A Powerful Alternative for DMR Hotspots with OpenGD77

There are Hotspot devices that help Amateur Radio operators who use DMR. A great convenience if there is no DMR repeater relay nearby. However, it can only be used up to a distance of 100 meters. A system that costs almost the same as a handheld radio with OpenGD77 installed but provides access to a much wider area can be established.

Amateur Radio is a hobby with a wide range of applications. Dstar mode, one of the digital modulation types that has been used for years in the short-distance radio-related part of this hobby, especially developed for amateur radio operators, did not attract much attention due to the expensiveness of the devices produced. Digital close-range communication systems, which have not progressed much over the years, were used by a very small segment of amateur radio operators.

What is DMR?

Digital Mobile Radio (DMR) is a digital communication system that has become very popular among both amateur and professional radio users in recent years. There are many factors behind this popularity, and let's list some of them, especially those that are quite attractive for Chinese manufacturers.

DMR technology is relatively simple, which reduces production costs. This allows Chinese manufacturers to bring DMR radios to market at more affordable prices.

It is an open standard, meaning there is no obligation to pay licensing fees or patents. This makes it easier for new manufacturers to enter the market and increase competition.

It offers clearer sound quality than analog radios. This makes it possible to communicate clearly even in noisy environments.

It can be used not only for voice communication but also for data communication. In this way, text messages and GPS coordinates can be sent via radios.

There is wider coverage than analog radios. This is especially useful when communicating over rough terrain or inside buildings. Thanks to networks such as Brandmeister over the Internet, amateur radio operators communicate with each other across cities and countries, wherever they are in the world.

All the advantages it offers have made DMR very popular among amateur radio operators. Especially the introduction of affordable radios has brought this system to wider audiences. Amateur radio operators use DMR to perform QSOs (Radio Communications), establish emergency communications, and communicate with local and global talk groups.

If you have it and you can reach it with your radio, you can make calls with DMR radio via amateur radio repeaters in your city. If you do not have such an opportunity, you can set up a Hotspot to connect the radio to the DMR network for use at home. 

What is MMDVM Hotspot?

MMDVM (Multi-Mode Digital Voice Modem) is a combination of software and hardware that allows amateur radio users to use digital modes such as DMR, D-STAR, P25 and C4FM. MMDVM is usually installed on a Raspberry Pi or similar minicomputer. MMDVM allows you to use digital modes by connecting to your radio device over the internet and communicate with other amateur radio operators around the world.

Hotspot consists of two components. One of these is the Raspberry Pi computer card, and the other is the hat or in English: Hat card, which enables wireless communication.

This device can be purchased in parts and assembled, or it can be purchased as a whole, adjusted and used.

If more than one radio operator in a neighborhood wants to use the same MMDVM Hotspot, the 10 milliwatt power of this device is not enough to communicate more than 100-150 meters away. Therefore, as a good alternative, the communication distance can be increased with a handheld radio with OpenGD77 software installed on it. Such as GD-77, GD-77S, DM-1801, DM-1801A, RD-5R, MD-9600/RT-90, MD-UV380/RT-3S, DM-1701/RT-84 and MD2017/RT-82 devices can be used for this job. Since it was the easiest and cheapest one to find, Baofeng DM-1701, I chose it.

(The operations described here require extremely good computer and radio programming knowledge. If you are not careful, there is a possibility of damaging the device. Do all these operations knowing this. By doing what is explained here,  you are deemed to have accepted in advance that you will be responsible for any bad situations that may occur.)

But be careful! Since the chipsets of the new 2022 version Baofeng DM-1801, DM-1801A devices sold with the same model number have changed, this firmware cannot be installed on new devices sold with this model name! Pay attention to this issue when purchasing.

You may be thinking, what does handheld radio have to do with it? It has two advantages. The costs of the system using a handheld device and the system using MMDVM Line are very close to each other. Depending on the location, the domain can be accessed from miles away.

If you buy it domestically, the fully assembled Hotspot-MMDVM is sold for around 4400 TL. Even if you buy it from Aliexpress, it costs about this much.

If you want to buy MMDVM-Hat individually from Aliexpress, it is sold for 770 TL. 

On Aliexpress, MMDVM Line and its box and fake antenna cost around 1100 TL including tax.

Hotspot costs between 2600-3000 TL.

Now let's look at the cost if we install OpenGD77 on the handheld device and buy a Raspberry Pi, box and SD card.

Baofeng DM1701 model is sold on Aliexpress for around 1400 TL. You can look at this link . Don't forget to take the programming cable too! With that cable, the device is connected to Raspberry Pi Zero.

