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    Life test of RF connectors
     

    For a RF test cable assembly, the application engineer is concerned not only with the specifications when it leaves the factory, but also with its service life.
    The life of RF cable assemblies depends on three factors: the bending resistance of the cable itself, the good connection between the cable and the junction and its bending resistance, and the life of the junction. The first two factors can be guaranteed by fixture or by standardizing the operator''s action, while the life of the joint can only be guaranteed by the quality of the joint itself and the assembly process.
    Taking the N-type connector as an example, the plug-and-pull life of the N-type (copper) connector is 500 times stipulated in the international standards of the radio frequency connector, such as MIL-C-39012 and IEC 60169-16.
    MIL-C-39012 is described as follows: at least 500 inserts and pulls per minute in 12 laps per minute, the connector should meet the matching requirements. In IEC 60169-16, the minimum insertion life is 500 times under the torque condition of 0.7-1.1Nm.
    In our conversations with the users of the RF test cables, we often hear voices like this: 500 times? Too few, we need at least a few thousand times!
    The reason for this understanding is that there is no understanding of the specifications specified in the various application conditions and standards for connectors. By carefully analyzing the additional conditions of the specifications specified in the standard and combining with practical experience, the following conclusions can be drawn on the life definition of RF connectors:
    1) the life of the 500 time is the index under the condition of N type connector specified torque (0.7-1.1Nm). To achieve this torque, a special torque wrench is needed, which can not be achieved by normal operation of ordinary people. The author has done an experiment on the N-type connector: when the hand is felt to have been tightened, the standard torque wrench (H&S P/N 74 Z-0-0-193) can be used to tighten nearly half a circle.
    2) The meaning of the so-called 500 life is: when in accordance with the provisions of the torque insertion within 500 times, all electrical indicators are guaranteed to be within the specified range of factory indicators. Taking the test cable produced by Izeko as an example (Nm-Nm, 1 m long, RG223-03-03-1000A), its factory output index is insertion loss 0.84-1.3 dB/dc-3GHz standing wave ratio is 1.15-1.25@dc-3GHz. After inserting 500 times, the above indicators can still be guaranteed.
    3) Except for precise measurement and calibration tests, expensive standard torque wrenches are rarely used to disassemble and assemble RF connectors on the production line, so that in actual use, the RF connector bears far less torque than the specified value.  At the same time, the connector which is tightened by manpower can completely meet the requirements of the index. This creates conditions for prolonging the service life of connectors.
    4) As a supplier of test cable assemblies, Izeko does not want to extend the life of RF connectors only by reducing torque, but by ensuring a long enough life from the quality of the connectors themselves.
    Then, how long is the life of a RF connector? In order to obtain a relatively accurate data, the author conducted a plug-in life test of radio frequency connectors.
    The test object of plug-in and pull-out life test method for RF connector is a RG223 test cable assembly (EZCON P/N:RG223-03-03-1000A) with a length of 1 meter and two ends of N M. The screw sleeve and outer conductor of the tested N m connector are made of copper-plated ternary alloy material, and the inner conductor is made of gold-plated brass. The experiment was carried out under the following conditions:
    1) For one end of the Nm interface, a Nf connector is connected and disassembled by a wrench. In order to ensure accuracy, Nf joints made of stainless steel are used. In general, the life of the connectors made of stainless steel is 1000 times, which is twice as long as that made of copper.
    2) The insertion loss of the cable assembly and the standing wave of the interface of the tested end are measured once every 100 inserts and pulls, and the values at 2.2 GHz frequency point are recorded. The experiment was conducted 2400 times.


    Life test results
    The final test results are shown in Figs. 2 and 3, where Fig. 2 (a) shows the change of insertion loss with insertion times at 2.2 GHz and Fig. 2 (b) shows the change of standing wave with insertion times at 2.2 GHz.


    The red trend line in Fig. 2 of the RF connector life test (point frequency) shows that, although the measured values fluctuate somewhat, the insertion loss of the cable assemblies always increases with the wear of the connectors, while the standing wave has no obvious deterioration, and the typical value remains between 1.07 and 1.09. Fig. 3 (a). Insertion loss versus insertion times (sweep frequency) Fig. 3 (b). Standing wave versus insertion times (sweep frequency) Fig. 3. Life test (sweep frequency) of radio frequency connectors Fig. 3. Insertion loss and standing wave variation under sweep frequency conditions. Indicators from 10MHz to 3GHz were recorded for 1000, 1600 and 2000 insertions, respectively. The sweep results show that the insertion loss and the variation of standing wave are consistent with the point frequency.
    Conclusion:
    1) under normal use, the life of the RF connector will exceed the standard value of 500 times.
    2) in the whole frequency band, there is no phenomenon of insertion loss and standing wave jumping.
    3) The insertion loss of the RF connector increases gradually with the mechanical wear, while the standing wave hardly changes there seems to be no obvious failure point in the process, so in the production line, if no obvious fault of the cable is found, the compulsory scrapping system should be established to ensure the test index. In this paper, the plug-and-pull life of RF connectors is studied from the application point of view, so only two indicators concerned by RF test engineers are evaluated. Other indicators of RF connectors, such as

    date2018-8-23 Read1205second
     
     
     
     
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