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Modulator Circuits
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Last Updated: November 21, 2017 05:47 AM

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3 Watt FM Transmitter   -  This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz.  Although the stability isn't so bad, a PLL can be used on this circuit.  This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power.  From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05   (quite normal at my place with my antenna).   __  Designed by Aaron Cake

300 MHz AM RF Remote Control System   -  If you plan to build this project, simply replace the RE-99 receiver & TX-99 transmitter with the RWS-434 & TWS-434A RF receiver & transmitter modules found HERE.  These circuits will work with any RF transmitter and receiver modules.  Due to the huge interest in this project, I have just recently finished the NEW schematics.  The older schematics were scanned and pretty poor quality.  These new ones should make it considerably easier to recognize the parts used for the project.   __  Designed by © Reynolds Electronics

300 MHz Prescaler   -  A preamp that drives the CMOS counter input and a divide by 10 prescaler to extend the range of A Little More Serious Frequency Meter.  The MCT10280 prescaler can be set to divide by 80, 40, 20, or 10, as a function of which pins are tied to the power supply.  I set this one to divide by 10 since it is adequate for my needs, and the mental calculation of multiplying the meter reading by 10 is not taxing.  One problem with the MCT10280 is that if it doesn't have an adequate input, the output is very noisy, which shows up as counts in the couple MHz range on the frequency meter.  This noise shows up if the signal amplitude the signal frequency is too low.  For this reason, I only intend to use the prescaler with inputs between 10 MHz and 300 MHz __

300m FM Transmitter   -  This FM transmitter circuit is very simple and it has a acceptable transmission .  The signal transited from this FM transmitter circuit can be received at almost 300 meters in open air .The circuit require a 3volts operating voltage and can be tuned anywhere in the FM band.The coil should be about 3mm in diameter __

300m FM Transmitter   -  This FM transmitter is about the simplest and most basic FM transmitter it is possible to build and have a useful transmitting range.  It is surprisingly powerful despite its small component count and 3V operating voltage.  It will easily transmit over 300 meters in the open air and even more with higher voltage supply.  The circuit we use is based on a proven Australian design.  It may be tuned anywhere in the FM band.  Or it may be tuned outside the commercial M band for greater privacy.  Of course this means you must modify your FM radio to be able to receive the transmission or have a broad-band FM receiver.  The output power of FM transmitter is within the legal limits of many countries.  However, some countries may ban all wireless FM transmitters without a license.  It is your responsibility to check the legal requirements for the operation and to obey them.  FM transmitter is constructed on a single-sided printed circuit board PCB. __

300mW FM Transmitter with 2SC2538   -  The above FM transmitter has RF output power of 300 mW and covers more than one kilometer distance.  Frequency adjustment is accomplished with MV2105 varactor diode and R7 10K potentiometer.2SC2538 is a class C 300mW amplifier. __

30W VHF FM Amplifier for 88-108 MHz with BLF245 MOSFET   -  The achievement of this 30-watt amplifier has been designed to take place on a heatsink microprocessor PC equipped with its fans, the advantage of this method of cooling has been selected for the fact that   (French  __

3V FM Transmitter   -  The objective of this 3V FM Transmitter design is to provide a simple low-power transmitter solution for broadcasting audio from various audio sources.  This transmitter transmits audio using small sensitive microphone.  Transmitter's frequency, as built is tunable via 15pF trimmer to the desired frequency, and the coil is embedded on the circuit board.  This implementation is adapted to rebroadcast the output of a CD player, television receiver, or radio receiver.  I use this transmitter so that I can move about the house and listen to my favorite programs without disturbing others.  Within and the house, I find that I can get 50 to 100 meters away from the transmitter with the small pocket FM receiver I carry in my shirt pocket. __

3V FM Transmitter for 88MHz to 108MHz   -  The important part of the circuit is formed of the Colpitts type oscillator.  C3, C4, C5, C6, CD1-CD2 and L1 determines the frequency.  BF982 and dual gate MOSFET are active parts in oscillator.  When the input impedance of the MOSFET gate inputs are high, LC tank is not affected.  However transistors force the LC tank and cause phase shift.  Two driver stages are added to isolate the antenna from oscillator.  First stage   (BF199) amplifies the low signal of the oscillator and works as a constant load.  The second stage   (BFR90) amplifies the signal going through the antenna some more.   __

