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Only use PTT and not VOX to switch the PA with Modes with on/off keying !

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  • paulwijnand
    Hello all, A few weeks back I blew my 70 MHz driver-module and PA-transistor while using a VOX operated PA and using Opera (on/off keying). Probably the VOX
    Message 1 of 2 , Apr 1, 2012
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      Hello all,

      A few weeks back I blew my 70 MHz driver-module and PA-transistor while using a VOX operated PA and using Opera (on/off keying).

      Probably the VOX was not fast enough to switch both input and output coax relais.

      So the only safe way is to use PTT to switch PA's etc.


      All is well again, but parts are harder to get nowadays so it took a while, but with a bit more output now hi.



      73


      Paul, PA0OCD
    • graham787
      Yes, the com-port PTT option is provided for hard switching of the station, also the CAT link will switch tx/rx, if the radio has this option. Important
      Message 2 of 2 , Apr 1, 2012
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        Yes, the com-port PTT option is provided for hard switching of the station, also the CAT link will switch tx/rx, if the radio has this option.

        Important also is to check the ALC, as the audio is pulsed, using ALC can induce a large spike at the start of each pulse, Amtor/Pactor arq where the last mode's to require attention to TX alc function.

        EG: My (all) ft897 have this 'problem' that when the power is set low, using a peak detecting power meter you can measure nearly full power, best to reduce the audio drive to the minimum to prevent over shoot.

        73-G..

        --- In O_P_E_R_A_@yahoogroups.com, "paulwijnand" <paulwijnand@...> wrote:
        >
        > Hello all,
        >
        > A few weeks back I blew my 70 MHz driver-module and PA-transistor while using a VOX operated PA and using Opera (on/off keying).
        >
        > Probably the VOX was not fast enough to switch both input and output coax relais.
        >
        > So the only safe way is to use PTT to switch PA's etc.
        >
        >
        > All is well again, but parts are harder to get nowadays so it took a while, but with a bit more output now hi.
        >
        >
        >
        > 73
        >
        >
        > Paul, PA0OCD
        >
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