Homepage of 4S6DRJ

Hello, welcome to the ham radio page of 4S6DRJ. I own this callsign and I'm Dilshan R Jayakody. My QTH is Maharagama Sri Lanka. By profession I'm a software engineer and mainly work on embedded systems, operating systems and video gaming areas.
I was interested in electronics and spend most of my leisure time by designing and constructing electronic circuits. Most my electronic and related designs and constructions are available at my blog and flickr pages. I get into amateur radio at 2013 with novices class license and my initial call sign is 4S5DRJ. At 2015 February I upgrade my license to general class and my current call sign is 4S6DRJ.
Other than software and electronics I'm interested about Astronomy and Meccano (/Erector) modelling. 
I'm still updating this page and in near future I plan to fill this page with more information. If you wants to know more about me please check my homepage and blog. All my contact details are available at my homepage.

Amateur radio and communication related projects and articles

137 MHz NOAA Antenna  

NOAA weather satellite reception

This article explains my setup to receive NOAA weather satellite images using homemade turnstile antenna, RTL SDR, and PC. Using this setup, I got weather satellite images from all the active NOAA satellites on 137 MHz.

The antenna which I use for this project is base on the design done by Ivo Brugnera I6IBE.

USB Morse Keyer  

USB Morse Keyer

USB Morse Keyer is PIC16F886 based automatic Morse code keyer with USB and Morse key interfaces.

Using this automatic keyer Amateur radio operator can send Morse code messages either using PC or conventional Morse key. This unit is designed to work with the majority of transmitting devices, and also it includes options to extend its feature with minimum modifications.

Eddystone EC10 Receriver Repair  

Eddystone EC10 communication receiver restoration and PSU add-in

This page contains details of Eddystone EC10 communication receiver repairing process and suitable AC power supply unit.


Trio JR-310 and TX-310 restoration project

This article contains logs related to Trio TX-310 and JR-310 HF transmitter and receiver restorations. Both TX-310 and JR-310 are vacuum tube and transistor base units and manufactured around 1960’s by Trio Corporation - Japan (now Kenwood).

144MHz Yagi Antenna  

Homebrew 5 element Yagi antenna for 144MHz

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 above link 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.

After the construction I test this antenna on 145.625MHz and got SWR of 1:1.3 with quiet lengthy 50Ω RG-58 cable. With high quality shorter cable I archive SWR of 1:1.1 - 1:1.2.

100W RF dummy load  

100W RF dummy load

This is 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 resisters manufactured by Vishay Sfernice and both these resisters are connected in parallel to archive 50Ω impedance.

Outer-casing (which also act as 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.

Above mentioned 100Ω 50W power resisters are obtained through Farnell element14.

Assembled 455 kHz BFO module  

455 kHz BFO for SSB Reception

This post is about beat frequency oscillator (BFO) module which is used to receive SSB and CW signals from ordinary shortwave radio receiver. This module mainly consists with two general purpose NPN transistors and commonly available 455 kHz ceramic resonator.

In our testing we got quiet good results with this BFO on National Panasonic RX-5090T and some of the recorded samples are available at this soundcloud profile. Our modified schematic and PCB design is available to download at google drive.

Final view of modified HD-1410 electronic keyer  

Modified Heathkit HD-1410 electronic keyer

In this project we redesign original HD-1410 electronic keyer with today's commonly available components. In this new design the key components which we replace are transistors, diodes and power supply section of original HD-1410 circuit. Most of the NPN transistors in original design are replaced with KSP42 and KSP10 transistors, and all the PNP transistors are replaced with KSP92 transistors. To keep everything simple we also use same TTL chip-set with this new design. Schematic, PCB and wiring diagram of this modified HD-1410 keyer are available to download at my blog.

ICOM IC-R71A receiver restoration  

ICOM IC-R71A communication receiver restoration project.

This page contains article about ICOM IC-R71A HF multi-mode receiver restoration project. I got this ICOM IC-R71A receiver from one of my friend and when it comes to my workshop it's completely dead. After recapping and fixing some dry-joints this receiver starts to work again.

13.8V - 5A power supply  

13.8V - 5A Power supply unit.

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. I mainly build this power supply unit to power some of my amateur radio circuits and modules. This power supply unit is based on LM338 5A voltage regulator and MC3423 crowbar sensing circuit.


Other radios, transmitters and related projects

This section contains some radio, transmitter and RF based projects which are not directly related with amateur radio. More details of these projects are available in my blog.
Low Cost and High Quality Stereo FM Radio Receiver
Digital audio amplifier with PLL synthesized FM radio
VHF Aircraft radio communications receiver
Low power BA1404 base FM stereo transmitter
Two transistor superheterodyne shortwave receiver
CD2003 base simple FM radio receiver
Another TEA5767 based FM stereo radio receiver
Simple crystal tester
CXA1191S FM radio receiver
1750Hz tone generator