DMR vs. C4FM: Choosing between two increasingly popular digital radio platforms
Editor’s note: This article is also published on n2rac.com.
New forms of digital radio are gaining popularity. For example, on the radioid.net database, which is used by the DM-MARC and BrandMeister networks, there are now at least 161,000 registered callsigns, and the number keeps growing at a fast pace.
DX1ARM on digital
For this article, I will focus on DMR and C4FM, since these are the platforms supported by DX1ARM. Here are the assets we have thus far:
- Yaesu DR-1X C4FM repeater deployed in San Mateo, Rizal, operating at 431.600 MHz. This is a hybrid C4FM and analog repeater, which supports Yaesu System Fusion radios.
- Motorola GM-300 with MMDVM board as wireless link, linking our repeater to YSF room number 78427 “DX1ARM”.
- BrandMeister DMR TalkGroup 51518 “DX1ARM” crosslinked to YSF 78427
- Echolink DX1ARM-L, crosslinked to the YSF and DMR TalkGroups
These inter-links mean that when someone is talking on BM TG51518, for example, the traffic is also transmitted to the YSF room, as well as Echolink, allowing for cross-mode communication.
Our DX1ARM UHF ROIP Zello channel receives audio from the digital talkgroups, but cannot transmit, due to the restrictions of the BrandMeister network. Transmit on this channel goes to the analog side of the repeater at 431.600 MHz. Those without DMR radios can use this to get notifications or listen in when there is traffic.
I will focus more on some practical considerations. For the purpose of this article, our comparison includes how you can get into the popular networks like the BrandMeister DMR network, the YSF (Yaesu System Fusion) network, and WIRES-X.
YSF is an unofficial network run on independent servers, while WIRES-X is Yaesu’s own network.
For the comparison, I will go into points below.
- Wide brand availability, which means there is also a variety of price points. Cheapest DMR radios (that are capable to go on amateur networks) are at around PhP 2,500. Higher-end commercial brands include Hytera, Motorola and Kenwood. China-made options include TYT, Retevis, Ailunce, Radioddity (a U.S. brand but made in China), and more! Be sure to go for the ones that are Tier II compliant, which can do TDMA and access Tier II repeaters.
- There is also a secondary market for good DMR radios. In my opinion, the reputable China brands like TYT and Radioddity offer reasonable quality at an affordable price.
- Firmware customizability. Some DMR radios, like the Radioddity GD77, TYT MD-380, MD-390 (and Retevis RT3 and RT8 variants), do support custom firmware, with features targeted at making the radios more flexible for use by radio amateurs. The openGD77 firmware now even supports the Baofeng DM-1801, Baofeng RD-5R, and GD77S.
- Flexible routing. On DMR networks or hotspots, simply key up on a TalkGroup, and you are routed to that TalkGroup. Actually, each transmission has an origin and destination, so routing is defined in each of these. This means you can use other repeaters like DX1BSP or DX1CI and still get routed to the DX1ARM TalkGroup 51518.
- Private calls. Aside from TalkGroup routing, DMR also supports one-on-one routed calls on both simplex, repeater, and hotspot networks.
- Time division multiplication access. On DMR repeaters, two timeslots can be used at the same time, meaning two QSOs can happen at any given time, using the same frequency and network. Most networks use TS1 for internet-connected traffic and TalkGroups, with TS2 for local (non-internet connected) traffic.
- Repeater “wake up” and other “fun” features. When you key up a repeater, your radio actually handshakes to establish timeslot synchronization. It does not transmit until the repeater is confirmed to be within reach. Also, you get other functionalities like text messaging (where supported by the network), remote confirmation, remote-monitor, remote-kill, etc.
- Database of users. This includes not just the callsign, but name and location, as well. Very useful reference when DXing on digital. You will need to regularly update your radio’s database, however.
- Talker Alias. This is a feature supported by custom firmware, which displays callsign and name data for users not in the radio’s current database.
- Last Heard. On some radios, especially those with custom firmware, the radio can display a Last Heard list — basically the caller ID of the recent XX stations received.
- Very active BrandMeister talkgroups. You can go to brandmeister.network to explore the different talkgroups. There is even the “Last Heard” updated here dynamically, so you know which talkgroups currently have traffic and which stations are currently talking.
Drawbacks of DMR
- There is a high learning curve associated with programming “codeplugs” for DMR radios. Aside from frequency, you need to know the color code and timeslot being used by your repeater. You also need to program a destination TalkGroup for your transmissions, thus adding to the complexity.
