Distorted TX audio with YAESU FT710

[nvelickovic10]

Title: Distorted audio tone when using FT-710 with FT8AF (clean tone on phone speaker)

Description:
When I use the FT8AF application and monitor the transmission directly from the phone speaker, I get a clean single-tone sound (pure sine wave).
However, when I connect my Yaesu FT-710 to the phone, the transmitted audio is no longer clean. The tone sounds distorted and is not a pure sine wave.

Device details:
Phone: Xiaomi Redmi Note 12 Pro+ 5G
OS: HyperOS 2.0.10.0
Radio: Yaesu FT-710
USB link: phone -> HAMA OTG adapter -> Tripp litte USB cable -> FT710

The issue appears only when the radio is connected. Without the radio (monitoring directly from the phone), the tone is clean.
Please advise what could be causing this distortion.

I have been playing with USB MOD GAIN and other sound settings but to no avail...

Thank you for your work!

[Reid-n0rc]

@nvelickovic10 What is your ALC meter showing?

[Reid-n0rc]

@nvelickovic10
Also, are you able to see what the signal is over the air?

I have a FT-710 and the TX waterfall can get wonky sometimes. My HF antenna for the FT-710 and shack is torn apart, otherwise I'd check it right now.

[nvelickovic10]

@Reid-n0rc
ALC meter showing normal levels, which in my case is barely any movement from 0. I only like to see just a small jump on the needle.

Now to save everyone some time and trouble I tried the app on a Samsung A07 phone and it is working flawless. My ruling is that Xiaomi is doing some obscure audio processing and I was not able to locate any options in the settings to mitigate the issue.

For now I will be using the Samsung as my field operator.

Thank you all you can close the ticket as far as I'm concerned. If on the other hand you are interested in entering the rabbit hole I will be assisting you in any way necessary.

[Reid-n0rc]

Let's not close it just yet. This is an interesting edge case that might impact more people than we realize.

I can't work on it at the moment but will try to look more later.

[nvelickovic10]

Cool, I'm waiting for instructions. 73

[patrickrb]

Thanks @Reid-n0rc ! I'll see if I can find anything today

[patrickrb]

Thanks for the detailed report — the "clean on the phone speaker, distorted only when the FT-710 is connected" symptom is a really useful clue, and I've traced the TX audio path to narrow this down.

The app has two different ways it can send TX audio to a USB radio, and which one you're on completely changes what's going on:

1. Android USB-audio path (AudioTrack) — used when you pick the FT-710 as a normal audio output device. Here the app hands the exact same audio to Android for both the phone speaker and the radio; the OS/USB driver does the 12 kHz → 48 kHz conversion. If distortion appears only over USB on this path, it's happening in the phone's USB-audio driver or in the radio's input stage — not in app code.
2. USB-direct (libusb) path — used only when you explicitly select the "(USB direct)" entry in Audio settings. This path does its own resampling in the app, and there's a known weakness there (a simple linear-interpolation upsampler) that can add harmonics.

To fix the right thing, could you help with two quick items?

1. Which output are you using? In the app's Audio settings, is the FT-710 selected as a normal output device, or did you pick the entry that says "(USB direct)"?

2. Can you send the debug log? It records exactly which path fires. Pull it with:

adb pull /sdcard/Android/data/radio.ks3ckc.ft8af/files/debug.log

(or grab it via a file manager on the phone) and attach it here. The lines around a transmit that start with playFT8Signal: will say either using USB audio (direct) output or using AudioTrack output, plus the sample rate/channels.

In the meantime, a couple of things worth ruling out, since "distorted only through the radio" very often comes down to input level into the radio's modulator rather than the tone itself:

• In the FT-710 menu, make sure the data/USB input mode and level are set for digital modes (Yaesu's RADIO SETTING → MODE PSK/DATA and the DATA gain), and watch that ALC stays low on transmit. Full-scale USB audio into the radio can overdrive the modulator and produce exactly this "not a pure sine" distortion even when the source tone is clean.
• Try lowering the app's TX output level as well as the radio-side USB/DATA gain together, rather than only one.

Once I know which path you're on (and ideally see the log), I can tell whether this is fixable in the app (e.g. improving the USB-direct upsampler) or whether it's a level/setup issue on the radio side. Thanks!

[Reid-n0rc]

Thanks for the detailed report — the "clean on the phone speaker, distorted only when the FT-710 is connected" symptom is a really useful clue, and I've traced the TX audio path to narrow this down.

That's not really the issue @patrickrb. If he changes phones it cleans up.

[patrickrb]

Gotcha, lets just make sure the settings are the same on both devices. I added some debug info to the logs that should help narrow this down

[nvelickovic10]

Hey guys, thank you for your replies.

I'll try providing asked info today or tomorrow, please excuse me but my workdays are brutal :D

[nvelickovic10]

OK, here is the deal:

Playing with the USB gain and TX volume doesn't fix the issue at all. The harmonics are still there, just lowered in volume.

As for the USB path, I've tried all of the settings and they both have the issue. If you check the provided log you can see I've used different audio sinks. Both have the same issue, but one of the USB audio sinks is considerably louder than the other.

Check the log file, I'm sure you will make more sense of it than me. Good luck :D

debug.log