3W FM Transmitter   -  This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz.  Although the stability isn't so bad, a PLL can be used on this circuit.  This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power.  From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05   (quite normal at my place with my antenna).   __  Designed by Aaron Cake

4 MHz Amplitude Modulated RF Source   -  A while back I needed an amplitude modulated signal source at 4 MHz.  This circuit was literally thrown together with parts laying on the bench.  I built it dead bug style on a piece of copper clad board.  It should work with little or no modification, other thano get it to oscillate, and at higher frequencies, you might have to reduce the capacitor values a little.  Just be __  Designed by Dick Cappels

4 Transistor FM Receiver   -  This is a pocket sized receiver I built in 1994.  The idea was to make a simple but useable receiver running off 3V.  My previous 6 transistor receiver was more bulky, requiring 12V.  This meant 10 x AA cells.  I designed and made a PCB, .   __  Contact blehack @ yahoo dot com

4 Watt FM Transmitter   -  This is a small but quite powerful FM transmitter having three RF stages incorporating an audio preamplifier for better modulation.  t has an output power of 4 Watts and works off 12-18 VDC which makes it easily portable.  It is the ideal project for the beginner who wishes to get started in the fascinating world of FM broadcasting and wants a good basic circuit to experiment with __  Designed by Gundalla

4 Watt FM Transmitter   -  The following is a simple yet powerful 4W FM transmitter which is tunable to 88-108MHz frequency.  Connect to your ipod/computer, etc.  When this was first made, I only had a 2N2219A on hand, which resulted in a lower RF output.  I have since swapped out the transistor for a 2N3866 for full 4W output at around 15VDC supply.  In order to achieve a high output level, you will need a well tuned antenna, and a large heatsink to dissipate the heat from T2 transistor.  Transmitter was mounted in metal enclosure and works extremely well. __

40 Meter Direct Conversion Receiver   -  Using the circuit of direct-conversion receiver described here, one can listen to amateur radio QSO signals in CW as well as in SSB mode in the 40-metreband.  The circuit makes use.   __

40 Meter Popcorn Superhet Receiver   -  schematic for a no-frills, relatively low-cost CW superhet receiver with a 4.00 MHz Intermediate frequency.  There is no AGC or RF gain control, however this receiver has good large signal handling capability.  This receiver uses just 6 bipolar transistors and an op amp for reasonable volume into headphones.  Much __  Designed by VE7BPO

40 Meter, 5 Watt QRP Transmitter   -  As ham operators, we like to broaden our horizons by trying something new.  There is nothing more satisfying about this hobby than building your own transmitter.  The circuit in figure 1 is a crystal controlled CW transmitter with at least 5 watts of power.    (The prototype generated 7 ˝ watts) This circuit was built on a Radio Shack universal board   (276-168B) and worked extremely well the first time __  Designed by Radio Amateur Society of Norwich

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   -  Schematic + Parts List + PCB __   Jan Kolar

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. __

4-Transistor Transmitter   -  4 Transistor Transmitter - Circuit + Parts Lits + Notes __  Designed by Paul C. Sherby

4W FM Transmitter   -  Schematic + Parts __  Contact Kyriakos Kontakos

4W FM Transmitter   -  As it has already been mentioned the transmitted signal is Frequency Modulated   (FM) which means that the carrier’s amplitude stays constant and its frequency varies according to the amplitude variations of the audio signal.  When the input signal’s amplitude increases   (i.  e.  during the positive half cycles) the frequency of the carrier increases too __  Designed by Kamran Ahmed-UK

4-Watt AF Amplifer   -  I have recently included a page about AF amplifers for use with Homebrew rigs.  In this I mentioned that I may include a practical one-watt circuit, complete with PCB foil and layout.  Here it is, but I have taken the liberty of engineering it to provide 4-watts of AF output and with a frequency response almost suitable for Hi-FI applications __  Designed by Harry Lythall-SM0VPO

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


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