This blog post details the creation of an open-source DMR (Digital Mobile Radio) transceiver using software-defined radio (SDR) with GNU Radio and the Codec2 vocoder. The author outlines the process of building the system, highlighting the integration of different components like the MMDVM modem, a modified version of the AMBE codec (Codec2), and GNU Radio for signal processing. The implementation allows for real-time DMR communication, demonstrating the feasibility of building a completely open-source DMR system. This project offers an alternative to proprietary DMR solutions and opens possibilities for experimentation and development within the amateur radio community.
The author investigates strange, rhythmic noises emanating from a US Robotics Courier V.Everything 1670 external modem. Initially suspecting a failing capacitor, they systematically eliminated various hardware components as the source, including the power supply, cable, and phone line. Ultimately, the culprit turned out to be a loose metal plate inside the modem vibrating against the plastic casing at specific frequencies, likely due to the interplay of electrical signals and component vibrations within the device. Tightening the screws securing the plate resolved the issue. The author reflects on the challenge of diagnosing such elusive hardware problems and the satisfaction of finally pinning down the root cause.
HN commenters discuss the nostalgic appeal of the 1670 modem's sounds, with some sharing memories of troubleshooting connection problems based on the audio cues. Several delve into the technical aspects, explaining the meaning of the different handshake sounds, the negotiation process between modems, and the reasons behind the specific frequencies used. The infamous "Concord jet taking off" sound is mentioned, along with explanations for its occurrence. A few lament the loss of this auditory experience in the age of silent, high-speed internet, while others express relief at its demise. There's also discussion of specific modem brands and their characteristic sound profiles, alongside some speculation about the article author's connection issues.
Summary of Comments ( 5 )
https://news.ycombinator.com/item?id=43735945
Hacker News users expressed excitement about the open-source DMR implementation, praising its potential to democratize radio technology and make it more accessible for experimentation and development. Some questioned the legality of using DMR without a license and the potential for misuse, while others highlighted the project's educational value for understanding digital radio protocols. Several comments focused on the technical aspects, discussing the challenges of implementing DMR, the performance of Codec2, and the potential for integrating the project with existing hardware like the HackRF. A few users also expressed interest in similar open-source implementations for other digital radio protocols like P25 and NXDN.
The Hacker News post titled "Open Source DMR Modem Implementation in SDR with GNU Radio and Codec2" has generated a moderate amount of discussion, with several commenters expressing interest and raising pertinent questions.
One of the most compelling threads involves the licensing of the Codec2 voice codec used in the project. A commenter highlights potential GPL licensing implications when combining Codec2 with GNU Radio, which is also GPL licensed. This sparks a discussion about the nuances of GPL licensing and whether static or dynamic linking of Codec2 affects the overall licensing requirements of the project. This thread is important as it raises practical concerns for anyone looking to build upon or modify this open-source project.
Another commenter questions the choice of DMR, pointing out that it is a proprietary standard controlled by Motorola. They express a preference for open standards and question the long-term viability of building upon a closed standard. This raises a valid point about the potential limitations and risks associated with relying on proprietary technology.
Several commenters delve into technical details, discussing the challenges of implementing DMR, including the complexities of its two-slot TDMA structure. They also discuss potential applications of the project, including using it for emergency communications and amateur radio.
Some users also share their experiences with DMR and other digital voice modes, providing valuable context and insights into the practical use cases of such technologies. They discuss the tradeoffs between voice quality, bandwidth efficiency, and complexity.
Finally, a few commenters express excitement about the project and commend the author for their work, recognizing the potential of open-source DMR implementations to foster innovation and experimentation in the field of digital radio.
Overall, the comments section provides a valuable mix of technical discussion, licensing concerns, and practical considerations related to the open-source DMR modem implementation. It highlights both the promise and the challenges of working with open-source and proprietary technologies in the realm of digital radio.