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    IP-223 False Transmit Keying in 2 Wire Console Mode

    Question

    How do I deal with IP-223 "False Transmit Keying" in 2 Wire Console Mode?

     

    Answer

    IP-223s in Console mode, when used with a 2 wire configuration, are known to be suseptible to decoder falsing (the decoder thinks it is receiving a Transmit tone burst) when receiving high level receive signals.  This makes the IP-223 momentarily shift from Receive Mode to Transmit Mode.  The short burst of transmit audio not only causes noise on the channel, but often causes the transmitter to actually change channels, which results in dispatch traffic accidently being broadcast on incorrect channels.

    Two wire mode is susceptible to this because the transmit and receive audio are on the same pair of wires, and so the decoder is exposed to the receive traffic as well as transmit traffic from the console.  Voice frequencies of approximately 1950 Hz and above, with signal levels approaching 0.0 dB peaks at the input of the IP-223, can trigger this phenomenon.

    Resolution

    Changing the configuration of both ends of the circuit to 4 wire will eliminate the problem.  When 4 wire conversion is not available, a reduction of receive audio level into the radio end IP-223 should minimize, if not eliminate the problem. 

     

     

     

     

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    Last update:
    ‎04-08-2020 07:09 PM
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