Dilshan R Jayakody’s Web Log

BA1404 is quiet famous FM stereo transmitter IC manufactured by ROHM Semiconductor . This 18pin chip contains FM stereo multiplexer, 19 kHz pilot tone generator and RF output stage with the oscillator. The FM transmitter in this article is also based on BA1404 and 78L33 voltage regulator. The FM transmitter in this article is specifically designed to transmit audio signals generated by PC/Laptop sound cards. To archive this goal, this transmitter is designed to drive using a 5V DC power source. Except for Q1 (38 kHz crystal) and L2 (oscillator inductor), this transmitter uses commonly available electronic components. 38 kHz crystal is vital to generate 19 kHz pilot tone and this crystal is available to purchase in several web stores. For L2, wind 3 turns of 22 S.W.G enameled copper wire on 5mm bobbin with an adjustable ferrite core .  This variable inductor is used to select the output frequency of the transmitter. To archive good quality output and frequency stability ...

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 .

Steganography is a method of hiding information and one of the techniques is to hide an image inside a "cover image" by without distorting the supplied "cover image". ImageHide is command-line driven console application to perform this task and it is capable to hide/embed a colored or gray-scale image inside another color or gray-scale cover image and/or extract an embedded image from the supplied "cover image". This application is developed using FPC / Lazarus and it can execute on any FPC supported operating system which including Linux, Windows, Mac OS, etc. ImageHide is an open source project and its source code is available at https://github.com/dilshan/image-hide under the terms of GNU General Public License version 3.0 . Compiled binaries of ImageHide are also available for both Linux and Windows operating systems. As an input, this application accepts bitmap, PNG or JPEG image formats and it can export the processed image as bitmap or PNG ...

Audio Signal Generator (or AF Signal Generator) is often used in RF and AF base designing and experiments. In this article we introduce less complex AF signal generator based on commonly available electronic components. The heart of this AF signal generator is Intersil ICL8038 precision waveform generator/voltage controlled oscillator IC. ICL8038 is a function generator capable of producing sine, square and sawtooth waveforms at same time. In this project we combine ICL8038 with inverting and non-inverting amplifiers to get above mentioned 3 waveforms with 0° and 180° phase differences at the same time. Those inverting and non-inverting outputs help to use this AF signal generator with balanced audio systems. Final version of AF signal generator. The given schematic and PCB design of this AF signal generator contains ICL8038 waveform generator, inverting and non-inverting amplifier stage, output buffer and 12V regulated power supply. All the above mentioned modules are integrat...

This is simple radio receiver project which is capable to receive aviation radio voice signals which are transmit between 118MHz to 138MHz in AM (A3E). We got initial idea of this project by reading Sverre Holm’s (LA3ZA) article about " cheap VHF receiver project ". Like LA3ZA’s original article this project is also based on Samsung’s KA22429 FM radio receiver IC. KA22429 is low voltage FM radio receiver system developed by Samsung for portable radio receivers and as described by Holm’s it can push into VHF region by changing few values in its original circuit. In this project we redesign the schematic and PCB with some of those changes and now it can directly tune into aviation band with minimum number of adjustments. The dimension of PCB of this receiver is 70mm × 45mm and all the components except KA22429 are standard through-hole type. KA22429 testing setup with 5V PSU and AF power amplifier. For the optimal results we recommended to use high gain audio power ...

This is modified version of commonly available automatic car battery charger system. I obtain original layout of this charger from one of the commercially available Chinese car battery charger and modified some of the sections of original schematic to improve the performance and stability of the system. This charger is mainly based on LM311 comparator and 2 ×12V 4A transformer. Final view of automatic car battery charger All the components of this car battery charger are commonly available in the market. Ammeter in this system must be withstand for minimum of 8A current. Low cost ammeter can also be used with suitable shunt. For the relay it is highly advisable to use some high quality unit. During our prototyping we mainly use 12V Omron and Panasonic realys with this system. At the test stages we observe that some of the cheap relays may start to oscillate heavily with this system. Automatic car battery charger finished prototype Under normal conditions TIP142 and 7805...

This is 5 element Yagi-Uda antenna for 144MHz amateur radio transmissions and receiving. This antenna is design using commonly available TV antenna parts. The CAD drawing of this antenna is available to download in my QSL.net pages and all the measurements in that diagram are in mm (millimeters). The total boom length of this antenna is around 1500mm and maximum span is 1016.10mm. 3D visualization of 5 element Yagi antenna After the construction I test this antenna on 145.625MHz and got SWR of 1:1.3 with quiet lengthy, standard 50Ω RG-58 cable. With high quality shorter cable I achieve SWR of 1:1.1 - 1:1.2.