About DMR.

DMR, or Digital Mobile Radio, is a digital voice protocol used in amateur radio. It was first developed by the European Telecommunications Standards Institute (ETSI) and is now used by amateur radio operators around the world. DMR uses time division multiple access (TDMA) to allow multiple users to share a single frequency channel, which makes it more spectrally efficient than analog FM. DMR also provides features such as individual and group calling, text messaging, and GPS location reporting. DMR radios are available from several manufacturers and can be used on both licensed amateur radio frequencies and commercial DMR networks.

What about timeslots.

In DMR, a timeslot refers to a specific time period during which a particular user or group of users is able to transmit or receive a signal. DMR uses a technology called time division multiple access (TDMA) to allow multiple users to share a single frequency channel. This means that the frequency is divided into two time slots, and each time slot is assigned to a specific user or group of users. For example, if a DMR repeater uses time slot 1 for voice traffic, then time slot 2 can be used for data traffic such as text messaging or GPS location reporting. In this way, a single frequency channel can be used to support both voice and data communications, which makes DMR more spectrally efficient than analog FM. In addition to this, DMR radios can be configured to use different time slots for different types of communication. For example, a radio can be configured to use time slot 1 for group calls, and time slot 2 for individual calls. This allows for a more efficient use of the available spectrum, and also allows for different types of communication to occur simultaneously on the same frequency channel.

Why are there different networks.

There are different networks because DMR is an open standard, meaning that anyone can develop their own network using the DMR protocol. Each network is operated by a different organization or group of individuals, and they may have different goals, coverage areas, features, or rules and regulations. Some networks may focus on providing coverage in a specific region or country, while others may focus on providing specific features or services. For example, one network may focus on providing emergency communications services, while another may focus on providing access to hotspots for portable operation. Additionally, different networks may have different policies and rules regarding the use of their systems, such as the type of content that can be transmitted, the type of equipment that can be used, or the requirements for accessing the network. In summary, different networks exist because DMR is an open standard and different organizations and groups have chosen to develop their own network using the DMR protocol with their own goals and rules.

If you would like more information please read the transcript of the ARNSW web series by Matt VK2FLY which can be downloaded here