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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:

New & Improved Islander using the NTE474 Transistor   -  The Islander is a 7-Watt LPFM transmitter using the NTE474 RF transistor.  Together with a half-wave dipole positioned in a vertical stance, the signal leaving the antenna will then radiate evenly in an omni-directional fashion.  With the antenna just at 15 feet above ground level, a signal distance of 3 miles can be achieved.  At an elevation of 50 feet above ground, a signal distance of 10 miles can be achieved.   __  Designed by braincambre500 @ yahoo.com

Noise-Muting FM Receiver   -  The tuning of a frequency-modulated (FM) receiver to an FM radio station frequency involves a lot of ‘hissing’ noise in between the stations, which is very irritating for the operator and___ Electronics Projects for You

One Tube FM Tuner   -  From August 1960 Popular Electronics, it uses a 6C4.  I constructed this project as closely as I could to the original.  Performance left a lot to be desired! __  Contact blehack @ yahoo dot com

One Valve FM Receiver with Loudspeaker   -  Using a single 6DX8, this receiver provides loudspeaker reception of FM stations __  Contact blehack @ yahoo dot com

One Watt AM transmitter for the 10 meter band (28MHz)   -  In this project, you will make a simple 3-stage low-power broadcast-type circuit, using a crystal oscillator integrated circuit and an a collector modulated AM oscillator with amplifier.  You can connect the circuit to the an electred microphone or amplified dynamic microphone.  Using an electred microphone is shown (in gray) in the diagram below.  (no amplified dynamic microphone has a to low output voltage to work.  at least 100mv is needed).  You could also add a LF preamp stage of one transistor to allow connecting a dynamic microphone directly.  You'll see that you can receive the signal through the air with almost any AM radio receiver.  Although the circuits used in radio stations for AM receiving are far more complicated, this nevertheless gives a basic idea of the concept behind a principle transmitter.  Plus it is a lot of fun when you actually have it working!  Remember that transmitting on the 10 meter band you'll need a valid radioamateur license!! __  Designed by Guy Roels ON6MU

One Watt Four Stage FM Transmitter   -  This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1) , a preamplifier built around transistor BF200 (T2) , a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4).  A condenser microphone is connected at the input of the oscillator.   __

One Watt RF Amplifier   -  This is a universal 1 Watt RF class C amplifier that is ideally suited for low power FM transmitters.  Input should be at least 100mW to achieve 1W output.  It is recommended to enclose the amplifier in a metal case.   __

One-transistor FM Transmitter   -  A truly minimalist circuit.  Performance is relatively poor and stability is a problem.  Q1 modulates the signal and acts as an oscillator.  L1 and C5 determine the frequency.  Decrease C5 for a higher frequency and vice-versa.   __

One-transistor Regenerative AM Receiver   -  A classic design revamped slightly.  Features a single-transistor regen stage, and a range of 1000 miles with a 4-foot antenna.  Perhaps the best "survival radio", yet.  Now updated with speaker amplifier.   __

Op Amp Based FM Transmitter   -  An low power FM Transmitter using an op-amp as the audio preamp and a single transistor as the RF amplifier.   __  Designed by Kamran Ahmed

Open Half-Wave Dipole Antenna Project for the FM Transmitters   -  I have used this special type dipole antenna with the 200mW FM Transmitter and the 7 Watt.  It has performed very well indeed.  Construction is fairly easy and the whole assembly is light-weight.  If you any questions concerning it or should you decide to make it, give me a call and I will help in any way that I can __  Designed by braincambre500 @ yahoo.com

Original Islander using the NTE342 Transistor   -  My design of the Islander came after one year of intense experimentation.  Formally, the last stage had 3 more variable capacitors.  but I took them out and adjusted their respective coils to a preset form.  thereby eliminating of having to adjust 5 variable capacitors.  My PCB design is a 'no hole' component mount.  The PCB does look rather worn __  Designed by braincambre500 @ yahoo.com

Parallel Port VHF FM Receiver   -  Use it to monitor the 144-148MHz amateur band, the 132-144MHz band or the 118-132MHz band.___ SiliconChip

