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 Schematics  >> 

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4 Transistor FM Transmitter
This circuit provides an FM modulated signal with an output power of around 500mW. The input microphone pre-amp is built around a couple of 2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset trim potentiometer. The oscillator is a colpitt stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor. The output stage operates as a 'Class D' amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.


40 Watt FM Transmitter Amplifier
Building two stage 40 Watt FM Transmitter Amplifier. RF input power should be between 0.5 and 1 watt. Amplifier is powered by 28V power supply. The diagram shows a 2N3375 driving a 2N5643 but there are many other transistors that will work. I used these two transistors just because they were cheap at the time. If any of the variable capacitors are at full capacitance you can pad them out with a fixed ceramic capacitor of suitable value. Extra capacitance also might be needed on the base of the transistors (i had to add 3 100pF capacitors on the base of the 2N5643). The transistors are bolted to a piece of right angle aluminum which is fixed to the metal chassis to dissipate heat effectively.


400mW VCO FM transmitter
With good antenna (dipole placed outdoor and high) the transmitter has very good coverage range about 500 meters, the maximal coverage range is up to 4 km.


40mW FM TRANSMITTER
The transmitters on my homepage seem to be quite popular, especially those intended for the 88 - 108MHz FM band. I must really confess that I also favor this broadcast band, mainly because it is so easy to find signals on the workshop radio. Everyone has an FM radio, and it is fun to play with. Experimental antennas and the like can all be developed in this band since there are a huge range of "beacons" all transmitting just for my benefit :-). Basic oscillators also are easy to fault-find in this frequency band, and then later modified for other VHF bands. The V5 FM Wireless Microphone is a 10mW transmitter that featured a coil fabricated on the PCB itself. This made the project easy to duplicate and removed "microphony" (the ability of coils to act as a microphone with spring-line reverb). But as several people have already commented, although more stable than most other similar kits and projects, the frequency still does vary with battery voltage. In just one session it can vary by 200kHz when a cheap "Mighty Atom" battery falls to 8 volts.


4km FM Transmitter
This is a VCO FM Transmitter. With good antenna (dipole placed outdoor and high) the transmitter has very good coverage range about 500 meters, the maximal coverage range is up to 4 km. To calibrate for maximum power connect 6 V / 0,1 light bulb to the output and use R1 to tune the right frequency, adjust L1 coil if necesary. Then use C14 and C15 to adjust the highest power (the highest light of the bulb). Then you can connect antenna and audio signal. Adjust R2 until the audio sounds as loud as the other stations.


5 Watt FM Amplifier
This design is a 2 stage amplifier that has about 17db of gain, suitable for an input of 50 to 100 MW. Its basically a Veronica 5 watt vco transmitter, without the vco. The transistors are a 2N4427 and a MRF237. Output power is 2.5 to 5 watts, depending on input drive and dc voltage. At 13.7 vdc with 50 MW of drive, the output was 2.5 watts. The maximum dc voltage recommended is about 15-16 volts.


5 Watt Transmitter
This is a very simple 5 watt CW TX based upon a TTL logic chip. There is just one "tricky" component and this is Cx. This component should have an impedance of about 10 - 50 ohms at the frequency of interest. If you wish to reduce the transmitter power, increase the value of Cx. It is Cx which causes the square wave from the output transistor to approximate a sine waveform. The value of Cx is the price of simplicity in this TX.


5 Watt UHF TV Amplifier
This small circuit is a Linear amplifier for driving small UHF TV transmitters. Its gain is 7dB and can amplify a signal between 450-800 MHz. You can drive the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth. Use a stabilized power supply 25 volts and at least 5Amps. The transistor case is the SOT-122A and be careful because the transistor is very toxic for your health. Tuning can be achieved turning the two variable capacitors. Do not forget to use heat sink for both transistors, specially for the BLW89 and it would be better if you place a small fan as well.


5 Watts FM RF Amplifier
This fm rf amplifier uses 2SC1971 transistor to provide 5 watts of output. Output matching is adjusted via the two 40pF trimmer capacitors likewise also to the input. Note that the emitter of this transistor is directly grounded on the heat sink and should have a good thermal transfer. Driving power of 100 to 200mW can be applied in order to provide 5watts of output. Use a dummy load to tune this amplifier and remember that the transistor is biased in Class C, sufficient filtering should be followed after the output to minimize all the harmonics. Use ground plane construction technique in the PCB lay-out for best result, the more the grounding the better. If you have hard time finding the 10uH rf choke, try to wind 1/2 meter of 0.2mm enamel wire over a 33K 1/2 watt resistor and solder the coil ends to the legs of the resistor.


