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Modulator Circuits
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Last Updated: October 24, 2017 02:55 PM

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Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

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 HF CW 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 __  Designed by Harry Lythall-SM0VPO

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 AM transmitter for the 20 meter band (14MHz)   -  In this project, you will make a simple low-power broadcast-type circuit, using a crystal oscillator integrated circuit and an a collector modulated AM oscillator. You can connect the circuit to the an electrec microphone (pointed out in gray on the diagram) or amplified dynamic microphone (no amplified microphone has a to low output voltage to work. Approx. 100mv is needed). You could also add a LF preamp stage of one transistor to allow connecting a dynamic microphone directly. __  Designed by Guy Roels ON6MU

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. __

500mW FM / VHF Transmitter Amplifier / Booster   -  High performance low noise 500mW amplifier / booster for all low power FM transmitters such as BA1404, BH1417, BH1415, 433MHz transmitter modules, etc.  The amplifier chip is an integrated circuit containing multiple transistor stages and all other parts conveniently within a single small package.  Boosting your FM transmitter has never been easier and the output signal can also directly drive 2n4427 or 2n3866 transistors for 1W or 5W of RF output power. __

50mW BH1417 Stereo PLL FM Transmitter   -  This is an excellent 50mW Hi-FI PLL FM Stereo Transmitter that features BH1417 chip.  ROHM's new Japan has BH1417 is one of the most simple and practical integrated circuits, which combines phase-locked loop circuit, stereo encoder circuit, transmitter circuit, as well as other additions.  Pre-emphasis circuit, limiter circuit and low pass filter can significantly improve the sound quality.  The total harmonic distortion up 0.3%, stereo separation to 40dB, RF output level is 100dB.  BH1417F is an excellent new IC chip, this circuit improves signal to noise ratio   (S / N) of pre-emphasis circuit to prevent signal over emphasized limiting circuit, the control input signal frequency low-pass filter circuit   (LPF), generate stereo stereo composite signal modulation circuit, FM transmitter phase-locked loop circuit   (PLL) component.  BH1417F excellent frequency characteristics, it can achieve 40dB of isolation, transmitted sound quality is similar to local FM radio stations. __

5W PLL Stereo Transmitter with LCD   -  Here's PLL FM transmitter circuit from china.  This circuit uses the familiar 2SC1971 for final power amplifier stage.   __  Contact sky @ cantonmade.com and balalove2008 @ hotmail.com

6 Transistor Super Regen Receiver   -  Solid State Superregenerative Receiver.    This is the only solid state super regen design with more than 20uV sensitivity on FM that I know of.   __  Contact blehack @ yahoo dot com

6 Watt FM Transmitter Amplifier   -  After building FM transmitter I decided to build a 6W RF Transmitter amplifier for the FM band to get more power and we chose to copy a 6 Watt design built around 2SC1971 RF power transistor.  We were not satisfied with finished result and decided to replace the fixed capacitors around the pcb inductors with variable capacitors, this is much better and possible to tune to your transmitter frequency. __

6W FM Transmitter 88-108 MHz   -  Presented FM transmitter is built around low power PLL transmitter and amplifier that boosts its signal all the way up to 6 Watts.  The signal is amplified by three RF stages of amplification.  In the first and second stages of the transmitter one of the best driver transistors were used 2SC2053.  You can use the other transistors but only up to 500mW of power.  In the third stage 2SC1971 RF transistor was used to achieve 6W of power.  For making any RF transmitter circuit at least two meters are necessary, one is frequency counter and the other is RF field strength meter for which the schematic is provided. __

