LinHT-hw

Open-source, Linux-based, SDR handheld transceiver

What is LinHT?

LinHT is an open-source handheld software-defined radio (SDR) transceiver built around a modern Linux System-on-Module and a true IQ RF front-end.

It is the successor of the OpenHT project, with focus on:

• simpler and more maintainable hardware,
• no FPGA in the signal path,
• tight integration with Linux, GNU Radio, and modern SDR tooling,
• long-term openness and hackability.

LinHT is developed by members of the M17 community and is intended primarily for radio amateurs, SDR experimenters, and developers.

This repository contains the hardware design files for LinHT.

⚠️ Important
LinHT is not a consumer product yet. It is an experimental, community-driven open hardware project.

Key ideas behind LinHT

• True SDR: IQ baseband access, not FM-only
• Linux-first: no microcontroller firmware lock-in
• No FPGA: easier development, lower entry barrier
• Open everything: hardware, software, toolchains
• Hackable handheld: not just another black box walkie-talkie

Hardware overview

LinHT is built around a Linux SoM and a wideband IQ transceiver.

• System on Module: CompuLab MCM-iMX93
• RF front-end: Semtech SX1255

CPU

• Dual-core ARM Cortex-A55 @ 1.7 GHz
• ARM Cortex-M33 coprocessor @ 250 MHz
• Floating-Point Unit
• ARM Ethos-U65 microNPU (TensorFlow Lite support)

Memory

• 2 GB LPDDR4
• 32 GB eMMC

RF capabilities (revision B target)

Parameter	Value
Frequency range	UHF band (exact limits depend on PA/filter configuration)
Bandwidth	up to 500 kHz IQ
Architecture	Direct IQ (complex baseband)
TX power	up to ~5 W (revision B, internal PA)
RX features	Programmable attenuation, gain control
Modes	FM, SSB, M17, experimental digital modes

📌 UHF only!
VHF support is frequently requested, but is not planned for revision B. The current priority is stability, manufacturability, and software maturity.

Software overview

LinHT runs a custom Yocto-based Linux distribution designed for SDR and embedded radio use.

Supported development models

• C / C++
• Python
• GNU Radio flowgraphs
• SoapySDR
• Custom DSP pipelines

Standard Linux tools (gcc, gdb, strace, etc.) are available directly on the device.

Supported modes (current status)

• ✅ FM (TX/RX) with pre-/de-emphasis and CTCSS
• ✅ SSB (TX/RX)
• ✅ M17 (TX/RX)
• ✅ TETRA (RX only)
• 🧪 Experimental 64-QAM @ 2 Mbps
• ⏳ Planned / possible: FreeDV, APRS, packet radio, custom modulations

Hardware revisions

LinHT is developed iteratively. Each revision serves a specific purpose.

Revision	Status	Purpose
Rev. A	Completed	Early prototype, architecture validation
Rev. B	In progress	Feature-complete, manufacturing-ready design

Revision A

• Manufactured earlier in 2025
• 4 assembled prototype units
• Used to:
  • validate the Linux + SDR architecture,
  • bring up SX1255 under Linux,
  • start software and DSP development,
  • identify mechanical, RF, and power issues
• Revision A was never intended for production.

Revision B (current focus)

• Incorporates lessons learned from Rev. A
• Major improvements:
  • redesigned power supply
  • internal PA (~5 W)
  • improved RF path and attenuation for RX
  • cleaner layout and grounding
• Not yet released for manufacturing

📅 December 2025 status
Revision B is currently being finalized, manufactured, and tested. Please check this page later for updates.

Repository contents

This repository contains:

• KiCad 9.0 project files
• Schematics
• PCB layout
• Manufacturing outputs (generated automatically)

Gerbers, BOM, pick-and-place files, and schematics are:

• generated automatically via GitHub Actions
• published on GitHub Pages

Required hardware (donor radio)

LinHT is designed as a replacement mainboard for the Retevis C62 handheld radio. You will need:

• a Retevis C62 (donor device)
• its:
  • enclosure
  • display
  • keypad
  • battery
  • connectors

More details (Rev. A focused, older but useful): LinHT Open SDR Handheld For Radio Amateurs

Firmware images

Prebuilt Linux images for LinHT are available here: https://m17project.org/linht/

Documentation:

• https://wiki.m17foundation.org/index.php?title=LinHT_Image_Build

Yocto layers:

• meta-linht-hardware
• meta-linht-software
• meta-linht-sdr

Flashing the device

Flashing is done using NXP Universal Update Utility (uuu).

1. Boot LinHT into flash mode (hold the secondary side button while powering on)
2. Flash using:

uuu -v -b emmc_all imx-boot-mcm-imx93-sd.bin-flash_singleboot linht-image-mcm-imx93.rootfs.wic.zst

Tool download: mfgtools

To access LinHT’s USB network device on Windows, install the RNDIS driver: microsoft.com USB RNDIS Gadget

Documentation & Wiki

Primary documentation lives on the M17 Wiki:

• LinHT overview
• Image build instructions
• Image usage & manual

Contributing

LinHT is a community project and contributions are welcome. The best way to get involved is joining the M17 Discord, look for channel: #linht.

This is the preferred place to:

• discuss ideas,
• coordinate work,
• ask questions,
• avoid duplicated effort.

Other ways to contribute:

• Open issues in this repository (design notes, questions, suggestions)
• Help on the software side (especially welcome):
  • Yocto recipes
  • device tree improvements
  • CI / GitHub Actions
  • build automation
• Explore and extend LinHT-utils

If you’re an experienced embedded Linux or SDR developer, we would love your help.

FAQ – Frequently Asked Questions

❓ Where can I buy LinHT hardware?

You currently cannot buy LinHT as a product. To build LinHT, you need to:

• manufacture the PCB yourself (using provided Gerbers),
• source components,
• assemble the board,
• use a Retevis C62 handheld radio as a donor for:
  • enclosure,
  • display,
  • keypad,
  • battery,
  • connectors.

This may change in the future.

❓ Is LinHT suitable for everyday radio use?

Not yet. And maybe never in the "consumer radio" sense. LinHT is currently best suited for:

• developers,
• radio amateurs comfortable with Linux,
• SDR experimenters,
• people who enjoy building and debugging hardware.

You should not expect:

• plug-and-play user experience,
• polished UI,
• certification,
• warranty,
• commercial-grade RF compliance.

❓ Does LinHT support VHF?

No, not in revision B.

VHF support is a frequently requested feature, but it is not planned for revision B, adding another band significantly increases:

• RF complexity,
• filtering requirements,
• PCB area,
• development time.

Right now, the project is focused on:

• stabilizing the hardware,
• finishing revision B,
• improving software and DSP,
• validating the new power amplifier and RF chain.

VHF is not ruled out for future revisions, but it is not a current priority.

❓ Is LinHT certified / legal to transmit with?

LinHT itself is not certified. Responsibility lies with the builder and the operator. LinHT is intended primarily for:

• amateur radio use,
• experimental licenses,
• lab and research environments.

Always follow your local radio regulations.

❓ I want to help. Where do I start?

The best starting point is discussion. Join the M17 Discord, channel: #linht.

Good ways to contribute:

• software development (Yocto, drivers, tooling),
• testing and feedback,
• documentation,
• RF/DSP experiments,
• CI and automation improvements.

If you’re unsure where to help - just ask.

License

This project is licensed under: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International

You are free to:

• share
• adapt

Under the conditions:

• attribution
• non-commercial use
• share alike

Acknowledgements

LinHT is developed by the M17 community, with contributions from many individuals. Thanks to everyone testing prototypes, reviewing schematics, writing software, and sharing ideas.