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DMR FAQ's

What are Color Codes?

Color Codes are like Network Access Codes or PL (CTCSS) tone access. Each DMR repeater can have one of sixteen different Color Codes.

What are Time Slots?

With a TDMA (time division multiple access) system like DMR, the mobile or portable radios are synchronized typically by a repeater and assigned a time slot. In DMR Tier 2, there are two time slots, i.e. 2-slot TDMA. A mobile radio transmits for 30 milliseconds and then receives for 30 milliseconds. It listens for a permission to transmit and then begins a call to all other talk group members who will also receive on that same time slot, e.g., Time Slot 1. Meanwhile, a different group of users on another talk group could be using Time Slot 2 simultaneously. Well almost simultaneously, offset by 30 ms., but you would never know the difference, because two voices can come out of two radios simultaneously from the same repeater.

What are Talk Groups?

Talk Groups are like different work groups that you communicate with. They are programmed as "channels". Several can share a Time Slot on a repeater like multiple PL codes can share a community repeater. Each talk group can be isolated from the other, but you may get a busy tone if the same time slot is in use by another user on another talk group. Greater efficiency can be achieved by bridge routing and trunking techniques. Each radio can have more than one talk group and may scan or roam based on talk group.

Which Talk Group should I be using?

There are more than 100 talk groups available to the amateur DMR community, however not all repeaters carry all talk groups. Some serve clubs, some are topic specific and some are geographically based. There are approximatley 33 talk groups on a worldwide basis. In general, the talk groups are divided along geographic lines and / or a language specific basis. Historically the geographic talk groups have been limited to the repeaters and c-Bridges within a specific region. The reason for this was not to exclude folks from speaking to other regions, rather, they were used as a tool to better manage network resources.  The DMR admins ask that users respect the intended use of each talk group and utilize the systems so that the minimum amount of resources are used on each transmission.

Minimal Use

This is an important concept but what does it mean?
Let’s say a user in Europe was looking to communicate with someone in North America, the way to accomplish this would be to use one of the global talk groups, Worldwide Calling or Worldwide English Calling. (or another language calling group.) But if this same user was only trying to speak to a friend and both of them had access to their local repeater it might be best to use that repeater’s local channel. In the case of making a call to North America on one of the Worldwide Talk Groups, the transmission is keying up one timeslot on nearly every amateur DMR repeater in the world. In the case of speaking to a friend on the local talk group, you would be having a conversation but only using one timeslot on one repeater. Although possible, it would not make sense to have the local conversation on the Worldwide Talk Group because you would use far more resources than necessary and those resources would be unavailable to the thousands of other DMR users around the globe. Make sense? So with a best practice of "Minimal Use", you would try to use a talk group that both users have access to that would key up the least amount of repeaters during your communications.  So, the kind of talk group to use would be in the order of: Local -> PTT -> Regional -> National -> Worldwide.

Calling Talk Groups

Most of the National and Worldwide talk groups, such as NA, WW and WW English are considered "calling talk groups". These talk groups are not intended for you to have a lengthy QSO, rather, they are for calling someone and making contact, then you are expected to take your QSO to another talk group that both of you have in common, but one that uses less resources, such as one of the PTT talk groups. (See "PTT Talk Groups", below.) Once you have made contact on a National or Worldwide talkgroup, don't forget that you are keying up a lot of repeaters - with the concept of "Minimal Use" you should move your communication off to a talk group that will key up less repeaters. Now if, and that is a big if, you only have a calling talk group in common with the other party, then of course you can continue your conversation - but be forewarned, someone is likely to start playing "DMR Police" and might come up on that talk group to tell you that you should not be having a lengthy QSO on that talk group. Just politely (and briefly) explain that this is the only talk group that you both have in common and that should suffice as an explanation.

PTT Talk Groups

There are some talk groups that are considered "on-demand" or "PTT" talk groups.  These are only heard on a repeater after a user "kerchunks" the repeater on that talk group.  This activates the talk group on that repeater / timeslot, and allows you to hear the activity on it.  This is another great way to have a conversation with someone without keying up a lot of regional, national or worldwide repeater resources. The talk groups TAC310, TAC311, UA WW, UA English WW, and UA NA are just some examples of these kinds of talk groups. (UA = User Activated.) Almost all repeaters carry some (if not all) of these PTT talk groups.

How does the network work?

