I’m using an RPI4 with KM4ack’s Pi-Build software with a Digirig connected to a Yaesu FTM-400XDR radio. All seems to be working. No CAT control (of course). I set and select the VHF frequency for the local RMS station manually. I’m using VFO B in FM mode (no digital, etc). The FTM-400 PTT works fine. The signal appears to be sent with the Volume bar moving to about 3/4 level. No reply comes back to my call. I can also hear other digital traffic on that frequency so the assumption is the RMS is operating. What other indicators do I need to look for to: 1. ensure my transmission is going out correctly. 2. That the receive side is working properly.
The reasons the remote station doesn’t decode may be due to the bad audio levels or quality of RF link.
If you hear other traffic on the frequency through your radio and through the interface (listen checkbox) then in principle the receive audio works. You can use another radio to monitor the audio you send from your Yaesu.
Just wanted to add 2 cents. The 9600 Cat cable works if you just use it for 9600 transmission, but doesnt work for CAT control on the FTM-400XDR. Tested and verified.
It sounds like you are close to success. This is a good question. I monitor my outgoing signals on an HT. I’m using Windows, so I frequently get surprises in sound device and COM port assignments. The monitoring HT catches these.
RPi4/Linux is more certain, but a monitor settles any questions about outgoing.