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Just about every DMR radio out there is a Tier-2, or Tier-3 if trunking is used. DMR is usually thought of as just TDMA. There is DMR Tier-1 which operates in FDMA mode, referred to as a continuous transmission mode. The only ones I know that do are the license free digital PMR446 radios in the EU. Anyone else know of a DMR Tier-1 radio? I'm curious about how a Tier-1 and Tier-2 radio would interoperate. Also is there really any difference between a Tier-1 radio and a Tier-2 radio when operating in simplex mode? I've read several different opinions about it. Some say it's single slot while other claim it's double slot. Then there is the issue of DCDM, Dual Capacity Direct Mode. And, apparently there are two flavors of that too. I've been digging through the technical documentation and it's sketchy what Tier-1 really does, and if its compatible with Tier-2. I found the attached in one of the ETSI DMR standards documents. In the documentation "BS" refers to a Base Station and "MS" refers to a Mobile Station.