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I'm trying to wire up an external mic with PTT and a speaker to my Yaesu FT-250R to basically use as a VHF base station when I'm not mobile. Unfortunately, I can't find anywhere a description of how to wire that up. The FT-250R has a single 3.5 mm TRRS plug for connecting an external mic/speaker. Just hooking up a plug with bare wire leads and fiddling around with things, I'm pretty sure I've figured out which are AUDIO OUT, GND, and PTT. However, a lot of the diagrams for similar radios that I've seen have MIC and PTT going to the same ring on the 3.5 mm connector. They then show you having to insert a capacitor in the MIC line and a resistor (typically ~2k) in the PTT line to decouple the two. In my fiddling around, inserting a 2k resistor between GND and any of the other leads did not cause the radio to key; but shorting one of the leads (the one I assume is PTT) to GND did cause it to key.

Anyway, I kind of have it figured out, but I want to be a little more confident in what I'm doing before I go much further so I don't ruin my radio. If anyone has any advice or access the the appropriate wiring diagram, I'd really appreciate it.

Yes this probably would be easier to buy the CT-44 adapter that Yaesu makes, but I'm a homebrew kind of guy and have enough spare parts to do this a few times over.

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    $\begingroup$ Not sure if you've seen this in your travels: pinoutguide.com/PortableDevices/… But it indicates a resistor is used as part of the PTT circuit. It calls out pin-outs for models that use the CT-44 specifically at the bottom. See if this matches up with your other findings. $\endgroup$
    – user21417
    May 9, 2022 at 20:51
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    $\begingroup$ Also, an image search for "Yaesu ct-44 pinout" shows a lot of schematics you can also use to verify your findings. $\endgroup$
    – user21417
    May 9, 2022 at 20:57
  • $\begingroup$ That first one looks like exactly what I need. Thanks! I'll see what I can figure out from that. $\endgroup$
    – byl
    May 10, 2022 at 23:04
  • $\begingroup$ Make sure you come back and self-answer so we have a canonical answer! $\endgroup$
    – user21417
    May 11, 2022 at 0:18

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Using the link John suggested in the comments and some fiddling around, I figured out the proper pinout. It's:

Tip: AUDIO OUT

Ring 1: CLONE

Ring 2: MIC/PTT

Sleeve: GND (you can verify there is a short between this and the ground for the antenna connector)

As described in the operator's manual for the FT-250R (see picture below), you need to decouple the MIC and PTT with a capacitor and a resistor. The values shown below worked great for me, though I think I'm going to up the capacitor to 47 uF, since the mic gain is a little lower than I'd like.

enter image description here

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  • $\begingroup$ Nice self-answer, and a good reference for future spelunkers. $\endgroup$
    – user21417
    May 11, 2022 at 16:12
  • $\begingroup$ Thanks for this. Can someone confirm what "CLONE" indicates? I'm assuming it doesn't need to be wired, given the graphic. Is this correct?: i.imgur.com/AOT0iI6.png $\endgroup$
    – Michael
    Nov 12 at 9:59
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    $\begingroup$ Since I just wanted to hook up a mic and a speaker, I left "CLONE" unwired. Not sure what it does... $\endgroup$
    – byl
    Nov 13 at 16:15

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