DMR Repeater ~ ARC W4HFH Alexandria, Virginia
Input Output Offset Color Code
447.4125 442.4125 -12MHz 1
Network – Virginia DMR (VADMR)
|TAC A / Chat 1||1||27501||PTT|
|TAC B / Chat 2||1||27502||PTT|
|Clear Time Slot||2||27000||PTT|
The Alexandria Amateur Radio Club’s use of DMR radio equipment was deployed in the interest of club members and the radio community-at-large.
“What’s Digital Mobile Radio (DMR)?” is a limited open digital mobile radio standard defined in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1–4 and used in commercial products around the world. DMR, along with P25 phase II and NXDN are the main competitor technologies in achieving 6.25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder. DMR use two-slot TDMA in a 12.5 kHz channel, while NXDN uses discrete 6.25 kHz channels using frequency division and TETRA uses a four-slot TDMA in a 25 kHz channel.
DMR was designed with three tiers. DMR tiers I and II (conventional) were first published in 2005, and DMR III (Trunked version) was published in 2012, with manufacturers producing products within a few years of each publication.
The primary goal of the standard is to specify a digital system with low complexity, low cost and interoperability across brands, so radio communications purchasers are not locked into a proprietary solution. In practice, given the current limited scope of the DMR standard, many vendors have introduced proprietary features that make their product offerings non-interoperable with other brands.
DMR Tier I
DMR Tier I products are for licence-free use in the European PMR446 band. Tier I products are specified for non-infrastructure use only (meaning without the use of repeaters). This part of the standard provides for consumer applications and low-power commercial applications, using a maximum of 0.5 watt RF power.
Note that a licence free allocation is not present at this frequency outside of Europe, which means that PMR446 radios including DMR Tier I radios can only be used legally in other countries once an appropriate radio licence is obtained by the operator.
Some DMR radios sold by Chinese manufacturers (most notably Baofeng) have been mis-labelled as DMR Tier I. A DMR Tier I radio would only use the PMR446 licence free frequencies, and would have a maximum transmitted power of 0.5 W as required by law for all PMR446 radios.
Although the DMR standard allows Tier I DMR radios to use continuous transmission mode, all known Tier I radios currently use TDMA, the same as Tier II. This is probably due to the battery savings that come with transmitting only half the time instead of continuously.
DMR Tier II
DMR Tier II covers licensed conventional radio systems, mobiles and hand portables operating in PMR frequency bands from 66–960 MHz. The ETSI DMR Tier II standard is targeted at those users who need spectral efficiency, advanced voice features and integrated IP data services in licensed bands for high-power communications. A number of manufacturers have DMR Tier II compliant products on the market. ETSI DMR specifies two slot TDMA in 12.5 kHz channels for Tier II and III.
DMR Tier III
A portable radio compatible with the DMR Tier III digital radio standard.
DMR Tier III covers trunking operation in frequency bands 66–960 MHz. Tier III supports voice and short messaging handling similar to TETRA with built-in 128 character status messaging and short messaging with up to 288 bits of data in a variety of formats. It also supports packet data service in a variety of formats, including support for IPv4 and IPv6. Tier III compliant products were launched in 2012.