Dilshan R Jayakody’s Web Log

Ecowitt2APRS is a new open-source Linux service that I have been working on for the past few weeks. This project is designed to seamlessly integrate weather data from Ecowitt compatible professional weather stations into the global Automatic Packet Reporting System Internet Service (APRS-IS) network, transmitting this information in the standardized format of APRS weather packets. APRS, an amateur radio-based system, facilitates real-time tactical digital communications, covering applications such as GPS position reporting and the dissemination of meteorological data. Ecowitt2APRS addresses a specific need within this ecosystem: providing a lightweight and efficient method for weather stations to contribute to this data stream. Live data view from my Ecowitt weather station on aprs.to. The Ecowitt2APRS service is developed as a minimalist daemon for Linux environments. It ingests live weather data from Ecowitt compatible stations, converts it into the required APRS weather pac...

This blog post discusses the engineering design, construction, and performance evaluation of a 4-element Yagi-Uda antenna specifically optimized for the 2-meter amateur radio band, focusing on the frequency range of 144MHz to 145.5MHz. The project was initiated to establish strong and reliable communication with distant VHF repeaters of the RSSL ( Radio Society of Sri Lanka ), which are located approximately 58km and 96km from my location. The finished antenna, oriented towards the Yatiyantota repeater. The primary objective was to develop a high-gain, directional antenna with a superior front-to-back ratio. This directionality is essential for maximizing signal capture from the desired repeater while minimizing interference and noise from unwanted directions, ultimately improving the SNR and the quality of the communication link. VHF communication at these distances typically relies on line-of-sight propagation, making antenna gain a critical factor in overcoming path loss and ...

This project is about MC3362 and ADF4351 based modularized, 2-meter narrow band FM receiver. In this design, the receiver splits into three modules as RF preamplifier, MC3362 tuner, and ADF4351 oscillator. The RF preamplifier builts around BF900 dual-gate MOSFET. The tuner stage builts using the popular MC3362 , low power narrowband FM receiver IC. For the oscillator, we use the ADF4351 DDS RF signal generator module. The core component of this receiver is MC3362 IC. This IC was designed by Motorola and is no longer in production, but this IC is still available to purchase in many online stores . The chip we used in this receiver was purchased from a local electronic component store for LKR 75 (USD 0.2). The RF preamplifier used in this receiver extracts from the N.Ganesan's (VU3GEK) LRR200, 2-meter band FM receiver project . Prototype version of the RF preamplifier. In this prototype, the above preamplifier was built as a module using a Manhattan construction technique. Th...

The 1750Hz tone bursts are often used to trigger repeaters. There are several methods to build 1750Hz tone generators which including TC5082 divider , using MCUs, etc. In this post, I present another 1750Hz tone generator which I built using 74HC4060 high-speed 14-stage binary ripple counter and 7.168MHz crystal. In this design, 74HC4060 is used to drive the crystal and divide its output by 4096. By using 7.168MHz crystal, this circuit produces 1750.0Hz square wave output with a 50% duty cycle. A prototype version of the 1750Hz tone generator. This circuit is extremely simple to build, and I construct my prototype using a breadboard. I tested this generator by connecting its output to my Baofeng UV-5R handheld transceiver and it gives an excellent result. The key motivation to build this generator using 74HC4060 is, because of its common availability. Most of the tone generators which I found on the internet are built using MCUs or by using rare ICs, because of that rea...

13.8V power supplies are commonly used in amateur radio experiments. Most of the portable amateur radio transceivers are designed to work with a 13.8V power source. We mainly build this power supply unit to power some of our amateur radio circuits and modules. This design is based on the popular LM338 5A voltage regulator. We choose this regulator because of to it’s higher current rating, short-circuit protection feature and higher availability. The prototype version of 13.8V - 5A power supply unit. Apart from that, we include MC3423 based crowbar sensing circuit to preventing an over-voltage condition of a power supply unit. We design this circuit by using commonly available 18V×2 (5A) + 12V (1A) transformer. This transformer is available in the market because it’s commonly used with some AF power amplifier systems/kits. We use its 12V terminal to drive 120mm - 12V cooling fan.

Morse View is an open source software project to convert audible Morse codes to text messages. This application is capable to convert Morse codes from wave files or from the audio line/microphone inputs. Conversion from Morse code to text can perform based on amplitude and frequency decomposition of the input audio stream. Morse View decoding 25 WPM Morse code wave file We extensively test this application using Morse code files available at ARRL - W1AW code practice page . During the testing we may be able to use this application to decode 5WPM – 40WPM Morse code inputs. As per our test result, after 25WPM, accuracy of the decoder is heavily depends on the quality of the sound card / audio capture device (ADC) and with the system configuration. We test this system with few audio adapters, and out of those adapters both Creative Sound Blaster X-Fi and VIA VT1723 generate more accurate results, especially on 25WPM – 40WPM range. We test this software with different noise c...