With tax, the device costs around 2200 TL. However, you must have an amateur radio license when purchasing this device! Since it is easily checked in the system via your TR ID number, it can be stuck at customs if you do not have a document!

When you buy a Raspberry Pi Zero W from Turkey, it costs around 600 TL. It would make sense to buy a box for the Raspberry Pi. You also need to buy a 16GB SD card to install the program. If you have it, an 8GB SD card will also work. 

Baofeng DM1701, Raspberry Pi Zero W, Raspberry Pi Box and SD Card cost around 3000 TL in total. With the calculation above, it is the same price as the Hotspot device, maybe even cheaper. Especially if you try to buy from Turkey, Hotspot is sold for up to 5000 TL!

radiosification Youtube Channel explain how to install the program  at https://www.youtube.com/watch?v=N60ho7SQ48M . You can handle it from there, you will select opengd77 as the modem and do not select anything as the screen type. Necessary information can be seen on the screen of the radio with Opengd77 firmware installed. 

When using OpenGD77, the Pi-Star power setting of the connected device is made by changing the "RF Level" setting under the Modem section in the MMDVMHost section on the Pi-Star Digital Voice - Expert Editors page in the Pi-Star Configuration section. In the table below, you can see which value corresponds to which output.

50mW	1
250mW	5
500mW	10
750mW	15
1W	20
2W	40
4W	80
5W	99

Attention! If I were you, I wouldn't exceed 500 milliwatts. If it is left on in a group where people are constantly talking, the device gets very hot and the battery drains quickly! With a good external antenna, this power will be sufficient.

Uploading Firmware to Baofeng DM-1701

I downloaded the necessary files from the link given by the seller on Aliexpress from whom I bought the radio . Therefore, it would be better to scan the files with a virus software and check them. 

Software required to add, edit, save, and load firmware on CPS channels. When the file opens and asks for a password, type R2023.09.21.01. Windows 11 creates problems installing its drivers. Therefore, you'd better do it with a computer with Windows 10 or below. It happens in Windows 11 too, but it's hard!

This picture shows how to choose the type of radio. Use the option below, exactly as shown.

Select Firmware Loader from the Extras section. 

In the window that opens, first select DM-1701 / RT-84 under Radio Type. Then click the Select official firmware (donor) file button at the bottom right.

In the window that opens here, click on the MD9600-CSV(2571V5)-V26.45.bin file.

With the device turned off, plug its cable into the computer and your device. Turn on the radio by pressing the latch (PTT) and the button above it at the same time.

In the open window, press the Select Open Firmware & Update button at the top right. Double-click the OpenDM1701_20230915 folder.

Find the OpenDM1701_20230915.bin file and click on it. 

The green bar moves from beginning to end and Settings Updated  appears on the radio screen .

So, OpenGD77 software has been installed on your device. If you are going to use it as a hotspot, plug the programming cable into your device and plug it into the left micro USB output of the Raspberry Pi Zero W with the OTG adapter. Connect your 5 volt adapter to the right port of Raspberry Pi Zero W. If everything is OK, your hotspot covering a wide area will work. You can keep the device on the charging bed. Instead of using your own antenna, choose a roof antenna. I read that if you use it with its own antenna, Raspberry Pi Zero W will be affected due to RF. I used it with its own antenna and there was no problem. Then I plugged it into the external antenna. 

OpenGD77 User Guide can be viewed at this link . In fact, OpenGD77 Firmware is much better than the original software installed on the handheld radio. There's even a spectrum mode. In other words, the device becomes extremely useful. You can prepare and use channels with the CPS program. There is no need to program channels for the hotspot. Pi-Star performs the necessary control function beautifully.

You need to make a simple setting on the radio.

Green Menu Button > Options > General options > Hotspot > (with the channel switch selector next to the volume) select MMDVM and release it.

If you are going to use BlueDV on your Windows computer, there is also a BlueDV option.  https://www.pa7lim.nl/bluedv-windows/

If you have done everything correctly, DMR and DMR Net connections will appear green when you connect to Pi-star via your Web Browser. If you cannot connect even though the device MMDVM setting is correct, you can try different servers as DMR Master. You must have entered a password for Hotspot Security on Brendmeister. If you do not enter the same password on Pi-Star, you cannot connect to the network.

You can use TG222997 to test whether your voice is transmitted through Brandmeister. This is a parrot system that repeats what you say when you talk (if you are using the Bulgarian server, reach the parrot via TG284997).

I hope you like it.