500mW Broadcast FM Transmitter
This little broadcast FM transmitter has 500mW of RF output power and runs of 12-15V battery or power supply. DC whose signal modulated by FM using four transistors. Transmitter includes four transmitter stages and draws around 100-150mA of current. Using the values of the circuit components, the frequency will be around 100 MHz but can be changed via coil. Through the 5 pF capacitor and 10K ohm resistor, the modulation of audio signal is supplied to the tank circuit. The amount of modulation is being managed by the 1N4002, a general purpose rectifier diode. FM Transmitter's output stage is functioning as a class D amplifier where the output transistors act as a switch.


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Accurate LC Meter Capacitance Inductance Meter with 16F628 and LCD
Volt Ampere Meter with 16F876 Microcontroller and LCD display
 
Accurate LC Meter

Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings.
PIC Volt Ampere Meter

Volt Ampere Meter measures voltage of 0-70V or 0-500V with 100mV resolution and current consumption 0-10A or more with 10mA resolution. The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored. The meter uses PIC16F876A microcontroller with 16x2 backlighted LCD.

50MHz 60MHz Frequency Meter / Counter with 16F628 & LCD
1Hz - 2MHz XR2206 Function Generator
60MHz Frequency Meter / Counter

Frequency Meter / Counter measures frequency from 10Hz to 60MHz with 10Hz resolution. It is a very useful bench test equipment for testing and finding out the frequency of various devices with unknown frequency such as oscillators, radio receivers, transmitters, function generators, crystals, etc.
1Hz - 2MHz XR2206 Function Generator

1Hz - 2MHz XR2206 Function Generator produces high quality sine, square and triangle waveforms of high-stability and accuracy. The output waveforms can be both amplitude and frequency modulated. Output of 1Hz - 2MHz XR2206 Function Generator can be connected directly to 60MHz Counter for setting precise frequency output.

BA1404 HI-FI Stereo FM Transmitter
USB IO Board PIC18F2455 / PIC18F2550
BA1404 HI-FI Stereo FM Transmitter

Be "On Air" with your own radio station! BA1404 HI-FI Stereo FM Transmitter broadcasts high quality stereo signal in 88MHz - 108MHz FM band. It can be connected to any type of stereo audio source such as iPod, Computer, Laptop, CD Player, Walkman, Television, Satellite Receiver, Tape Deck or other stereo system to transmit stereo sound with excellent clarity throughout your home, office, yard or camp ground.
USB IO Board

USB IO Board is a tiny spectacular little development board / parallel port replacement featuring PIC18F2455/PIC18F2550 microcontroller. USB IO Board is compatible with Windows / Mac OSX / Linux computers. When attached to Windows IO board will show up as RS232 COM port. You can control 16 individual microcontroller I/O pins by sending simple serial commands. USB IO Board is self-powered by USB port and can provide up to 500mA for electronic projects. USB IO Board is breadboard compatible.

RF Remote Control 433MHz Four Channel
100m 4-Channel 433MHz Wireless RF Remote Control
 
200m 4-Channel 433MHz Wireless RF Remote Control

Having the ability to control various appliances inside or outside of your house wirelessly is a huge convenience, and can make your life much easier and fun. RF remote control provides long range of up to 200m / 650ft and can find many uses for controlling different devices, and it works even through the walls. You can control lights, fans, AC system, computer, printer, amplifier, robots, garage door, security systems, motor-driven curtains, motorized window blinds, door locks, sprinklers, motorized projection screens and anything else you can think of.
100m 4-Channel 433MHz Wireless RF Remote Control

Four button RF remote is used to turn ON / OFF four different devices independently. Any of the four outputs can be configured to work independently in either toggle or momentary mode. Outputs are buffered by BC549 NPN transistors and can drive low voltage devices directly or be connected to either 5V or 12V relays (or motors) to control appliances that use 110V / 220V mains voltage or any voltage of your choice. Multiple remote systems can be used independently to control more than four appliances in the same location by changing the address code on 433MHz receiver and remote. It is also possible to use several remotes to control the same appliance such as garage door.
 
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