Dilshan R Jayakody’s Web Log

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 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...

Recently I got an interest to experiment with NOAA weather satellite reception techniques. As a first thing, I did search on the internet for a suitable antenna for NOAA satellite frequencies (137.100 MHz - 137.9125 MHz). After examining a couple of designs, I decided to build a Turnstile antenna which is designed by Ivo Brugnera I6IBE . Due to the COVID19 lock-down, I build this antenna using parts that are already available in my inventory. Originally, I build this antenna on a wood-stick, and later I changed it to a stable setup as shown below. Assembled antenna for 137 MHz NOAA weather satellite receptions. Following materials and components are used for the above construction: - Two 8cm × 8cm × 6cm waterproof ABS project box. - 54cm long, ⌀ 21mm PVC tube, which is reinforced by inserting water resistivity wood stick. - 8mm thread roads. - M8 nuts and M8 flat washers. - 50Ω and 75Ω coaxial cables. - PL259 male and female connectors. Before constructing this ant...

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.

This DIY project happens because of some request of my family members. The ultimate goal of this project is building analog TV antenna to receive UHF and VHF channels with minimum distortion, noise, materials and time. All the building materials of this antenna are available in general electronic shops and hardware stores. I got excellent results from this antenna in my home town: Maharagama ( Colombo , Sri Lanka) with all the locally available VHF and UHF channels. Technical drawing of this antenna is available to download in here .

In this project we design 8 feet C band satellite dish antenna and some of its specifications are listed in below, Diameter of the reflector : 248.0cm F/D ratio : 0.391 Focal length : 91.5cm Calculated gain (Aprox.) : 40.23 dB Materials used for reflector : Aluminum sheets and Aluminum nets Number of panels (in reflector) : 4 units Materials used for Mounting mechanism : Steel Weight (Aprox.) : 40 - 45 kg (without antenna positioning system) LNBF : Generic dual twin C band LNBF Antenna positioning system : Using D.C motorized actuator