BI7JTA Written, Xu Mingsheng Edited
This Chinese tutorial is an improvement of the English tutorial (Google Blog). The hotspot board from this blog has been verified by countless HAMs worldwide and works perfectly, so you can buy it with confidence! Disdain for some shameless cloned boards that copy for profit, do not adhere to open-source rules, and do not conduct any testing or improvements. Choose wisely! Additionally, it is not recommended to share analog and digital modes as there are many shortcomings. In the case of non-professional repeater modifications, digital and analog cannot operate on the same frequency, and RX/TX must be reversed to free up channels, which is very impractical. This increases the complexity of handling the pure digital mode of MMDVM and does not receive support from the official firmware, which is completely unnecessary.
A foreign HAM chose the finished product from this blog, deployed it on a mountain top 1000 meters high, using the jTA relay board + 2x GM338 + duplexer, covering a radius of 300 kilometers, and working stably 24/7.
Advantages:
The jTA series relay boards are redesigned by VR2VYE and BI7JTA from the public version, repeatedly tested, and strictly selected materials, making them easier to debug. No SDR or comprehensive testing instruments are needed to quickly complete deployment work (Note: Other sellers’ relay boards have extremely high debugging complexity, making it difficult for ordinary HAMs to complete alone). All units are tested before shipment in simplex/repeater mode, using equipment such as MOTO M120/GM300/GM338/CDM1250/GM3188, DMR/YSF/P25 modes, with a bit error rate <1% (depending on your radio).
Wiring Diagram Improved by This Blog:
This method does not require a TV stick or comprehensive testing instruments. First, look at the picture (updated 0806, corrected simplex yellow and white marks).
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Requirements: You need to have a basic understanding of the concepts of repeaters. If not, it’s okay; search Baidu for GM300 repeater setup. This blog simplifies the complex process, but it does not mean that you do not need to think or understand the basics. I have always been afraid of lazy people. If you have never played with MMDVM simplex hotspot boards, do not understand repeaters, and have not used one of the digital modes such as DMR, C4FM, P25, or DSTAR, then you need to study first. Read the pinned article “MMDVM Information Summary” on this blog! Basic questions have already been summarized in writing, so no need to ask again.
Preconditions:
1) External radios do not have frequency offsets and do not replace the original factory crystal oscillators (GM300/M120).
2) Read the “Verified Supported Radio List”.
3) Read “Introduction to Repeater Knowledge, New Uses for GM300, Teach You How to Use Two GM300s as Digital Repeater Stations”.
1 External Radio Hardware and Programming Configuration (External Radio Setting)
GM300/M120 Case:
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Duplexers: Two types, less than 25W and greater than 25W, need to be custom-made, can be purchased from this blog (see the Taobao link at the end of the article).
Write frequency, keep all parameters default, power set to low power 5W (writing frequency must be pure DOS, old computers like 586, COM port cannot be USB to TTL),
Receiver: Channel 1 RX/TX 434.755MHz, direct frequency, no sub-audio, no signaling;
Transmitter: Channel 2 RX/TX 439.755MHz, direct frequency, no sub-audio, no signaling;
GM338 MMDVM Case:
Hardware does not require any jumpers, tail insertion as shown.
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Write frequency (WinXP, Win7 are both fine, frequency writing software can be consulted from this blog, limited to repeater board users, time is limited)
Images are from the Internet, verified by BI7JTA on CDM1250, GM338 verified by BH1RQN, keep default configuration, but GM338 power defaults to 40 watts, which should be changed to low power, otherwise radiation is too large! Read the original text here.
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GM3188 MMDVM Case: Practical operation can be seen in Youku video podcast.
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2 P-Star Configuration (Raspberry Pi) and Terminal Radio Configuration (Simplex and Duplex Modes)
Purchase this blog’s Raspberry Pi or SDCard, the latest image is already built into the SDCard, configured as NOCALL, DMRid 4600000, just set the handheld radio to use, and you can also get configuration templates from this blog for direct import. For Modem Type selection, the jTA relay board supports GPIO and USB connections to the Raspberry Pi. If using USB, select STM32-DVM (USB), if using GPIO, see the diagram. For the Windows version of MMDVM software, you can also use USB directly, or use GPIO serial + USB to TTL adapter, see another article from this blog.