7 Watt FM Transmitter   -  This 7 Watt FM Transmitter was originally a 200mW unit, without the universal power stage added.  Together with the power amp 2SC1971 / MRF237 / NTE342 it then became a 7W unit.  I used this transmitter with a half-wave open-end dipole in a vertical position 50 feet above ground.  Together with about 70 feet of coax, this transmitter delivered great audio at a distance of 10 miles   overall distance was 17 miles, but the audio signal was weak.  I had no equipment, other than a watt meter to measure it's power and a digital FM tuner with a 5-LED Signal Strength Bargraph display to use as capturing the main oscillating frequency, which was right at 87.5 MHz.  This circuit worked well for me, as I had experimented with it for nearly a year.  Of course, one would be better off with more equipment than I have had to capture the main oscillating frequency.  That was, by far, one of the hardest things to capture.  It was thru trial and error, with the FM tuner, in finally finding out how to grab the right frequency.  When I finally did get used to find out where my 'main' frequency was, the unit performed extremely well.  Like I had said above, right at 10 miles, the unit was at its best giving clear audible audio into the speakers of my car.  With the transmitting antenna at 50 feet above ground, I decided to see how well I could receive the transmitter signal from an overpass than is exactly 15 miles from the transmitter.  When I got to the top of the overpass in my car, the audio signal came in as 'clear as a bell'.  I now understand what is meant when one says FM signal travels best in a line of sight.  Well, being on that overpass, if I had a strong telescope with me, I am sure I could see the 50 foot antenna in my oak tree.  So with the overpass being right around 50 feet in height also, the transmitter surpassed my judgement call on its signal.  I surrender this circuit to anyone who likes to experiment in things like this.  Enjoy! __

70-120MHz FM Receiver   -  This simple one chip FM receiver / TV tuner will allow you to receive frequencies from 70 up to 120MHz.  With this small receiver it is possible to pickup TV stations, entire 88, 108MHz FM band, aircraft conversation and many other private transmissions __

76-110MHz FM Radio Transmitter   -  Here is a simple 76-110MHz FM transmitter that can transmit your voice or audio over an ordinary FM radio within the FM broadcast band.  It can transmit both voice using microphone and music from any music player.  Frequency is changed by adjusting 5.5 turn inductor coil.  Transmitter is powered by 9V battery or 3V-9V power adapter.  Transmission range is 100 meters but can be increased with better antenna or RF amplifier. __

76MHz-110MHz FM Transmitter with Booster   -  Three stage FM transmitter with an on board signal booster for increased transmitting range.  It broadcasts audio on 76MHz - 110MHz FM frequency via included on board microphone or from MP3 player, Phone, iPod, Computer, Laptop, CD Player, TV, Satellite Receiver via on board 3.5mm connector.  It transmit sound with excellent clarity throughout your home, office, yard, camp ground, etc.  Transmitter is supplied by 3-12V DC voltage and uses one 2SC9014 and two 2SC9018 low noise RF transistors. __

80 MHz-108 MHz FM Transmitter   -  FM transmitter or often called fm transmitter uses 2 transistors in this article uses 2 transistors 2n2222.  If the fm transmitter is in use voltage supply of 9 volt battery and use an antenna whose length is less than 12 inches, then this fm transmitter will be within FCC limits.  Signals from the microphone in the fm transmitter is reinforced by Q1, Q2 with carrier frequency generator is determined by the C5 and L1.  The frequency of the FM transmitter is in the range 80 MHz - 108 MHz.  L1 can be made ​​with as many as 24 e-mail wire wrap and 6 wrap.  The following is a picture series for the fm transmitter fm transmitter referred to in article 2 of this transistor. __

80 Watt FM stereo transmitter   -  A high quality broadcast transmitter big enough for a medium town! __  Designed by Manfred Mornhinweg

8W PLL Stereo Transmitter with LCD   -  Very stable FM transmitter based on TSA5511 synthesizer.  Frequency is performed with three buttons through PIC16F84 microcontroller.  Frequency is displayed on 16x1 LCD.   __

98-108MHz FM audio transmitter   -  Schematic only __  Designed by Peter Jakab

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Modulators:  #'s - A        B - F        G - M        N - T        U - Z

 


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