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 .

I got Trio ( now Kenwood ) JR-310 and TX-310 SSB receiver and transmitter pair recently. When it comes to me both receiver and transmitter are in very bad shape and most of the PCBs and chassis are covered with dust and some of the components are very badly damaged. After examining both the chassis I decided to repair both units because of its vintage value (and also I like to try some tube base SSB receiver and transmitter pair). Trio JR-310 is AM, SSB and CW mode HF receiver. This receiver has 3.5, 7, 14, 21, 25 and 50MHz operating bands and sensitivity is around 1µV. This receiver consists with 6 vacuum tubes, 5 transistors and 19 diodes. JR-310 which I restored is working with 110V and total power consumption is around 70W. Bottom view of restored JR-310 receiver TX-310 is 20W SSB transmitter and designed to match with JR-310 receiver. It is capable of LSB, USB, AM and CW transmissions in HF bands. This unit consists with 10 vacuum tubes, 5 transistors and 9 diodes. Like ...

In this project we introduce portable microprocessor controlled CW radio beacon. This CW beacon module is capable to transmit maximum of 64 Morse codes repeatedly in 4.433MHz with 9V DC power source. This system consists of CW transmitter, ATtiny13 microcontroller unit and low current voltage regulator. Atmel ATtiny13 microcontroller is used to drive the transmitter and thanks to its internal 64 byte E²PROM, we may be able to change beacon data without altering the system firmware. While at the testing stages we receive this beacon on 10km radius (using Sony ICF-SW7600GR receiver) by using standard telescopic antenna. To get the maximum range it is recommended to use 3m – 4m antenna wire with this transmitter system. At the prototyping /testing stages we try this transmitter successfully with 3.58MHz, 4.43MHz and 6.00MHz crystals. This system is design to work with standard 9V battery (6F22/6LR61). At the prototyping stages we test this system using 12V and 10V DC power sou...