Multiple Realms

Hi, I have spent some time reading and trying to configure multiple realms to no avail. Basically I currently have one active realm and need to have another realm configured onto the same radius box. For example dsl.example.com.au is one and voice.example.com.au is the second. How can I configure the second? I know it's somewhat to do with proxy.conf file, but not sure how or where to do this. Thanks