Audio Troubles: DigiRig Mobile + ICOM IC-9100 + Direwolf AX.25 (9600 baud G3RUH)

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Hello everyone, I’m looking for some help getting Linux audio working for 9600 baud AX.25 with an ICOM IC-9100. I’ve been dealing with this issue on and off for a long time now; my apologies if this is the wrong forum for this issue.

I know this is a little odd, but I’m only concerned about transmitting AX.25, not receiving. Direwolf doesn’t seem to handle the demodulation scheme I need.

I’ll start with the setup:

  • Linux Computer.
    • Ubuntu, older version
    • PulseAudio
    • Direwolf
  • DigiRig Mobile
    • I use USB-A to connect to a USB-A port on the front side of the computer, then plug into the USB-C on the DigiRig mobile.
  • ICOM IC-9100
    • I connect from the audio output on the DigiRig Mobile to the DATA2 input on the back side of the ICOM IC-9100 using this cable, bought from the DigiRig online store.
    • 9600bps Mode is set to ON.
    • DATA MOD is set to ACC
    • The main channel (which it does transmit on) is set to a 2m frequency on FM-D.
    • The filter is set to 1 (15 kHz)

I’ve found that I can only set the DigiRig output volume on my computer as high as 53% (-16.52 dB). If I go a little higher, the radio has a weird double transmit and the signal is distorted. If I turn the volume up much higher (say, 100%), the radio refuses to transmit at all.

Unfortunately, the FM deviation the radio outputs at only 53% volume is less than 0.25 kHz (see screenshots), much less than the 3.5 kHz that the receiving radio expects per its datasheet.

I’m at a loss on how I can increase the FM deviation, any ideas would be greatly appreciated.

If it helps, here are a few screenshots from an SDR I’m running near the ICOM IC-9100. The SDR decodes the packet just fine, but the target radio struggles to decode the signal consistently.

895×1008 202 KB

^ Single transmission at the 53% volume. (Taken during transmission)

GNU Radio screenshot of transmissions on a waterfall.
GNU Radio screenshot of transmissions on a waterfall.895×1008 203 KB

^ Multiple transmissions at 53% volume. (Not taken during transmission. The multiple transmissions are only visible on the top graph, the bottom two are near instantaneous readouts and are showing background noise).

Please let me know if you have any questions. I have access to test equipment and can try to provide oscilloscope measurements of the DigiRig, if needed.

Thank you,

Liam KI5JXQ

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Here is more information, in case it proves helpful.

I just tried using Windows instead of Linux and I have gotten approximately the same result. I was not able to produce more deviation on Windows than on Linux, and turning up the volume any more resulted in the double transmit. Even more volume resulted in no transmission.

I’ve also tested with another DigiRig and received the same results. I’m going to assume it’s not a computer or DigiRig issue. I also tried using a different IC-9100, and the same results occurred. Perhaps the radio model isn’t really capable of 9600 digital, or at least not at any meaningful FM deviation?

I suppose what I have is workable, but not ideal. I’m still open to ideas if anyone has them.

Thanks,

Liam KI5JXQ

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does the ic-9100 have a data mode input gain menu setting (for the acc port) ?

you’ve got the data mode set to acc but is there a separate gain control ?
(there is on the 7200, closest thing i’ve worked with to a 9100)

mic,usb,acc all had discrete gain controls.

good luck
:slight_smile:
kb0wlf