Understanding the High Playability of MMDVM in Amateur Radio

Hello! Everyone, this is BD4SJY! It seems that everyone is really interested in amateur radio, so let’s share about MMDVM, which is quite common and has high playability in amateur radio.

Before we start, since this article requires a certain level of basic knowledge, I recommend that beginners understand clearly before trying! As always, I will try to provide solid content and minimize professional jargon, offering some easy-to-understand examples. If you have any questions during the actual operation, feel free to leave a message and I welcome all enthusiasts and experienced HAMS to share their insights! Now, let’s welcome today’s protagonist~

MMDVM box and Motorola R7 & SL2M handheld radio

Let’s start with a professional definition: MMDVM (Multi-Mode Digital Voice Modem) is a multi-mode digital voice modem initiated as an open-source project by UK HAM G4KLX, following the GPL v2 license. It aims to be an open-source multi-mode digital voice modem capable of performing functions of ARM processors and simple analog interface boards. MMDVM comes with an RF circuit board that serves as an internet radio gateway, processing all amateur digital voice modes, converting analog radio into digital radio.

To translate for everyone: Through MMDVM, various digital modes of radios can quickly connect to the internet, achieving interconnectivity across regions. In the previous article, many digital modes were discussed, but due to manufacturers’ interests, various digital modes cannot interconnect. Additionally, the communication distance of radios is quite limited. However, with MMDVM, interconnectivity across devices and regions becomes possible.

7-inch MMDVM box

Let me give you an example: A has a DMR mode digital handheld in Hainan, and B has a C4FM handheld in Xinjiang. First, their handheld radios cannot interconnect due to their different digital modes, and second, they are too far apart to communicate directly through their handhelds. At this point, A and B each have an MMDVM box, and their boxes connect to the backend server via the internet to exchange their handheld information, which is then decoded and sent to each other’s handhelds as sound. In short, it is about interconnecting the signals of two handhelds through the internet.

Schematic

Structure: The structure of MMDVM is actually quite simple. The most common combination is a hotspot board + Raspberry Pi. You might be confused at first, so let me explain. The hotspot board receives and sends radio signals, while the Raspberry Pi acts like a small computer motherboard, where the Pi-star system is installed. It can convert the signals received or needed to be sent by the hotspot board into data, and then send the signals to the backend server via the internet, allowing communication to take place.

Internal structure of MMDVM

Some might ask why there are large and small boxes. Many HAMS like to assemble their own devices, while some, like me, prefer to buy ready-made ones. The size of the box depends on the screen size, the number of batteries, whether it integrates a wireless network card, etc.

The above briefly introduced the principles and components of MMDVM. Next, let’s talk about how to use the MMDVM box to achieve communication.

1. Preparation

① Equipment: You must have a digital mode device at hand, which can be handheld or mobile. The mode should be one of the mainstream modes introduced in the previous article. If you are unsure, refer back to that article.

Then you need to have an MMDVM box. If you enjoy researching and have good hands-on skills, you can find some related materials and buy components to assemble it yourself, which is a lot of fun. If you, like me, prefer convenience, you can choose to buy a ready-made one online. These devices are usually assembled by enthusiasts with 3D-printed shells or you can buy a ready-made box for modification. The market is quite complex, so it’s important to find a responsible and patient seller who can guide you, so be cautious when purchasing and avoid blind purchases. Here, I would like to give a shoutout to my mentor BH4THI, who is highly skilled and does everything himself. If you need help, you can search for BH4THI in the seafood market.

② Account: Apply for an international ID, starting with 46 in China. The prerequisite for applying for an international ID is that you have already obtained an A-class operating license and have a call sign, as these two documents must be uploaded as attachments during the application. For details, please refer to the portal.

BM website account application is necessary for the servers we need to use behind our devices. The registration content is as shown below:

BM website registration reference

The above is all the equipment you need to prepare and the accounts that need to be registered in advance. Without any of these, you cannot use MMDVM properly. Next, let’s talk about who we can communicate with using this box. Finally, we will discuss the relevant settings.

