Dilshan R Jayakody’s Web Log

I found the ZZRX-40 receiver while going through some old issues of QEX magazine . Designed by Craig Johnson (AA0ZZ) , this is a very simple and easy-to-build 40m direct conversion receiver. Even though it is a simple circuit, it performs quite well for its size. Prototype version of extended ZZRX-40 receiver. For this project, I decided to make my own PCB design because I wanted to use components that I could easily find in our local shops. Since I couldn't find any PCB files online, I drew the schematic in KiCad and designed a custom board. If you are interested in building this, I have shared the Gerber files and KiCad project files here: https://github.com/dilshan/zzrx40-clone . Antenna connector and external VFO headers (JP101 and JP102). The heart of this receiver is the popular NE602 (or SA602 ) mixer chip. This single chip handles both the local oscillator and the product detector, which makes the whole circuit very compact. Although it is designed for the 40-mete...

I recently received a DIY two-tube FM receiver kit from one of my Chinese component suppliers for review. The circuit is elegantly simple, designed around a 1A2 heptode and a 2P2 pentode . The kit includes all the necessary components for the build, featuring a single-sided FR4 PCB with dimensions of 100mm × 100mm. Assembled PCB with tubes. The primary hurdle when starting this project was the complete lack of proper assembly instructions. To assist others, this article documents the exact steps I took to assemble and test the receiver. I have also reverse-engineered the schematic based on the PCB layout; a high-resolution PDF version is available for download here . Top view of the PCB. Bottom view of the PCB. The radio is designed around two main stages to handle frequency conversion and audio amplification: The 1A2 heptode - functions as a super-regenerative detector. The 2P2 pentode acts as the audio power amplifier, which receives the demodulated signal and drives the ...

For an amateur radio operator, having a real-time dashboard is essential for monitoring band conditions and identifying DX opportunities. While several solutions exist, I recently completed a project centered on OpenHamClock , an open-source, web-based successor to Elwood Downey’s (WB0OEW) original HamClock . My goal was to move beyond simply opening a browser tab and instead create a dedicated, always-on kiosk for my workshop/shack. This setup allows me to monitor live DX cluster spots, PSKReporter reception, and satellite X-ray flux in real-time, helping me decide exactly when to jump into a radio session. Prototype build of OpenHamClock kiosk. The heart of this project is a two-component system: a centralized server and a remote kiosk unit. For the server, I utilized a PC equipped with an AMD Ryzen 7 series CPU and 32GB of RAM. While this machine hosts multiple other services, it serves as the perfect, reliable host for the OpenHamClock backend. The installation process is...

This project began with a simple idea: to build a fully functional digital desk clock using only classic CMOS logic ICs that are still readily available in local electronics markets. No microcontrollers, no firmware, no programmable logic - just counters, flip-flops, logic gates, and seven-segment decoders doing exactly what they were designed to do. The result is a 24-hour digital clock powered from a 5V, 1A supply, drawing roughly 200mA, and assembled entirely by hand on a perfboard using point-to-point wiring. Fully assembled CMOS desk clock. At the heart of the clock is a traditional timebase derived from a 32.768kHz crystal oscillator. This frequency is widely used in timekeeping because it can be divided cleanly to exactly 1Hz. A CMOS frequency divider, such as the CD4060 and CD4013 , performs this task, producing a precise one-second pulse that serves as the master clock for the entire system. From this point onward, time is counted purely in hardware, one pulse at a time...

The BG7TBL FA-5 frequency counter has become recognized as an excellent choice for experimenters and radio enthusiasts, offering high-spec performance comparable to branded units. But it remains remarkably accessible due to its low cost.  FA-5 Frequency counter. The FA-5 has powerful hardware. However, most existing control applications lack a good user experience. Many of them rely on scripting languages, such as Python, while others utilise simple command-line interfaces . These limitations inspired us to create FA-5 VizControl . This native application provides a comprehensive, intuitive, and portable desktop experience for managing the FA-5 . We developed FA-5 VizControl using Lazarus and the FPC ( Free Pascal Compiler ). This choice ensures maximum compatibility and portability. The application functions as a standalone, portable executable on both Linux and Windows operating systems. There is no need for complex installation routines. Users simply download and launch...

This is a simple surge arrester array that I made in my free time. Built using readily available components, the array provides effective shielding against lightning-induced surges and static discharges that can damage sensitive transmitting and receiving systems. The primary goal of this project was to create a robust, low-loss surge protection unit that can handle multiple RF lines simultaneously. By integrating gas-discharge based lightning arresters with a solid grounding infrastructure, the array ensures that transient over-voltages are safely diverted to ground without affecting normal signal transmission.  Installed surge arrester array. The core of this project relies on a few key components: At the heart of the design are eight BL-2000 Lightning Arresters , each incorporating a GDT ( Gas Discharge Tube ). These units are designed to conduct high-voltage transients from the coaxial line directly to ground within microseconds of a surge event. The BL-2000 series is a...

The Arduino Mini Amplifier is a compact audio system that merges vintage analog and modern digital components. It combines a Philips TDA8425 audio processor and an Arduino Nano , supporting Bluetooth and line-in audio, spectrum analysis, stereo modes, and software-controlled tone adjustment. Finished prototype of the Arduino Mini Amplifier. The Arduino Mini Amplifier is organized into six major subsystems: the audio processor, spectrum analyzer, Bluetooth source, power amplifier, control interface, and power management unit. This modular setup allows each part to operate with minimal interference from the others, making designing and PCB routing easier. The system uses separate paths for analog and digital ground signals (these are called GNDA for analog ground and GNDD for digital ground). Their connections are limited to specific points, which helps prevent unwanted electrical noise from the MCU from reaching the analog audio circuits. The audio section is centered on the T...