Pen FM Transmitter Bug   -  Pen FM Transmitter bug projects have been very popular.  The idea of being able to hide a transmitter in a pen is very appealing.  In an effort to reduce the size of this design, we have used surface-mount components.  Firstly, the thought of using the coil in the tank circuit for transmitting RF was a little far fetched, but we used it as an example for those who were interested in experimenting with our circuits.  Now we have gone back to a conventional antenna, the whip.  The whip or straight-line antenna can be coiled, wound longitudinally or folded.  The way it is wound makes a big difference to its effectiveness, but when you are limited in space, you have to accept these limitations.  Even though we have used this antenna set up in our previous pen bugs we have considerably improved the circuit to the point were it has low battery consumption, but high RF output.  The size of this design has been reduced considerably by using surface-mount components. __

Phone FM Transmitter   -  This Phone FM transmitter connects in series to your telephone line and transmits the telephone conversation over the FM band when you pick up the telephone handset.  Transmitted signal can be tuned by any FM receiver.  The circuit includes an "On Air" LED indicator and also provides a switch which can be used to turn off the transmitter.  A unique feature of the circuit is that no battery is needed to operate the circuit since power is taken from the telephone line.   __

Pi Filter has Sharp Notch   -  Simple filter network makes a great low-pass filter having a sharp notch just outside paSSBand.  Can be implemented as active filter using GIC circuit.  Use this component calculator to determine resistor and capacitor values.  Voted best of issue! __  Designed by Jim Haggerman, Hagerman Technology LLC

Pi Section Coupler   -  Inexpensive gadget tunes antenna for better DX.  Almost any receiver covering 540 kHz to 1600 kHz is suitable for broadcast band DX'ing, and there are a lot of them.  But the antenna is another matter.  If you are new to the hobby, or if you have been having trouble DX'ing those really difficult stations, you may find the answer to your reception problems in a properly constructed long-wire antenna - and the "Pi-section Coupler" __  Designed by Roy A. Walton

PLL Exciter   -  This is a PLL controller that works with the VCO/Modulator that I designed.  Use these two modules together for a complete baseband-capable exciter unit.  This PLL controller features a rock-stable crystal controlled reference, in conjunction with a programmable dividing network which allows the transmitter to be tuned in 100Khz steps from 79.9Mhz to 109.7Mhz by means of digital thumbwheel switches.___ Electronics DIY

PLL FM Transmitter   -  This is PLL FM Transmitter using SAA1057 chip.  Transmitter can be operated from a PC through LPT port, or using a PC software as a driver. __

PLL Stereo FM Transmitter   -  The circuit shown here is of a good Stereo FM transmitter that can transmit high quality signals up to a range of 70 feet.  The circuit is based on BH1417 PLL stereo transmitter IC from Rhom semiconductors.  The IC has separate audio processing sections for the left and right channels, pre emphasis circuit for improving signal to noise ratio, crystal control circuitry for accurate frequency locking, multiplex circuit for making sum ( left plus right) and difference ( left minus right) {see this article for better understanding Stereo decoder circuit} etc.  Another important feature of this IC is that the transmission frequency can be set using a 4 channel DIP switch.  The IC can be powered from anything between 4 to 6V DC and has an output power around 20mW.  At full output power the circuit consumes only 20mA and has a channel separation of 40dB.There are 14 possible preset transmission frequencies, starting from 88.7MHz and incrementing in steps of 0.2MHz that can be selected using the DIP switch.  The PLL circuitry of the IC is so precise that there is practically no frequency drift. __

PLL Synthesized FM Transmitter   -  The functioning of all is provided by a microcontroller from MICROCHIP "PIC16F84" which provides support for buttons, LCD 2 lines of 16 characters and the circuit pll "SAA1057.  The VCO is entrusted to the transistor Q8 associate of his two diodes varicaps "BB109, a floor buffer Q7 separates the VHF signal obtained in two ways, on the one hand to Q9 to enslave loop phase and on the other hand to the Q5 and Q6 together which takes care to amplify the signal before attacking Q11, a "BFR96" which plays the role of HF switch via a timer "NE555" which receives information from the push and "SAA1057" ensuring HF cutoff in the event of failure of a locking or unlocking of the pll.   __

