Icom ic-208h sticks on TX when PTT is pressed/released on the mic if the USB-C cable is not providing power?

I recently purchased a digirig and a Yaesu and Icom 9600 baud MiniDin6 audio cable. All is working fine except for one instance.

When I have the MiniDin6 connected to the digirig and then the usbc-to-usbc cable connected to the computer, I can use my radio as normal (not thru the computer). I listed and the press the PTT on the hand mic, release it when I’m done and all is good.

When I have the MiniDin6 connected to the digirig and then the usbc-to-usbc-cable is disconnected from the computer (using the usb-c port for something else at the moment) and I press PTT on the hand mic in the 2m range, the TX sticks on (indicated by the light on the radio), even after releasing the PTT button. When I press PTT in the 70cm range, all works fine (as expected).

It took me a while to narrow this done. I would be talking on various repeaters and sometimes all was working fine. Other times, it was only a problem on certain repeaters. I then tried it on simplex, just to rule out a repeater issue, and saw the same behavior in 2m and 70cm.

I know the answer could be “keep the digirig plugged into usb-c or unplug the MiniDin6 when you are not using it” but easier said then done.

Thoughts on this behavior?

My theory is quite technical: I think that when Digirig is not receiving power the line that is normally holding PTT open enters high impedance state which makes it more susceptible to RFI which in turn is further amplified by the last stage of the switch (power from the radio).


The purpose of R19 is to prevent that, but RFI must be substantial. For the experiment see if this happens with minimal RF power.

I lowered my TX power to 5w from 50w. It behaved the same way. Once the TX was stuck on, I could plug in the USB-C cable to the laptop and TX immediately went off.

My Diamond X50 antenna is currently about 6 feet from my Icom IC-208h transceiver. The antenna is sitting in a closet.

I’m afraid I don’t have other theories as to what may be holding PTT while device is powered down. There’s just nothing else there that can function without 5V DC power coming from USB.