Overview

Lars Petersen (OZ1BXM) documented his build of the 7-band ADX-S transceiver kit from CRKits in a detailed blog post. The guide covers assembly challenges, technical details, and practical operating tips for ham radio operators looking to build their own digital mode QRP station.

Build Details

Kit Source: 7-band kit from crkits.com
Physical Design: Three 9.7cm x 9.7cm circuit boards sandwiched together using threaded spacers (an innovative enclosure solution)
Complexity: Medium difficulty — closely-spaced solder pads require care, but all components are through-hole
Output Power: 2-3 watts RF depending on band selection

Key Lessons Learned

Critical: Swapping inductor positions L1 and L3 on low-pass filter boards eliminates transmit output entirely — double-check placement before soldering
Band-specific filter modules are interchangeable, allowing multi-band operation by swapping modules
The Arduino Nano and Si5351 modules come pre-assembled with SMD components

Technical Architecture

Receiver: CD2003 IC with 455 kHz superheterodyne IF and ceramic filtering
Transmitter: Direct frequency generation via Si5351 feeding parallel MOSFET amplification
Control: Arduino Nano microcontroller

Software Options

Primary: WSJT-X (free, cross-platform) for FT8, FT4, and WSPR
Mobile Alternative: FT8CN Android app for field operation without a laptop

Supported Bands

7-band configuration covering 40m, 30m, 20m, 17m, 15m, 12m, and 10m.

OZ1BXM ADX-S Build Guide — 7-Band Arduino Digimode Transceiver