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Terminal Radio Settings, taking MD380G as an example
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If you need a template, leave a message on the forum to request it. The P25 mode template settings are similar to DMR. There is a template for XTS3000, and for YSF, you can directly set the frequency.
3 Debugging Steps
Taking DMR mode as an example, it is strongly recommended: Debug one by one through the simplex mode of the two repeater stations, then debug duplex mode, otherwise, it will be a shot in the dark!
Debugging RX (Terminal Radio –> Repeater Board)
1) According to the previous Pi-Star settings, open DMR mode. For first-time use, it is recommended to only open one mode. If you have not applied for a DMRid, you can use 4600000 instead. The DMR handheld radio’s DMRid must be registered with BM to connect to the server and obtain echoes.
2) The terminal radio’s individual call contact is 9990, CQ to listen for echoes. Or group call 4000 to hear the “disconnected prompt tone”.
3) Adjust RXLevel receiving gain/TXLevel transmitting gain on the repeater board.
4) When debugging repeater mode, if conditions permit, prepare two handheld radios, write in the repeater’s RX/TX frequencies, one transmits and one receives local difference transfer, listen for the effect. Note that the other cannot decode during individual calls; use group call 4000 or any string of numbers to do so, and more methods can be explored by yourself.
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Youku Video
http://list.youku.com/albumlist/show/id_51498838.html
RX reception:
http://player.youku.com/embed/XMzc0MjgwNTM2MA==?client_id=d0b1b77a17cded3b
TX transmission:
http://player.youku.com/embed/XMzc0MjgxMDc0MA==?client_id=d0b1b77a17cded3b
Potentiometer adjustment:
http://player.youku.com/embed/XMzc0MjgxNjg4OA==?client_id=d0b1b77a17cded3b
Debugging TX (Repeater –> Terminal Radio)
In fact, for the jTA series relay boards, keeping the TX potentiometer at the default value of 50% (adjustable range 0~10k ohms) can successfully decode, and there is no need to adjust Pi-Star RXLevel/TXLevel gain. This blog does not discuss more voltage and spectrum knowledge; professionals can refer to foreign blogs and YouTube videos.
If the terminal radio’s signal light is on but does not decode, and the repeater board receives the network signal, the repeater board’s PTT, etc., are on, prioritize checking whether the repeater radio’s configuration meets the previous descriptions. Some radios age significantly and can easily overheat or become offset in low temperatures. At this time, you can slightly adjust the repeater board’s TX potentiometer (the top one, adjustable range 0~10k ohms) until the terminal radio can decode clearly without any garbled sound. More advanced debugging requires professional instruments such as spectrum analyzers and oscilloscopes. However, an RTL-SDR (commonly known as a TV stick) can replace the spectrum analyzer. The jTA suggests that the significance of this kind of testing is not very large; the focus should be on checking radio frequency offsets and settings. Your board has passed my tests (GM300/M120/GM338) before reaching your hands.
A fairly perfect spectrum. Additionally, from my experience, boards made by several other sellers in China have very unstable spectra due to material selection issues, making it very difficult to decode perfectly. They also do not test before shipment, and if there are problems, they will make excuses. This is one of the reasons I recommend buying boards from this blog.
Soft Skills Mastery
This part originally belonged to the preconditions. Considering that HAMs who play with relay boards mostly have experience with hotspot boards, to avoid verbose explanations, I have placed it at the end of the article. You can also refer to another article from this blog, “MMDVM Tutorial Part Two, Assembling DMR/YSF/DSTAR/P25/NXDN Mini Repeaters with Duplex Boards”.
Because MMDVM includes hardware (i.e., hotspot boards) and software (Raspberry Pi system) parts. We call the hardware STM32 control system software firmware, and the Raspberry Pi software is called the system (OS). This operating system is called Debian, which can be understood as a kind of stuff (thing) like the Windows system. The PI-STAR system is a Debian system that packages a bunch of MMDVM programs.
1) Install the system. Although the finished product already comes with the system, it is still recommended to look at another article “Reinstalling the Pi-Star System Guide” for future upgrades and maintenance.
2) Apply for a DMRid. DMR and P25 modes, POCSAG require DMRid, D-STAR and YSF (C4FM) can directly use the call sign, but for interoperability, it is still recommended to look at “DMRid Registration”.
