I noticed some Motorola PR400s floating around and the presence of the talk-permit-tone chirp when a user keys up. From my understanding, this is only possible via a LTR system for this radio (without the "DTMF hack" etc.) Does anyone have any info on a possible LTR system or why the PR400 would have the TPT active? I have not found any records of such a system at Penn State. Perhaps I am just overlooking something as well. Thanks in advance for any help!