FAQ X108G PTT switching using the ACC port

Discussion in 'X-108' started by DD5LP, Dec 3, 2020.

  1. DD5LP
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    DD5LP Crack-Boarder X-108 Member

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    Hi All,
    I wonder if anyone here is using the accessory port on the X108G (Outdoor/OLED version) to connect a microphone instead of the front socket? Why would you do that? Well, the normal Mic socket expects a relatively high output condenser type microphone (the same as most of the ICOM rigs). If one wants to use a different microphone type, not only do you need to add a 1 uFd decoupling capacitor to protect the microphone element from the 8v bias (aka phantom power) voltage on the mic line, you also need to adjust the audio input level using the small pot inside the rig. Well if changing permanently to the lower output (e.g. Dynamic) microphone you could do this but I'd like to be able to switch between the standard microphone and my new one. Another way to get audio into the X108G (normally used for data modes) is the ACC 6 pin mini-DIN socket on the rear of the rig, this line bypasses the volume control and goes directly to the first audio amplifier stage and hence supplies the full available microphone output to the rig.
    upload_2020-12-3_16-47-11.png

    Of course, to operate with a microphone, you need a way to turn the rig on and off transmit i.e. "PTT". There is a PTT line in the ACC socket, however, it is very clearly marked "output" but in fact looking at the circuit diagram:

    upload_2020-12-3_16-38-17.png

    It looks to me as if this connection has been designed to work both ways - see the two optoisolators U3 & U16. Earthing one leg of U16 through the 100 Ohm resistor R127 will cause U16 to switch and put a PTT request on the "PTT_Ext" line back to the microcontroller. While if you are using the Mini-Din for a connection to turn on and external amplifier (for example) - then signal received on the PTT line to U3 will cause it to switch and you get an earthed via 100 ohms connection back out of the rig.

    Considering the thought that has gone into this circuit, it seems strange to me that Xiegu specifically say PTT output in their manual for pin 2 of the ACC socket!

    73 Ed.
     
  2. DD5LP
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    DD5LP Crack-Boarder X-108 Member

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    Just a quick update that I have tried using the PTT connection in both directions on the X108G and earthing it from an external device puts the rig onto transmit. I have also used this with an external reed relay to switch a small 100-watt amplifier. So the pin is indeed "2-way".
     

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