Yaesu FT-8900 / TYT TH-9800 3.5mm Mic Input

Discussion in 'Microphones, Speakers & Audio Processing' started by KI7MUJ, Dec 5, 2017.

ad: L-HROutlet
ad: l-rl
ad: l-assoc
ad: Subscribe
ad: L-MFJ
  1. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    Hi, I have a TYT TH-9800 (compatible with FT-8900) radio that I'm trying to figure out how to turn the 6-pin RJ-12 jack on the head of the radio into a 3.5 mm jack (with PTT). This is for use with APRS, and a Raspberry Pi. I can't seem to figure out the pinout on it. I did find:


    Which looked helpful at first, but once I've connected everything, I can only get the radio to transmit if I connect the lines 6 and 4 to either mic transmit or mic ground on the 3.5mm cable. However, all that I get out of the radio is "dead air". I tried connecting pin 5 to the mic transmit on the 3.5 mm cable as well, with no luck in getting audio to pass through (connected my phone, playing a looped audio clip of me identifying my callsign, and "testing"). I've read that others have had difficulty getting this radio model to connect to a 3.5 mm jack as well- does anyone know of a fix? I'm assuming that I'll have to make some sort of a circuit to accomplish this, but I have no idea where to start.

    Any help would be appreciated!
  2. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    To clarify, I'm not worried about the PTT on this radio- driving that line to ground sends the PTT signal just fine. What I'm stumped with is that I've connected pin 5 to line out (left or right channel, tried both), and pin 4 to the sleeve on the 3.5 mm cable (ground). The radio will not receive any audio, despite my efforts. Per another suggestion that I read online, I also tried adding pin 3 (5v) to the 3.5 mm mic input via a 14K resistor- no joy there. All pins on this connector are pushing 5v except for pins 5 and 4 (which should be mic line in and ground). I've tried swapping these two pins as well, with no luck. Connector is a RJ-12 cable that has been stripped, and I'm using alligator clips to troubleshoot the connections. Again, any help would be really appreciated- this is driving me a little crazy!
  3. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    After playing around some more, I'm able to hear an extremely faint transmission, but it seems as if the audio line voltage is too low. Would an audio amplifier help here, or am I supposed to run PTT to something other than ground?
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    The Pin-out on the PI cable is different than most off the shelf cables.

    The ground connection is not the same.

    You may have better luck using a USB sound fob. Better audio quality and level adj.

    Good Luck.
  5. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    I have a soundcard for the Pi already- that's not an issue. At this point, I'm trying to troubleshoot why I can't send audio to the mic (I'm not even trying to use the Pi right now, I'm connecting both my laptop and my phone to the mic, and I'm getting a faint signal on both). What do you mean by, "The ground connection is not the same"? I'm sending PTT to an external ground for troubleshooting (car body), mic in goes to left channel on the 3.5, and ground from the radio goes to the sleeve on the 3.5.

    Here's a sweet ASCII diagram:


    Mic---------------------------------------------------------->LEFT AUDIO
    PTT----------------->external ground

    I've also tried sending PTT to the sleeve (as well as ground), with similar results.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    OK. I misunderstood your audio device.

    Are you cap coupling the audio ? What is the value of your cap ?
  7. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    Nope. I should have a capacitor on the mic line then, I take it?
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    Not sure. Normally the mic line feeds element voltage, The cap is in the mic.

    The 9V is for the Keypad not the mic element.

    I would try a external cap, Unless you are using a mic.

    The Yaesu FT-8900 and TYT TH-9800 are not 100% the same radio.

    Good Luck. You will get it figured out. :)
    Last edited: Dec 7, 2017
  9. KI7MUJ

    KI7MUJ Ham Member QRZ Page

    My mic line reads 0v, it and the ground wire are the two wires that are reading 0v. All other wires (PTT, SW1, SW2, etc read 5v. Does that help any?
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    When disconnected ?

Share This Page