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80W RF Amplifier 88-108 MHz
Posted on Wednesday, June 22, 2011   •   Category: FM Transmitters


This is 80W RF power amplifier that boosts FM Transmitter's power using 2SC2782 bipolar transistors in a tuned class C circuit. RF amplifier can be driven to full 80W power with less than 1 watt driving input power, so that a large gain margin results in this FM transmitter. To obtain stability in this RF amplifier, I employed several techniques, such as placing the resonances of base and collector chokes far apart, damping the chokes with resistors, using RC combinations for absorption of unwanted frequencies, using feed trough capacitors for bypassing on the board, etc. It took some tweaking, but the amplifier ended up unconditionally stable.


TV Video Transmitter
Posted on Monday, June 20, 2011   •   Category: TV Transmitters


This is a TV transmitter for transmitting video of various video sources such as video cameras, Satellite receivers, DVD players, game consoles, etc. TV transmitter's circuit is working on the 470-580 MHz frequency and can be received on UHF channels 21-34. TV Video transmitter can radiate as far as 300 meters by using a 10-20 cm wire antenna. TV transmitter requires voltage of 9-15 Volts. However, you can also use a 9v batteries. Oscillator is based around BF199 and BFR90 RF transistors. If needed the range of TV transmitter can be extended by replacing BFR90 with 2N3886 transistors.


Bootloader for 16F87x PIC Microcontrollers
Posted on Saturday, June 18, 2011   •   Category: PIC


A bootloader enables download of hex-files directly into the flash-memory of a PIC or other microcontroller. The bootloader receives the user program via the PIC's UART and writes it directly to the program memory (self programming). This feature greatly speeds up the development process, because the chip remains in the target circuit and need not be moved between the target circuit and the programmer. When no bootloader is installed, all memory in the PIC can be utilized for user programs. That is 4 K for the 16F873 (0x000 to 0xFFF). Installing a bootloader means, that some part of the memory is occupied by the bootloader. The user can download his program into the remaining memory space. The bootloader in figure 1 occupy 256 words (0xF00 to 0xFFF), that is 6 % of the memory in a 16F873. The disadvantage of loosing 6 % memory is little compared to the advantage of fast program download and more friendly development routines.


RF Field Strength Meter with Attenuator up to 200 MHz
Posted on Friday, June 17, 2011   •   Category: FM Transmitters


RF Field Strength Meter with Attenuator up to 200 MHz The RF field meter unit is a great help to tune transmitters for best performance and output power. You can measure the radiated energy field and can easy tune the system for max output field strength maximum power. This field strength meter comes with selectable attenuator. You can use it for measuring the antenna gain and pattern, compare different magnetic field strengths. See the following RF field strength meter schematic.


8W Broadband FM RF Amplifier
Posted on Friday, June 17, 2011   •   Category: FM Transmitters


Here's 8W broadband FM RF amplifier using 2SC1971 VHF power transistor. The RF Amplifier PCB layout designed for FM broadband 88-108 MHz transmitters using microstripline technique. This 8W RF amplifier circuit provides an appropriate power boost for transmitters with an input of 500 mW.


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