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Long Range FM Transmitter
Posted on Thursday, July 7, 2011   •   Category: FM Transmitters

Long Range FM Transmitter

Presented here is a Long Range FM Transmitter. This circuit is a super-sensitive, mini-powered FM transmitter consisting of a RF (radio Frequency) oscillator section interfaced with a high sensitivity, wide pass-band audio amplifier and capacitance mike with a built-in FET (Field Effect Transistor) that modulates the base of the RF oscillator transistor. Transistor Q1 forms a relatively stable RF oscillator whose frequency and is determined by the value of coil L1 and turning capacitor C4.




2km TV Transmitter
Posted on Wednesday, July 6, 2011   •   Category: TV Transmitters

2km TV Transmitter

Here is a simple TV transmitter. The circuit is simple and really quite crude, but it does include MONO sound. I have not shown the two regulators in the drawing. These are one 12v DC 1A series regulator chip, and one 8v DC 1A series regulator. I fed the 8v regulator from the output of the 12v regulator. The rest of the circuit looks like this. It is a free-running Variable Frequency Oscillator (VFO) using just one coil and one capacitor to determine the frequency. Change this as you will. The basic circuit uses a 150pf from the Base of the RF transistor to ground, so that TR2 operates as a "common-base mode" (grounded base) amplifier. The tuned circuit in the collector and the capacitor from collector to emitter provide tuning and feedback.




Camera VHF Video Transmitter
Posted on Wednesday, July 6, 2011   •   Category: TV Transmitters

Camera VHF Video Transmitter

This is a simple video transmitter that can transmit as far as 50 meters. This video transmitter can be used with the camera or other video sources. You can view them on VHF channel analog TV. Supply voltage to the video transmitter can use 9V battery. Transistor components that are used for a video transmitter is BC548 or you can use another type of transistor BF199. Meanwhile, other passive components used SMD type. For winding coil L1 is 5 Turns 8 mm in diameter and use wire AWG 0.3-0.5 mm.




AVR Programmer
Posted on Tuesday, July 5, 2011   •   Category: AVR

AVR Programmer

Here's AVR programmer for programming AVR microcontrollers such as the AT90S1200 via the parallel port. AVR programmer is extremely simple. IC1 provides buffering for the signals that travel from the parallel port to the microcontroller and vice versa. This is essentially everything that can be said about the circuit. The two box headers (K2 and K3) have the ‘standard’ ISP (in system programming) pinout for the AVR controllers. The manufacturer recommends these two pinouts in an attempt to create a kind of standard for the in-circuit programming of AVR microcontrollers. These connections can be found on many development boards for these controllers. The software of AVR programmer carries out the actual programming task.




RF Inductance Meter
Posted on Tuesday, July 5, 2011   •   Category: Test and Measurement

RF Inductance Meter

This RF inductance meter measures RF chokes in the 500 nH to 50 uH range. I needed a way to measure hand-wound RF inductors in my second lab, and since I would only be doing this occasionally, I didn't need anything fancy, and since once a friend finishes his AT90S1200-based design, I plan to make one myself, I figured I'd use this for less than a year, so I didn't want to invest a lot of time in making it . I had run across the forerunner of this circuit, one that is more sophisticated in that it has a zero adjustment and range switch, but it was limited to higher inductances. I adapted it to the components I had on hand and changed it so that it would work in the 500 nanohenry to 50 microhenry range.The original circuit was reportedly published a few years ago by the Amrican Radio Relay League, so it is with appreciation of the ARRL that I make this circuit available.




Hybrid Tube Headphone Amplifier
Posted on Monday, July 4, 2011   •   Category: Headphone Amplifiers

Hybrid Tube Headphone Amplifier

Here's a simple to build hybrid tube headphone amplifier built around 12AU7 / ECC82 vacuum tube. I have always been intrigued by tube amplifiers, but most DIY kits are very expensive and use very high voltage. So I decided to build an amplifier that would be inexpensive and had the least amount of parts necessary to drive a pair of 32 ohm Grado headphones. Having built several YAHA amps based on the fa-schmidt design, and a Szekeres Mosfet follower I wondered how the two would sound together. So I built the schematic into TINA-TI, a free spice based program to test circuits before the build, and the results were remarkable. Nearly 20dB of gain across 20Hz-100kHz from a 13VDC power supply. As you see in the schematic and parts list, there are less than 30 discrete components and most DIY'ers will have them as spares from other builds. I chose the 12AU7 / ECC82 vacuum tube because it can be driven with low voltage and the filament voltage is 12.6 volts, so there is no need to regulate the voltage any further. I used 1/4W resistors in the first stage and 2W in the second. The 2W resistors may be overkill but I did not want to change them later. The 20ohm resistor must be a minimum of 5W and do not use wire wound, as the inductive characteristics will distort the response curve.




Inductance Meter
Posted on Saturday, July 2, 2011   •   Category: Test and Measurement

Inductance Meter

This is inductance meter I built using 74HC14 IC. Initially I used a DMM as the display device, but on a whim I tried hooking up a moving-coil meter. To my surprise, it actually worked just fine, 1K in series was sufficient to allow a useful calibration and didn't overload the drive capabilities of the last gate in the package. I calibrated my unit for 0-100 uH, as this is the range I am generally most interested in, and it gives direct-readings on the uA scale of the meter. With the values as Dick specified, there is sufficient range to calibrate it from about 25 uH to 250 uH FSD.




100W Transmitter RF Power Amplifier 2SC2782
Posted on Thursday, June 30, 2011   •   Category: FM Transmitters

100W Transmitter RF Power Amplifier 2SC2782

This is a 6m band transmitter RF power amplifier (50 MHz) with 100W output. It used with my FT-736R and drive from 10W for the 6m SSB DX. The Building information comes from Japan CQ Magazine. The Toshiba RF bipolar power transistor is used in it. If you want to construct this rf amplifier, it's the better way if the double side PCB use for increase the grounding and current transfer. The TX power can be tune to 120W.




USB Sound Card with PCM2902
Posted on Thursday, June 30, 2011   •   Category: Audio DAC

USB Sound Card with PCM2902

This is USB sound card with PCM2902 chip. For the purpose of testing the D / A converters, I built a simple USB sound card with the circuit PCM2902. The card has analog input and output, an electrical S / PDIF output, galvanically separated input and optical input and output TOSLINK. The heart of USB sound card is PCM2902 it is a circuit connection, which is a complete USB codec. The circuit can handle up to 48kHz sampling frequency. The integrated circuit includes a USB controller for A / D and D / A converter, HID part for 3 buttons, volume control, custom converters and S / PDIF encoder and decoder.




200W Leach Amp
Posted on Wednesday, June 29, 2011   •   Category: Amplifiers

200W Leach Amp

This article describes how to build 200W Leach Amplifier from Mr. Marshall Leach known like “The Leach Amp”. Article about building of this amplifier I found later in journal A_Radio Praktická elektronika 11/2002. For many years I looked for construction of HiFi amplifier wit a good parameters, enough power reserve and simple construction. I built a couple of amplifiers with integrated circuits MBA810, TDA2005, LM3886, but I was disappointed by their output quality and noise. I decide to built a classic construction with discrete components and bipolar transistors. Construction from Mr. Dudek was interesting, but I didn’t like used components and complexity. All of my requirements satisfied construction of the Leach Amp. Circuit author publicates in a February 1976 in american journal. From these days circuit was not practically changed. Little changes are described on authors page. I succeeded to find almost all original components on our local market, which was a miracle. Only a bigger problem was a power transformer and filter capacitors. Recommended toroid transformer for power 200W to 4 ohms is 230V/2x 42V.




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