the Banana PI has a Line-OUT output and a little microphone.
If we study the circuit diagram in more detail then we also find a Line-IN input which is much better for Amateur Radio than the microphone.
This Line-IN is located at a small connector usually used for cameras. The good news is that Line-IN is located at Pin-1 which can be soldered with normal electronic soldering irons.
this picture shows the connector, Line-IN is at Pin-1, see the red arrow.
Use a thin AF coaxial cable and solder the inner wire to this pin-1. Then solder the screen of the cable to GND which is availabe at the top pin of a capacitor (see picture).
Now you can connect this cable to your SSB receiver, the AF level is a few 100mV as usual.
Sound card settings:
By default the sound card is setup for the microphone and we have to set this for Line-IN. The sound settings are done with alsamixer under Linux, this is how to do it under Lubuntu:
with the cursor keys left-right choose the setting. With up-down you can change the sliders and with the key 'M' you can switch on/off the switch-settings.
press F5 to select all settings.
ATTENTION: write down the currect settings, you will probably need them if you want to activate the microphone again.
Here are my settings, all other settings are switched off (MM) oder the sliders at 0.
the Line-IN is now activated.
Set the record level for your reciever:
If you want to change the input sensivity according your reciever, then use alsamixer and press
F4 ... record settings
two sliders change the sensivity: Line-IN Pre Amp and Capture, set both to about the same level as needed with your receiver.