3) Register for the BM network (a website managing DMR services) https://brandmeister.network/?page=hotspot-edit&id=4600060 Click Register/Login in the upper right corner.
4) Set static groups. In DMR mode under duplex (repeater) mode, if you want to listen to two online call groups, you need to add time slot 1 (TS1) and time slot 2 (TS2) on the website; otherwise, you cannot achieve the PTT constant monitoring like the 46001 call group, which will drop after 15 minutes. Offline use or non-DMR modes can be ignored, and the address settings are the same as above (3).
Configuration Screens (Nextion, OLED)
Note: The MCU used by the relay board currently only supports USB to TTL connections for large screens. It is recommended to use a TTL adapter with the CP2102 chip, which can be purchased from this blog’s Taobao store.
When purchasing OLED, it is recommended to use 1.3 inches, which performs better than 0.96 inches. The wiring sequence is as shown VCC/GND/SCL/SDA. Regardless of whether it is a large screen or OLED, do not connect the positive and negative wires incorrectly! The screens do not have reverse connection protection.
Nextion wiring sequence:
USBtoTTL +5V –> Nextion +5V USBtoTTL RXD –> Nextion TX USBtoTTL TXD –> Nextion RX USBtoTTL GND –> Nextion GND
OLED: HS 3.3V –> OLED 3.3V HS GND –> GND HS SCL –> SCL HS SDA –> SDA
Setting Up Call Group Whitelist
The purpose is to add simple repeater management functions, valid only in DMR mode.
rpi-rwsudo nano /etc/mmdvmhost [DMR] Enable=1 Beacons=0 BeaconInterval=60 BeaconDuration=3 ColorCode=1 SelfOnly=0 EmbeddedLCOnly=0 DumpTAData=1 # Prefixes=234,235 # Slot1TGWhiteList= # Slot2TGWhiteList=
Firmware Upgrade
The relay board currently does not provide an online firmware flashing method. This blog will provide the upgrade method for jTA relay boards, which has three methods: 1) ST-LINK, this is the simplest method but requires purchasing an additional ST-LINK adapter, which is very cheap and essential for makers; 2) Raspberry Pi USB interface + bootloader jumper, see jTA’s GitHub repository; 3) Raspberry Pi GPIO + bootloader jumper, same as above. https://github.com/bi7jta/MMDVM-Install_RPT_N4IRS
Some suggestions: 1) Do not blindly buy clone versions for cheap without upgrade support; cheap means overdrawing the future; 2) Stability is sufficient; do not just pursue the latest version; upgrades require time preparation.
Common Problems (by encoding):
Usage Tips
User Cases
@BD7NJC Motorola M120, debugging method same as GM300, @BD7ILU GM300, cannot replace the original temperature-compensated TCXO, otherwise, the repeater board’s transmission (TX) will not be decoded by the terminal DMR radio. @BH3PXX GM300 DR-1X (Yaesu repeater) FT-7800 C4FM DMR @BH1RQN GM338, needs to enter Pi-Star expert mode to modify configuration TXInvert=0 http://pi-star/admin/expert/edit_mmdvmhost.php @DW4CHZ motorola maxtrac (Chinese translation called Mai Cang, a 90s machine, very rare in amateur bands) two radios are working good without any adjustment on board (no adjustment needed for hotspot board to work perfectly) @BI7JTA Motorola CDM1250 (American version GM338 6-key version): 1) Reprogram the radio configuration according to the CDM1250_GM338 configuration manual, 2) Enter Pi-Star expert mode to modify configuration TXInvert=0
Firmware Updates
Related Materials
Methods to adjust frequency offset for GM300
RTL-SDR analysis spectrum software to adjust TX transmission gain
User Sharing
@BG6BSP
Duplex mode ↑
Simplex mode ↑
POCSAG mode support (Tip: Clone boards do not support upgrades)
Other Radio Interface Definitions Reference (for record only)
FT-2720 /7800/8900/
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FT DR-1X
Duplexer Customization
High quality, delivery period of 2-3 days after payment, under 439.755MHz difference 5, under 439.500MHz difference 5 in stock, divided into two types: less than 25W and greater than 25W. Export to Europe, America, Southeast Asia, worth buying.
https://item.taobao.com/item.htm?id=571543707353
Purchase Method
https://item.taobao.com/item.htm?id=564478777221