What is the difference between "T" (TDMA) and "D" (Digital) as shown in the database. I have a GRE PSR 800 and live in Tennessee. The scanner picks up THP just fine, which is shown in the database as "D". However, it has not been receiving the TDOT HELP trucks, which are shown in the database as "T" which stands for TDMA. According to all I've read, this scanner is TDMA Phase 1 and Phase 2 capable. When the scanner tries to receive the TDOT HELP trucks, it flashes and only displays a "VC" and no voice. Thus, my question, what's the difference?