QRP Labs QDX Digital Transceiver

Introduction

The QDX is a high-performance, five-band 5W Digital modes transceiver. It features a built-in USB sound card and CAT control, offering an exceptional ratio of performance to price. This manual provides detailed instructions for assembly, an in-depth look at the design, and performance measurements.

Key features include:

• Five-band operation (80-10m) with 5W output from a 9-10V supply.
• Clean single signal output with zero residual carrier and zero unwanted sideband.
• Solid-state PIN-diode switched Low Pass Filters and Band Pass Filters.
• High-performance embedded-SDR SSB receiver with a 112dB 24-bit stereo ADC chip.
• Built-in USB sound card supporting 48ksps 24-bit stereo audio.
• USB Virtual COM port for CAT control.
• High-precision Si5351A synthesized local oscillator with better than 0.001Hz resolution.
• 25MHz TCXO reference as standard.
• Built-in signal generator and configuration/analysis tools.
• Lifetime free firmware upgrades via QRP Labs Firmware Update (QFU) bootloader.
• All SMD components are pre-installed; only through-hole components require soldering.
• Low receive current (150mA) and transmit current (1.0-1.1A at 9V, 5W output).
• Minimal connectors: USB, Power, PTT, and RF.
• Optional smart aluminum extruded enclosure available.

No external test equipment is required for building, aligning, or operating the QDX. This manual guides you through the assembly process step-by-step. For operating the QDX with software like WSJT-X, please refer to the separate operating manual.

IMPORTANT: Carefully read the basic assembly and use instructions before applying power to the board.

Assembly Guidelines

Assembly is straightforward, with most SMD components pre-installed. It is recommended to work in a well-lit area with minimal distractions. Be mindful of static discharge and take appropriate precautions.

• Follow instructions carefully; do not attempt assembly without the manual.
• A jeweler's loupe and a fine-tipped soldering iron are recommended for inspecting joints and soldering.
• Triple-check component values and locations before soldering.
• Use a good quality soldering iron and solder for best results.
• Refer to the PCB layout and track diagrams provided in the manual.

Design Overview

The QDX incorporates several advanced design elements:

• Synthesized local oscillator for precise frequency control.
• Solid-state transmit/receive switching for efficient operation.
• Double-balanced Quadrature Sampling Detector for high-quality signal reception.
• Low noise balanced differential pre-amplifiers.
• Analog to Digital Converter for SDR functionality.
• Embedded Software Defined Radio architecture.
• Embedded 24-bit 48ksps stereo USB Sound card.
• CAT control serial interface for remote operation.
• Class-D Push-pull Power amplifier for efficient output.
• Switched output Low Pass Filters for clean transmission.
• Configurable PTT output.
• Voltage regulation and supply decoupling for stable operation.

Performance

The manual details performance measurements, including receive and transmit current consumption, power output versus supply voltage, output harmonic content, and unwanted sideband suppression. These measurements are crucial for understanding the transceiver's capabilities.

Resources

Additional resources, including the document revision history, are available within the manual to assist users.