First, we need to know that DMR communication is one of the modes in radio, and its settings are based on radio frequencies. We will still take Wuxi digital relay as an example. The official published data is shown below. Let’s interpret it together. First, we need to create a digital channel in the device, which must be in DMR mode because the relay is DMR mode. The receiving frequency is 439.350, and the transmitting frequency is 431.350. This has been mentioned before regarding the offset. The color code can be understood as the sub-audio code of the analog signal, which is a fixed value, so just choose according to the official information. The time slot for DMR has two, 1 and 2, referred to as dual time slots. You can understand this as a dual lane; traditional analog channels are single lanes and can only accommodate one signal. Here we have two lanes, allowing two groups to speak simultaneously without interference, greatly improving the relay’s efficiency. Now looking at the last two groups, 46001 and 460510, we can understand them as two groups. 46001 is the ID of the China DMR group, and as long as you join this group, you can chat with everyone, and they are mostly locals, with almost no international friends. Of course, it doesn’t exclude international friends from visiting the group. 460510 is the Wuxi group, where local enthusiasts are located. Therefore, if we are using the Wuxi digital relay, we need to store the group number in the address book, such as receiving frequency 439.350, transmitting frequency 431.350, color code 9, time slot 1, and set the contact group to 46001 (China group). Since Wuxi’s relay is connected to the BM server via the internet, when we speak on this frequency, all radios connected to group 46001 can hear us. For example, receiving frequency 439.350, transmitting frequency 431.350, color code 9, time slot 2, setting the contact group to 460510 (Wuxi group), if I go on a business trip outside and have left the coverage of the local relay, I can use my MMDVM to set the backend BM server group to 460510 and then use the handheld to forward to the BM server, which forwards to the Wuxi relay, and then the Wuxi relay broadcasts to the radios within the coverage area on frequency 439.350, transmitting frequency 431.350, color code 9, time slot 2. You can also understand the digital relay as a larger MMDVM box placed at a higher location. So besides 46001 (China group) and 460510 (Wuxi group), there are many other groups. For example, 91 (world group) where foreign friends occasionally log in. 460319 (Xingtai group) is also quite active. This is a group where you can find people to chat with; it’s not a one-on-one communication, everyone in this group can hear each other. This is the fun part of MMDVM; as long as there is internet, there are no restrictions on location or time, you can find people from thousands of miles away to communicate.

Wuxi digital relay parameters

Next, let’s talk about how to set up the MMDVM box and the relevant configuration on the BM website.

When we receive the box, regardless of the model, if the local network isn’t configured, it won’t connect automatically. So after turning it on, wait for a few minutes; if the box cannot find the network, it will open its own hotspot. At this point, we connect our computer to its hotspot signal, which is unencrypted. We can check the IP address on the box and enter it in the browser. Since I am already connected to the internet, I won’t demonstrate the steps to connect to the hotspot here.

IP Address 192.168.2.135

1. After entering the webpage, we see this screen. Click on the configuration in the upper right corner:

Login page

2. Log in to the system with the default username pi-star and password raspberry, then click confirm to log in.

Enter account password

3. For new machines, first configure the WIFI by clicking the arrow.

Add WIFI

4. Enter the WIFI username and password; do not use Chinese names as the system may not recognize them. I usually set one for home and another for mobile hotspots for convenience when going out. Then click SAVE to save. After saving successfully, it will automatically connect to the saved WIFI information the next time it starts up. As long as the computer is connected to the same network as the box, you can log in to the backend system by entering the IP address directly.

Configure WIFI

5. General configuration: Here, the items to be checked include our call sign, international ID, and the transmitting and receiving frequencies of the box. After setting these, be sure to remember the transmitting and receiving frequencies for setting up the handheld.

Setting instructions

6. Below are DMR configurations, Hotspot Security. Here you set a purely numeric password, which you must remember. If you can’t think of one, 1234567890 will do. ESSID can be anything, as when we have multiple devices, we can add different suffixes to distinguish between them. Choose color code 1; it doesn’t matter. After everything is changed, click to apply settings. At this point, the MMDVM box is set up.

Next, let’s take a look at how to set up the BM backend.

1. Log in to our BM account website, click on SelfCare on the left side. Do you remember the Hotspot Security we set in the box? Or the suggested 1234567890? Fill it into the box below and click save.

Hotspot Security settings

2. Do you remember the ESSID mentioned earlier? Select the corresponding device number on the left, and you will see two boxes on the right, one for time slot 1 and one for time slot 2. Here we can set which static group to add to time slot 1 and which to add to time slot 2. Manually input into the left box, click the arrow to save, or delete with the left arrow. I have added 46001 to time slot 1 and 460510 to time slot 2. You can also add local groups or the 91 global group to hear how foreign friends communicate.

Static group settingsBox display after settings are complete

Now our MMDVM box is completely set up. The two time slots will work simultaneously, with the first time slot allowing communication in group 46001 and the second time slot allowing communication in group 460510 Wuxi. Finally, let’s see how the radio should be set up.

HP780 setup instructions

As we can see from the image, the receiving and transmitting frequencies match those set in the box, with time slot 1, color code 1, and the contact set to 46001 national group. Save it with a name like National Group. As long as our box is powered on, the handheld can communicate with the friends monitoring group 46001.

MMDVM box and Motorola R7

In closing, if there are any unclear parts, feel free to leave a message. Also, it’s important to remember to comply with laws and regulations during communication. Do not violate rules or disturb others. This article may be a step closer to the basic knowledge compared to previous ones. Some may still be new to this, but I believe that as long as there is interest, this article can help those in need.

(Source: Walkie-Talkie World)