ADX - DIGITAL MODE TRX

ADX – Digital Mode HF QRP Transceiver Platform

The ADX Digital Mode TRX is a compact, efficient, and highly accessible HF QRP transceiver platform designed specifically for digital amateur radio operation. Developed within the WB2CBA ADX ecosystem, this design focuses on simplicity, affordability, and reliable performance for modern computer-assisted radio communication.

The ADX system is optimized for digital modes such as FT8, FT4, JS8Call, and WSPR, where signal processing is handled primarily by an external computer. This allows the hardware design to remain simple while maintaining strong real-world performance across HF bands.

At its core, the ADX uses a microcontroller-based control system paired with a Si5351 frequency synthesizer, providing stable and accurate RF signal generation. The receiver architecture is based on a direct conversion / simple superhet hybrid approach, enabling efficient signal handling with minimal component complexity.

The transmitter section typically uses a low-power MOSFET RF stage (commonly BS170 or equivalent depending on variant), delivering efficient QRP output suitable for digital duty-cycle operation.

The system is designed around a modular band-pass filter architecture, allowing users to operate across multiple HF bands by swapping filter modules. This makes the ADX highly flexible while keeping the main RF design simple and cost-effective.

Computer integration is a key feature of the ADX platform. The radio connects via USB and operates using CAT control (Kenwood TS-2000 emulation style) along with standard audio interface routing. This allows seamless operation with software such as WSJT-X, enabling full digital mode functionality with minimal setup.

The ADX philosophy is based on ease of construction, low cost, and global accessibility, making it one of the most widely adopted open-source digital transceiver platforms in the amateur radio community.

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Key Features

• Digital mode optimized HF QRP transceiver
• Designed for FT8, FT4, JS8Call, WSPR operation
• Si5351 frequency synthesis system
• Microcontroller-based control (ATmega328 family)
• Low power MOSFET RF output stage (QRP operation)
• Modular plug-in band-pass filter system
• USB CAT control (Kenwood TS-2000 style emulation)
• PC soundcard-based audio interface
• Multi-band HF capability via filter swapping
• Open-source inspired WB2CBA ADX architecture

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System Overview

The ADX operates as a computer-assisted HF transceiver, where most modulation, demodulation, and signal decoding is handled by the PC. The hardware provides:

• RF generation and filtering
• Transmit power amplification
• Receive signal conversion
• Band selection via filter modules

This separation of roles allows the system to remain simple, low cost, and highly reliable for long-duration digital operation.

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Applications

• Amateur radio HF digital modes
• FT8 / FT4 / JS8Call / WSPR operation
• QRP experimental transceivers
• SDR-style PC-controlled radio systems
• Educational RF and electronics projects
• Multi-band portable HF setups

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What’s Included

• ADX Digital Mode TRX PCB (variant dependent)
• Si5351 frequency generator interface
• RF output stage PCB design (MOSFET-based)
• Band-pass filter interface support
• Build documentation / wiring guidance