USDX
A simple, experimental, and low-cost software-defined SSB and CW transceiver for QRP HF radio communications.
Overview
uSDX is an open-source, experimental software-defined radio (SDR) transceiver designed for low-power (QRP) single sideband (SSB) and continuous wave (CW) HF communications. It operates across multiple amateur radio bands from 160m to 10m and supports all common modes including USB, LSB, CW, AM, and FM. The transceiver leverages a highly power-efficient Class-E amplifier design combined with a software-driven SSB transmit stage implemented on an ATMEGA328P microcontroller. This approach minimizes hardware complexity and cost while maintaining reasonable performance for practical QSOs, including contest conditions.
The uSDX transceiver features a fully digital SDR receiver with software-based 90-degree phase shifting, DSP filtering, automatic gain control (AGC), noise reduction, and multiple analog front-end attenuators to optimize dynamic range. The transmit stage reconstructs the SSB signal by controlling the SI5351 PLL phase and power amplifier envelope via PWM, enabling a compact, low-heat, and efficient design without bulky linear amplifiers. Firmware is open source and built with the Arduino IDE, allowing users to customize and extend functionality. The device supports VOX for fast RX/TX switching and CAT control for remote operation.
What sets uSDX apart is its minimalist hardware design—only four ICs plus a microcontroller and a few passives—combined with advanced software DSP techniques to achieve sideband suppression better than -45dBc and output power around 5W PEP from a 13.8V supply. Its continuous tuning capability across HF bands and support for digital modes like FT8 via VOX make it versatile for amateur radio enthusiasts who want a low-cost, DIY SDR transceiver. The project is actively maintained with a community forum for support and collaboration. Getting started involves assembling the hardware or purchasing kits, then uploading the open-source firmware via ISP or Arduino IDE.
The Problem
Traditional SSB transceivers often require complex, power-inefficient linear amplifiers with bulky heat sinks, making them expensive and difficult to build for QRP operators. Analog designs also demand precise I/Q alignment and lack flexible DSP features, limiting performance and adaptability.
The Solution
Key Features
Continuous tuning across 160m-10m bands
Supports USB, LSB, CW, AM, and FM modes with 2400Hz bandwidth.
DSP filters and noise reduction
Includes adjustable passbands, AGC, noise reduction, and multiple attenuators for optimal reception.
Software-based full Break-In VOX
Enables fast RX/TX switching for voice and digital modes without external PTT.
Key Strengths
How Developers Use USDX
QRP HF SSB Voice Communications
Amateur radio operators use uSDX to make low-power voice contacts across HF bands with a compact, efficient transceiver.
Digital Mode Operation (FT8, JS8, FT4)
Combined with a PC and VOX mode, uSDX supports digital modes by routing audio through sound cards without additional hardware.
DIY SDR Experimentation and Development
Hobbyists and developers modify and extend the open-source firmware and hardware to explore SDR techniques and custom features.
Works Well WithKava
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Pricing
Open Source | |
|---|---|
| Price (Monthly) | Free |
| Price (Annual) | Free |
| Messaging | N/A |
| Support | Community support via GitHub and uSDX Forum |
| Analytics |
Resources
The uSDX project provides extensive open-source resources including firmware source code, schematics, block diagrams, and detailed operating instructions. The GitHub repository hosts the latest firmware releases and documentation. An active community forum supports collaboration and troubleshooting.