To record audio from analogue sources, you need to convert the analogue audio to digital first and then packetize it in RTP packets and finally send the RTP packets to the recorder to be recorded.
This can be done by an off-the-shelf device such as the Barix Instreamer for line level audio sources and microphones. There are many similar products on the market and you are free to use any of them. However, when choosing one please make sure that it supports the G.711 format in RTP packets. Other features that may be useful are support for both microphones and line level audio with the same device and VoX controlled streaming mode.
For analogue 2-way radios, or digital radios with analogue recording output, you can use a device like the Omnitronics IPR100.