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DMR Information Page
Thanks to a generous donation from MARC Club member Rick Dice, KG8DQ, the Massillon Amateur Radio Club has accepted ownership of two DMR Repeaters here in Stark County.
One is permanently installed at the tower site owned and managed by MARC at the same location as their two meter repeater on the West side of Massillon. It will operate under the club callsign W8NP. The frequency is 442.1125 + Mhz.
Our second system is in beta testing and is
located at a temporary site just west of Alliance and is intended to serve
eastern Stark County while the search for a permanent home. The frequency is
444.7875 Mhz and is also using the club call W8NP.
Our DMR Repeater System is part of the Brandmeister Network, a system comprised of over 1,300 repeaters and more than 3,000 hotspots across the globe and growing everyday.
Brandmeister is tailored to the Motorola TRBO technology and allows for DMR Repeaters to connect worldwide via the internet and link systems together by utilizing organized Talkgroups.
What is DMR
DMR stands for Digital Mobile Radio.
There are several modes of digital communication being used in Amateur Radio
today. DMR is the most popular because of the availability of equipment (new
and used), low price of equipment, the largest network of repeaters and nodes in
the world, and superior sound quality.
If you are a tech junkie, like me, and would like more detailed info, read this whitepaper. It is one of the best I've read. LINK HERE
How does digital communications work
When you talk on an analog radio, your voice is modulated and sent across a frequency. Digital works the same way except your voice is sent through a device called an analog to digital (A/D) converter and the data is then modulated and sent across the frequency. The biggest advantage of digital is the network. When radios, nodes, or repeaters are networked together (usually across the Internet) our range of communication becomes virtually unlimited.
What is a DMR network
A DMR network is a group of repeaters and/or nodes connected together across the Internet. These networks are the real magic behind long distance VHF/UHF communications. When you key up a repeater that is linked to a DMR network the repeater acts like a regular repeater (retransmitting your communication), but also sends your voice to the network, along with some other data, such as time, Time Slot, and TalkGroup information. if the network recognizes the TalkGroup as one that needs to go across their network then it is also transmitted, through the Internet, to thousands of other repeaters and nodes.
There are several DMR networks but the two most popular are Brandmeister and MARC. MARC is a network of ONLY repeaters and ONLY Motorola repeaters. This keeps the communication very clean but also severely limits the people who can communicate on the network. Brandmeister allows all types of nodes, including repeaters (all DMR regardless of manufacturer), digital interface boards, and linked radios. Brandmeister is the largest DMR network in the world and is the one we use.
What are the terms I need to know
In analog communications, only one conversation can take place on one frequency. With digital, multiple conversations can take place on the same frequency. The frequency is divided and the portions are labeled based on the type of division. In DMR, which uses TDMA, they are called TimeSlots. In Ameteur DMR, each frequency is divided into 2 TimeSlots, TS1 and TS2. Each TimeSlot can have a conversation going on at the same time without any interference with the other. This is similar to your cell phone. Although many conversations are happening at the same time, on the same frequency, none of them interfere with the other.
TalkGroups are like CTCSS or DTS codes in analog communications. Let's look at an example. Let's say there are two groups of people talking on an analog repeater and both groups are using CTCSS encode AND decode. Group one is using CTCSS code 110.9 and group two is using CTCSS code 133.8. When someone from group one is talking, everyone in group one can hear them but no one in group two can. Likewise, when someone in group two is talking, only the people in group two can hear them. If both groups transmit at the same time, they will interfere with one another.
TalkGroups work the same way except that they act differently on the repeater than they do on the network. If the two groups, on the repeater, attempt to transmit at the same time they will interfere with one another (in theory, but all DMR radios offer a function to stop this from happening). However, on the network, thousands of TalkGroups can communicate at the same time. This is why we have so many TalkGroups, even though the repeaters only have two TimeSlots. This is a way to organize thousands of communications based on the locality, and content of the conversations. One big difference in DMR is that TalkGroups are required in DMR and are only an option in analog.
When frequencies carry digital information, they can be divided to carry multiple conversations. This is possible because data is encapsulated at one end and then unencapsulated at the other end and each byte of data has a "label" to let the receiving end know where it is intended to go. All of the data can be sent and received at the same time because the receiving end looks at the label and sends the right conversation to the right destination.
Think of it like shipping items. In analog, each item going from Cleveland to Chicago would be unpackaged and need to be in its own truck so that it doesn't get confused with other items going to Chicago. In digital, all of the items can be shipped on the same truck because the shipping end boxes up each item and labels it so it can be delivered at the other end. The receiving end reads the label, on each item, and knows where it goes, without getting it confused with the other items.
TDMA stands for Time Division Multiple Access. Without getting too technical, this where the data is clocked based on time. If you've ever used a 555 timer chip, then you know that data can be sent on the uptick or downtick of the changing clock pulse. Similarly, in TDMA, the data is sent based on the timing of the signal. This is the technology used in DMR, DSTAR, and NEXEDGE
CDMA / FDMA
CDMA stands for Code Division Multiple Access and FDMA stands for Frequency Division Multiple Access. These are basically the same thing but the cellular industry calls it CDMA and the two-way radio industry calls it FDMA. This is when the data is clocked based on frequency. This is the technology used in Fusion and P25
Codeplug is a fancy term we use for the information in your radio saved to a single file. Most hams have been using codeplugs since long before digital radios, we just didn't call it a codeplug. Back when radios first became computer programmable we would install a program that came with our radio, enter all the repeater and simplex information and then upload it to the radio. This is the same thing we do with DMR radios except, because of the large amount of information needed in a DMR radio, most radios require that the programming be done through a computer and honestly, it would be a lot of work to do it from the keypad.
In order to use DMR you will need a DMR Radio, either a handheld or a mobile. Regardless of your radio, it will require a Code Plug which will contain the programming for your exact radio including the active frequencies in use. Most recent code plugs contain all frequencies currently used in the State of Ohio including our two new repeaters in Stark County.
To facilitate this effort, the ARRL's Ohio Section Website now contains code plugs compatible for most popular radio's in use today. These code plugs require a computer to load the program into the radio and a suitable program cable.
Use this link to see the current code plug selections. We can provide assistance to help you program your radio. If you are new to DMR operation, you will need to obtain a DMR ID Number. This ID Number can be obtained from www.radio.net.
Repeater Location - Mercy Medical Center
Frequency - 444.7875
Color Code - 7
TS1 - Local communications (NE Ohio)
TS2 - All other communications
Repeater Location - Alabama Ave SW, Massillon, OH
Frequency - 442.1125
Color Code - 7
TS1 - Local communications (NE Ohio)
TS2 - All other communications
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|last reviewed/updated on 02/04/20|
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