Generally, networks can be created by an IP Site Connection between two or more repeaters. MotoTRBO's IPSC protocol communicates Peer-to-Peer. Usually there is a Master and up to 15 Peers in each IPSC. Multiple IPSCs can be bridged together on each talk group and routed to different destinations.

How many Amateur DMR Networks are there?

More than twenty. Go to: http://dmr-marc.net/FAQ.html and scroll to the bottom of the page for a sampling.

What radios can roam?

Generally speaking, all the Motorola high tier mobile and portable radios (XPR4550, 5550, 6550 and 7550).

How does Roaming work?

The radio will look at the RSSI (Received Signal Strength Indicator) from each site in its list on a specific talk group and select the strongest site to receive and transmit on.

Isn't that like scanning?

No. Scanning will select a signal, regardless of signal strength, as long as it breaks the squelch threshold. However, scanning can also accommodate more than one talk group and multiple analog channels.

How is this different from D-Star?

DMR is the ETSI Standard, Multiple Vendors, TDMA 2-slots

Is this just a Motorola technology that is being pushed into the ham community?

NO. There are multiple manufacturers: Connect Systems, Kirsun, Tait, Vertex, Motorola, Hytera, Simoco and perhaps Yaesu. Kenwood has just announced DMR models for Europe.

Will your repeaters interfere with existing 144 or 440 analog repeaters?

No. Normal Frequency Coordination is required, but DMR Emission Bandwidth is 7.6 KHz. Normal UHF channel spacings are 12.5 KHz also VHF are 10 KHz.

Will your radios also support legacy analog operation?

YES.

Where can I buy this stuff and how much does it cost?

There is a Ham Friendly Dealers list on the DCI website, http://www.trbo.info/dci/hamfriendlydealers.html

Where do I get programming cables and CPS software, and why can't I do front panel programming?

Motorola Dealers, eBay suppliers and Motorola on Line (MOL). FPP is available from a 3rd Party ham.

If DMR is so great, why aren't Kenwood, Yaesu, and Icom on board?

Yaesu has alluded to plans to enter the Amateur DMR market on their website and Kenwood has announced DMR models for Europe.

Can I select specific groups or reflectors with DMR?

Yes, DMR has a capability to have Talk Groups which can be local, statewide, regional, national or world-wide via the IP Site Connects, cBridges and SmartPTT servers.

Can I have my location reported into APRS.fi?

Yes, there are several systems doing this now on local and regional networks.

Can I connect my Vertex DMR repeater into the DMR-MARC network?

No, Vertex repeaters do no support IP Site Connect.

Can I connect my Hytera DMR repeater to a MOTOTRBO repeater network?

No, Hytera has an IP Site protocol which is incompatible with DMR-MARC.

How many Talk Groups and/or Channels can I have in a MOTOTRBO radio?

Up to 1,000 Talk Groups or Channels can be programmed into the 4550, 5550 and 6550 radios. The 3500 series can have 500 Channels.

Why don't all stations show callsigns on the radio display?

The DMR radios have a frequent user alias look-up that is similar to a cell phone contact list. Common callsigns can be downloaded and programmed into the radio or added manually, just like a cell phone.

Why do I need to get an ID assignment?

DMR IDs are like phone # assignments. You program it into your radio. Then, others will see you show up on their displays. The assignments are logical and follow GSM numbering protocols.

Who do I get my ID # from?

Go to www.DMR-MARC.net and click on "CONTACT US" on the menu.

Who is DMR-MARC?

DMR-MARC is the group that is coordinating ID assignments world-wide.

Is the range on DMR equal to or better than analog?

We are seeing equal or better coverage with DMR compared to an analog repeater at the same location and antenna. Certainly with better quality audio when in fringe areas.

Is battery life really much longer with DMR?

Yes, battery life is increased by 40% compared to analog FM or FDMA radios. That is due to TDMA transmit and receive cycle durations being half normal power usage times. Fourteen (14) to sixteen hours (16) of heavy usage is not unusual.

Does DMR have the R2D2 digital breakup in fringe areas?

NO. DMR signal fading is minimized using CRC and FEC algorithms AND re-sync time is faster after leaving and restoring coverage. Audio Quality is markedly better.

Is there just one network option?

NO. There are many DMR networks, e.g. DCI, TRBO-6, NorCal, DMR-MARC, CMEN, NC-PRN, Lonestar, GA-TRBO and other Statewide and Regional networks. Build your own and/or use all of the above.

end faq


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