Salut Guillaume: There are many experts on this list who may respond to you. I am not one of these but will explain my understanding while you wait for more complete information. There are two important configuration files: The rpt.conf file determines the operational modes (simplex, duplex, etc), DTMF codes, CW ID, remote base programming et al. This file is used for all the various radio interfaces. The usbradio.conf file sets up the USB FOB parameters and is unique to that interface. Switching between receive and transmit can be done in two ways: DSP squelch generation or hardware COS (carrier sensing). This selection is made in the usbradio.conf file. Audio and DSP sensing levels are adjusted with the 'radio tune' utility, as described in http://app-rpt.qrvc.com/usbradio.pdf The files iax.conf and extensions.conf also need additions to support app-rpt operation. The best documentation that I have found are the sample conf files (and the C source code) which show every option. The question is: Which options does one need? I am sure that many members of this list would provide you with copies of their customized conf files for you to study. If you wish mine, please contact me off-list. An important consideration is the point from which you extract the audio from your receiver. If you wish to use DSP squelch generation and CTCSS detection, the audio should be taken prior to the de-emphasis network, i.e. the discriminator. Je vous souhaite la bonne chance! David VE7MQ.