- With the usual codeplug, for example, you need to have a channel programmed for each combination of frequency and TalkGroup, which can bloat your zone and channel list.
- Custom firmware addresses these drawbacks, however. For instance openGD77 simplifies everything, so that you only have to program in your favorite TalkGroups, associate sets of “TG lists” with a channel, and just scroll to select. There is also a manual or ad hoc TG feature for most custom firmware.
- Numeric user IDs. Sure, I listed the database as a benefit earlier. But it can also be a disadvantage. Most lower-end radios support only a few thousand database contacts. And you do have to regularly update your database or recently-registered hams will only appear as a number.
- You need to register to the common userID registry at radioid.net before you can get on the air on DMR, both on simplex, hotspot, and repeater.
- DX1ARM does not have a DMR repeater. You can either use your own hotspot or get on the air using another club’s repeater with dynamic TalkGroup support (such as DX1BSP or DX1CI).
- Our very own C4FM repeater. DX1ARM has a UHF repeater that runs System Fusion. This simplifies getting on air on digital whether local or for TalkGroup use.
- Simple programming. Just key in your callsign, and program the frequencies (in Greater Manila Area, it’s 431.600 + offset) and you’re on the air. You can basically get on the air without the need for a computer.
- There is support for WIRES-X, although our repeater link is currently not connected to the official WIRES-X network. We do have YSF.
- Well-built radios. Yaesu is known for the quality of its radios. A bit pricey, though.
- Messaging through WIRES-X. A bit complicated, though, but ideally something that can be used to exchange messages across rooms, nodes, and radios. This can also be done through APRS support with some radios.
- Auto-Mode Select or AMS. This means your radio can receive both analog FM and digital C4FM traffic from our repeater, and switch across automatically. DMR radios only support one mode at a time, although these can be set to auto-scan across several channels.
Disadvantages of C4FM
- Radios are more expensive. Cheapest radio is the Yaesu FT-70DR portable, which retails at PhP 9,500.
- Basic routing. With C4FM, it’s just like analog, wherein your transmission is routed at the server/link level, unlike DMR, wherein TalkGroup can be defined on each transmission.
- Basic information displayed. With C4FM, the only information displayed on the radio screen is the callsign and (with radios that support GPS) the distance.
- You are locked into proprietary technology. C4FM is essentially P.25 digital technology, although it’s the Yaesu implementation. It is not likely that the tech will be licensed out to other manufacturers. Yaesu is actually very aggressive in marketing its technology, to the extent that it provided steep subsidies to repeater purchases by clubs, to prompt use.
Getting on the air
Contrary to what many think, being able to QSO on both DMR and C4FM platforms will not necessarily require a hotspot or repeater. Simplex works! However, for me, one of the advantages of digital is the ability to route your traffic to the network, so you can have a wider reach.
WIRES-X has the concept of nodes, which are C4FM radios connected to the computer and to the WIRES-X network.
In the context of DMR and YSF, this can be done through links. Or, it can also be done through hotspots. Consider how your hotspot can be your own personal “repeater” that connects you to the network of other DMR or C4FM users.
DMR has its concept of TalkGroups, which are numeric groups where traffic is routed to. When you connect to a talkgroup, you are essentially listening to all traffic sent to that talkgroup. Here is a list of DMR talkgroups and their short descriptions. Here is the TG51518 or “DX1ARM” page.
BrandMeister Philippines is the Core Team of Filipino hams who manage support for the local network and resources. We actually have a BrandMeister Master Server in the country.
YSF users, meanwhile, connect to “Reflectors” which are hosted on servers. Here is a list of YSF Reflectors.
Note that it is much easier to switch TalkGroups on the DMR network than switching YSF Reflectors. With a DMR radio, you can simply change channels (or TalkGroups), then key-up with the PTT, and you are instantly connected to that TG.
With YSF or WIRES-X, this can be either done from the WIRES-X menu, through numeric input, or by going to your hotspot/repeater interface and selecting another YSF Reflector or server.
DMR and C4FM are distinctly different platforms, but our goal is the same — to be able to connect, converse, and converge. It can be a highly personal choice, although you can also choose to have both technologies within reach.
In most cases, the sets of people who converge on either the DMR or C4FM networks might be different. In some cases, there are crosslinks that allow access to both (such as with our TG51518 and with the PARA TG51588). With DX1ARM, we do have the best of both worlds, being accessible from both the BM DMR network and YSF network. If you don’t have a digital radio yet, you can, of course, QSO through Echolink at DX1ARM-L or listen to the live feed at the DX1ARM UHF ROIP Zello channel.