Hello everybody and welcome back to Everything Hamradio! Today we are going to be talking about the last major digital voice mode, Digital Mode Radio. Much like P25, DMR isn’t really used in amateur radio either. DMR is used primarily in commercial radios, but we are going to talk a little about them anyway.
What is DMR?
Digital Mode Radio, or DMR for short, is an open digital mode radio standard defined in the European Telecommunications Standards Institute Standard TS 102 361 parts 1-4 and are commonly used in commercial products around the world. The goal of this standard was to specify a digital system with low complexity, low-cost and interoperability across brands, so people who buy them were not locked into a proprietary system. While this is a noble idea and the goal of interoperability, this ideal didn’t last. Manufacturers took the basic standard and added features to their radios that made it where it wouldn’t work with other brands. Sounds like a typical big business plan to me…
DMR uses the standard of a 12.5kHz channel, much like its counter part P25. The major difference between DMR and P25 is the audio quality. Because DMR splits the 12.5kHz channel into two channels, with forward error correction it only leaves about 2,450 b/s left for a single voice channel. P25’s voice channel is 4,400 b/s. This allows P25 radios to have better audio quality.
DMR is only used on VHF and above, namely 30MHz to 1GHz. While it is said to work at 30MHz, as of late 2015 there isn’t any radio systems that operate below 136MHz. DMR relies on only short burst of interference for it forward error correcting to work properly. It is not designed to work in a radio environment where it will have higher interference times and lower signal strength.
Analog vs DMR
So what is the difference between this digital voice mode and analog FM. The DMR association often claims that DMR has better coverage than conventional analog system do. With forward error correction, this may be true, but only when the signal strength is relatively high. In practice, it is not always the case. When the signal strength drops below a certain point, just like other digital voice modes, it will just drop off and will drop off at a point where analog signal are still fully readable even though there may be some noise in the transmission.
Seeing how DMR uses a split bandwidth that is already half the size of conventional analog transmissions, the audio quality and coverage area is on the loosing side to begin with. If you plan on talking in a very limited area, then DMR will give you better audio sound, but I’m not sure the payoff is worth the cost.
Teirs 1 and 2 were release back in 2005 and is used on just conventional systems. Teir 3 is designed for a trunking system.
Teir 1 products are licensed for license-free use in the European 446 MHz band. In the US, the 446 MHz band is designated for Government use as primary users and Amateur Radio use as secondary users. Knowing this, if a Teir 1 DMR radio is used in the US, it can and has caused harmful interference with licensed users of the bands.
The teir 1 standard provides consumer applications and low-power commercial applications using a maximum of only 0.5 watts!
Teir 2 products are designed for the high-powered, licensed commercial radios in the frequency range of 66-960 MHz. It is designed to target those users who need spectrum efficiency, advanced voice features and integrated IP data services. It also specifies 2 channels in a 12.5 kHz bandwidth.
Teir 3, launched in 2012, is geared for the trucked radio systems in the frequency range of 66-960 MHz. It also has the two channel in a 12.5 kHz bandwidth, but it supports short messages and packet data transmissions.
As we touched on earlier, originally this standard was supposed to be totally interoperable where anyone could buy any brand of radio and it would work with any other brand of DMR radio. This started in 2005, when and Memorandum of Understanding(MOU) was formed with potential DMR supplier like Motorola, Vertex Standard, Kenwood, Icom and a few others.
While the standard does not specify vcoder to be used, the members of the MOU agreed to use a half rate DVSI Advanced Multi-Band Excitation(AMBE) vcoder to ensure interoperability. In 2008, the DMR Association was established by members that signed the MOU to provide a place where information and technology could be shared between the members to maintain interoperability. There are currently approximately 40 members of the DMR Association.
Even though a certain vcoder was agreed upon by the members, the standard allows manufacturers to implement additionally features on top of the standard which has basically left the interoperability function in the dust and now basically doesn’t allow for interoperability between brands.
In this post, we finish up the four major types of digital voice systems. We have talked about DStar and Yaesu System Fusion for the amateur community. We talked about Project 25 or P25, which is used in the Public Safety area and now DMR which is used in the commercial world. In each of the systems that we have talked about, we have talked about the ups and downs of each system and I have noticed one major thing with each of them that I noticed. Every digital voice mode that I have written about doesn’t work with any of the other digital voice modes that I wrote about.
Back in like 2002 or 2003 when the NIMS system was released by Homeland Security, one of the things that it pushed hard was interoperability. Up until digital radio came out, this wasn’t as much of an issue with any band. Unfortunately, now that digital has come around, nobody seems to want to place nice anymore. One of the things that I have always loved about Amateur Radio is the way we work together better than other do. I would’ve thought that if anyone was going to have system that worked together it would be us, but alas even we failed at that. System Fusion doesn’t work with DStar, DStar doesn’t even work with analog.
The funny thing is, the DStar system is open source and any manufacture can use it. So why hasn’t Kenwood or Yaesu or whoever make their own DStar radio? I can kind of understand why Yaesu made System Fusion, because I, personally, think it is better, but why not make a DStar radio anyway.
I am a Kenwood guy!
I have had about 10 radios over my 20 years as a ham. Out of those 20 radios, I have had 3 that were not Kenwoods. My fist radio was a Radio Shack HTX 202, the second was a Icom W32A and the last is my current hand-held a Beaufang. All of my non-Kenwood radios have been hand helds; I’m kind of hard on HT’s.
Now comes the time that I have to change all that. If you read my Yaesu System Fusion post, you will know that my club, in fact my whole county, has gone with System Fusion repeaters. With the functionality that they provide, it only makes sense to goto a Yaesu radio for my next purchase.
I guess that about wraps it up for this post. Thanks for stopping by and checking out my site. If you have not done so already, please subscribe to my site to receive emails on when I publish a new post or podcast. Also, please like me on Facebook and follow me on Twitter. Links to all my social media pages can be found on the menu at the top of the page under Social.
Until next time…
73 de Curtis, K5CLM