Dilshan R Jayakody’s Web Log

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...

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...

This project is about a wireless musical call bell, which I designed to meet some of my friend's requirements. This circuit design uses only the 4000 series CMOS logical ICs, NE555 , UM66 , and TDA7233 audio amplifier IC. For the remote control, we use a 433MHz 4-channel remote control module . This circuit is designed to work continuously with a low-power external 5V power supply. Prototype version of wireless call bell. The PCB in this call bell is designed as a single-sided PCB. The dimension of the PCB is 82mm × 50mm.  All the components in this circuit are commonly available through-hole-type components. The whole assembly process of this musical call bell is shown in the video attached to this document. The RF remote control module we use in this project consists of a remote control decoder and encoding IC. In our version, the transmitter (key fob) has a PT2262 encoder, and the receiver has a PT2272 decoder IC. In the prototype build, the receiver and transmitter are confi...

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle.  In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

This is simple Colpitts oscillator to test commonly available passive crystals which range between 2MHz to 27MHz. This unit must connect to an oscilloscope and/or frequency counter to get the frequency of the crystal. This circuit is designed to work around 9V to 12V DC power source. Both 2SC930 transistors can replace with any high-speed NPN transistor such as 2SC829, 2SC933, etc. Testing 5030kHz FT-243 crystal using a prototype version of crystal tester. In our lab, we use Manhattan-style layout to prototype this crystal tester and it produces highly accurate results with an above-specified frequency range. According to our observations, after 27MHz, the amplitude of the waveform starts to decrease steeply. Schematic and Stripboard wiring layout for this crystal tester is available to download in here .

This is a quick post about 100W RF dummy load which we build to use with HF and VHF transmitters and transceivers. This dummy load uses two non-inductive 100Ω 50W thick film power resistors manufactured by Vishay Sfernice and both these resisters are connected in parallel to achieve 50Ω impedance. The final version of 100W RF dummy load. Outer-casing (which also act as a heatsink) of dummy load is constructed using four bonded fin 50mm × 115mm × 20mm heatsinks. During our testing, we got flat 1:1.2 SWR with this dummy load. Internal view of 100W RF dummy load. Above mentioned 100Ω 50W power resistors are obtained through Farnell element14 .

After the 2 weeks of continues development we finally design suitable RC remote control system for cars. This RC system has, Battery eliminator circuit (BEC) Control System 433MHz transmitter and receiver module Motor driver and servo controller In this design both transmitter and receiver modules are based on seeed studio’s 433MHz RF link kit and control systems are based on microchip’s PIC16F84A MCU. At the design time we test this circuit with Futaba, Airtronics, JR-Radios, HiTec and "Mystery" (available in eBay) micro-servo units. This circuit may support standard electric motors (brushed DC motors) and during the testing stages we drive RC helicopter motors and RC airplane motors successfully with this system. To drive this circuit we use 7.2V 500mAh Li-Po batter pack. During the circuit assembling and testing, make sure to take necessary actions (e.g: shielding) to prevent/minimize the EM interferences which was generated by the motors. Most of the time t...