Portable FM Transmitter   -  This portable FM Transmitter is easy to build.  I have used a pair of BC548 transistors in this circuit.  Although not strictly RF transistors, they still give good range.  Transmitter is powered by 9V battery.  The coil L1 consists of 7 turns on a quarter inch plastic former with a tuning slug.  The tuning slug is adjusted to tune the transmitter.  Actual range on my prototype tuned from 70MHz to around 120MHz.  The aerial is a few inches of wire.  Lengths of antenna wire should be 1 - 2 feet.  The circuit is basically a radio frequency (RF) oscillator that operates around 70-120 MHz.  Audio from audio jack is fed into the audio amplifier stage built around the first transistor.  Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit by varying the junction capacitance of the transistor.  Junction capacitance is a function of the potential difference applied to the base of the transistor.  The tank circuit is connected in a Colpitts oscillator circuit. __

Portable FM transmitter 1 W    -  This small FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning.  All the parts are placed on one circuit board.  The RF power is switchable between 1W and 0, 2W __   Jan Kolar

Powerful AM Transmitter   -  The circuit for a powerful AM transmitter using ceramic resonator/filter of 3.587 MHz is presented here.  Resonators/filters of other frequencies such as 5.5 MHz, 7 MHz and 10.7 MHz may also be used.  Use of different frequency filters/resonators will involve corresponding variation in the value of inductor used in the tank circuit of oscillator connected at the collector of transistor T1. __

Prescaler with Counter   -  Digital frequency counter is being used for wide range of applications.  Digital frequency counter extensively uses digital circuits and hence fairly good knowledge of digital circuits and of digital integrated circuits is required to understand the operation of the frequency counter.  However a person who is not familiar with any electronics circuits and experiments has in written this article.   __

Radio Remote Control using DTMF   -  Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances.  This remote control unit has 4 channels which can be easily extended to 12.  This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals __  Designed by Radioland.net

Ramsey 25 BA1404 Stereo FM Transmitter   -  Stereo FM transmitter based on BA1404 and 145170 frequency synthesizer IC.   __

RC network quashes auxiliary winding in quasiresonant converter   -  04/01/04  EDN-Design Ideas - Quasi-square-wave-resonant converters, also known as QR (quasiresonant] converters, allow the design of flyback-type SMPSs (switch-mode power supplies] with a reduced EMI (electromagnetic-interference] signature and improved efficiency - Circuit Design  by  Nicolas Cyr, On Semiconductor, Toulouse, France

RDS Coder Board using ATmega32   -  This board is a RDS coder using an ATMEL AVR ATmega32.  This board can be controled by a RS232 link, USB interface or SPI.  TA data is displayed wiyth a LED and can be controled by :, Hardware input, RS232, USB, SPI (not yet implemented)  __

Remote control using VHF Modules   -  A few designs for remote control switches, using VG40T and VG40R remote control pair, are shown here.  The miniature transmitter module shown in Fig.1, which just measures 34 mm x 29 mm x 10 mm, can be used to operate all remote control receiver-cum-switch combinations described in this project __  Designed by Radioland.net

RF Amplifier for Ferrite Bar Antennas   -  The author described assembling this circuit on a 1"*1" perf board, I actually laid out a small PC board with excellent results.  In this era of surface mount components, I think a much smaller version can be laid out on a PC board, allowing this circuit to be put inside even the smallest radios, such as Walkmans.  If I do such a board, I will put the PC board artwork here. __  Designed by Bruce Carter

RF Buffer Stage   -  This buffer stage is intended to be used after a BF900 or BF199 (even a BF245) oscillator.  It delivers several milliwatts and is perfect to drive a 2N2219 or 2N4427.  Be sure the coils are really round and can "see" each other: place metalplates between the coils.  The supply voltage is around 12V (typ.13, 8V).   __

RF Power Meter   -  RF Power Meter for QRPers __  Designed by Peter Parker VK3YE

RF Preamplifier   -  Input needs only several mWatts (e.  g.  BF900) -> 300 mWatts OUT.  This schematic is a often used buffer.  It's easy to build, clean and cheap.  When you want even more power, you can replace the 2N2219a by a 2N4427 or 2N3553.  You can lower the output by adding a little resistor (10.47 Ohm 1/2W) in the emitter line of the 2N2219a.   __

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

 


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