostic tool  38 . In one embodiment, the analysis module  30  outputs a result on a display  40  coupled to the radio  14 . An output may be a number or series of numbers summarizing the analysis or a pass/fail indicator. The display  40  may be one or more dial indicators, LEDs, LCDs, or the like. 
   Analysis may include evaluating whether any one test result, or a local average of test results, falls above a predetermined threshold value. Alternatively, a sum or average of tests across multiple frequencies is compared to a threshold value. Values exceeding the threshold value trigger an indication of failure to the operator. In one embodiment, the threshold value is well below the value for VSWR indicating catastrophic failure of the antenna  14 , cable  16 , and/or coupler  18 . The threshold value may also represent the point at which power transmission through the antenna  14  is inadequate in view of the distance between the aircraft  10  and a receiving facility. Multiple threshold values may be used to indicate various degrees of deterioration of the antenna  12  and connecting structures. For example, exceeding one threshold value indicates that replacement should occur soon whereas exceeding another indicates that the antenna is unsafe to use. Indications displayed to the operator may indicate the highest of the multiple threshold values that has been exceeded. 
   In one embodiment, advanced notice of failure is provided by evaluating first, second, or higher order derivatives to determine increases in the rate of deterioration. Derivatives are calculated for each frequency tested or based on averages calculated across frequencies. Values of first, second, or higher order derivatives are compared to threshold values or to prior calculated values for the derivatives to detect changes in the rate of deterioration that may indicate physical damage to the antenna  14 , cables  16 , and coupler  18 . 
   In some embodiments, test results are mathematically distilled into one or more values characterizing the results. For example, a mean and standard deviation are calculated across all frequencies, or groups of contiguous frequencies, for a series of tests performed at about the same time. A maximum, minimum, average, twenty-fifth percentile and seventy-fifth percentile may likewise be evaluated. Such values may be reported to an operator or compared to thresholds indicating proper operation in order to anticipate failure of the antenna  14 , cables  16 , and coupler  18 . 
   Referring to  FIG. 3 , an example method  42  performed by the radio  14  for enhanced VSWR testing begins at block  44  by setting a carrier frequency. VSWR is evaluated at block  46  at the frequency set at block  44 . The results of the VSWR test are archived at block  48 . The functions of blocks  44 ,  46 , and  48  may be repeated, setting a different frequency for each iteration, or repeated at different times, such as periodically or upon powering on of the radio  14 . The functions of blocks  44 ,  46 , and  48  may also be repeated both at different frequencies and at different times. 
   The method  42  further includes uploading the test results to a diagnostic tool  38  at block  50 . At block  52 , the test results are analyzed to identify frequency dependent trends according to the mathematic methods described above. At block  54 , the test results are analyzed to identify time dependent trends. Test results are compared to threshold values to evaluate antenna performance at block  56 . 
   At block  58 , the results of the analysis are outputted to an operator. Output may be by means of a screen, lights, printouts, audible alarms, and the like. In some embodiments, blocks  52 ,  54 , and  56  are omitted, in which case the step at block  58  includes providing the data, or a graphical or tabular summary of the data to be analyzed by another device or by an operator. 
   In the illustrated embodiment, steps within box  60  are typically conducted on the radio  14 . Steps within box  62  are conducted on the external diagnostic tool  38 . In some embodiments, one or more of the analyzing steps (blocks  52 ,  54 , and  56 ) and output step (block  58 ) are also performed within the radio  14 . In such embodiments, the uploading step  50  would be omitted. In still other embodiments, the step of archiving data (block  48 ) is performed by the external diagnostic tool  38  coupled to the radio  14  that receives the results of the testing step (block  46 ). 
   The various steps and ordering of steps of method  42  are exemplary only. Steps may be omitted or reordered without departing from the scope of the invention. 
   While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.