Any source of magnetism, such as a magnet or electromagnet, is surrounded by a magnetic field.
When you bring a compass near an item suspected of being magnetized or having a magnetic field, the compass will turn and point toward the appropriate pole of the object. A famous experiment showed that a wire with DC electric current running through it created a magnetic field.
By spreading fine iron filings or dust on a piece of paper laid on top of a magnet, you can see the outline of the magnetic lines of force or the magnetic field.
These devices are used to detect and measure magnetic fields in scientific experiments, in industry and even in people's homes.
Please include it as a link on your website or as a reference in your report, document, or thesis.
This easy to build transmitter transmits high quality stereo sound from your MP3 player, computer, walkman or discman to any FM radio or car radio. FM transmitters can be complicated to build, but not this one — this iPod FM transmitter about the easiest you can possibly make. This simple circuit is based on BA1404 FM Transmitter, works with two AA batteries and can drive a 300W dipole antenna for improved range. This 7 Watt FM Transmitter was originally a 200mW unit, without the universal power stage added. FM transmitters can be complicated to build, but not this one it’s about the easiest you can possibly make. 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.
Presented FM transmitter is built around low power PLL transmitter and amplifier that boosts its signal all the way up to 6 Watts.
If you are looking for an easy or simple FM transmitter circuit in which you don't have to make a coil with your hand then the circuit given here is ideal for you. This small phone transmitter will transmit a phone conversation to an FM radio on the 88-108MHz band.
This classic walkie talkie consists of both 27MHz transmitter and receiver all in one circuit. This is a 1 Watt FM Transmitter amplifier with a good design that can be used to amplify a RF signal in the 88 – 108 MHz band.
Here is a very interesting and simple FM transmitter used to transmit audio in the wide range up to 100M using only one transistor. A simple MP3 FM transmitter circuit shown here can be built easily in few minutes if all parts are available to you.
This low power fm transmitter is designed to use an input from another sound source and transmits on the commercial FM band. This article shows you how to build a very simple FM transmitter from thirteen components, a Printed Circuit Board (PCB) and a 9v battery. Long range, very stable, harmonic free, FM transmitter circuit which can be used for FM frequencies between 88 and 108 MHz.
This design is more or less broadband however I added two variable capacitors after each stage for optimum matching and power output. For months I’ve been looking for a simple FM BUG project, the ones online require inductors which you either have to acquire or build, if you don’t have a LCR meter it becomes rather hard to get the circuit working, specially if you’re a beginner without an oscilloscope! 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 little broadcast FM transmitter has 500mW of RF output power and runs of 12-15V battery or power supply.
There are many miniature FM transmitter bug circuits online, this one is unique in that it runs completely on solar power. The power output of many transmitter circuits are very low because no power amplifier stages are incorporated.
Here is a simple USB FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio by connecting it to an USB port. 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.
Normally these designs have only two transistors: one is the X-tal oscillator and the second the final amplifier. When conditions are normal, you can easily make many QSO's during one afternoon with stations with distances upto 2000 km with a simple inverted V wire dipole antenna! This PLL transmitter is controlled and the frequency is very stable and can be programmed digitally. 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. 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.
The first stage of transmitter is a mic amplifier but if you connect this radio transmitter directly to an audio source you can remove this stage and connect the audio signal to R5. With this circuit you can build a very small tracking transmitter that can be tracked using a FM broadcast band radio receiver. The objective of this 1.5V FM Broadcast Transmitter design is to provide a simple low-power transmitter solution for broadcasting audio from various audio sources. This FM Broadcast Transmitter circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Here is a very simple telephone broadcaster transmitter which can be used to eavesdrop on a telephone conversation.
One important feature of this phone transmitter is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies.
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'll see that you can receive the signal through the air with almost any AM radio receiver. A wide range of different circuits have been used for AM, but one of the simplest circuits uses collector modulation applied via (for example) a transformer, while it is perfectly possible to create good designs using solid-state electronics as I applied here (T1 BC557). With this Stereo FM Transmitter with BA1404 you will be able to create a mini stereo FM station and broadcast to your entire home, a simple way to have an audio link wireless with ease. That field can be detected by various devices, which can also give information about the direction of the field and even its strength. When the electricity was turned on, a nearby compass moved to indicate a magnetic field was present. The North-seeking pole of the compass needle will always point toward the Earth's North magnetic pole.
They use a electronic chip called a Hall effect device, which gives off a tiny electrical current when exposed to a magnetic field.
Devices can detected the field and also give information about the direction of the field and even its strength. It utilities a variable high gain audio pre-amplifier which can detect voices 40 feet away using an electret microphone. And though the science of radio is well understood, there’s a magical, emotional quality about it that we don’t often stop to appreciate.
It is basically a VHF Colpitts oscillator capable of transmitting sound or music to any standard FM receiver.
There are many applications for an FM transmitter, particularly if it can broadcast in stereo. Output can be tuned from 88 to 108Mhz and the transmitter can be battery powered or be used with presented low voltage power supply. The circuit is using a ready made 1uH inductor which can be purchased from an electronic components store. It transmits FM waves so you could easily receive the signals on your mobile phone, radios, etc. Nearly all the components in the 4-transistor circuit are used for both transmitting and receiving making it simple to build and economical at the same time. 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.
Veronica is also known for frequency stability, clean FM signal and uses no integrated circuit. Transmitter uses a PLL frequency synthesizer built with MC145152 which covers the FM band in 100kHz steps. The entire circuit of FM transmitter is divided into three major stages oscillator, modulator and amplifier. The RF output varies from 500mW to about 1.2W depending on the frequency selected and RF output transistor used. You could construct the project on Vero board (strip board) or any other 0.1” pitch style of project board. The amplifier has two stages using BLF244 mosfet transistor for the first stage which requires 0.5 - 1Watt of RF input to get about 20watts to drive the final stage SD1407 which can push nearly 200 Watts on this design.

Make sure the trimmer and the capacitors after the final stage SD1407 are a high voltage types with at least 200V rating.
VC1 is a small, screw-adjustable, trimmer capacitor and its rating should be around 10-100pF.
This fun project will show you how to build a mini broadcasting transmitter that can transmit an audio signal up to a quarter mile to any FM receiver.
The transmitter circuit described here has an extra RF power amplifier stage using 2N3866 RF power transistor after the oscillator stage to increase output power to 250 milliwatts. Operating voltage range is 1-3V, the circuit contains FM stereo mixer, 38KHZ oscillator, FM modulator and high-frequency amplifier monolithic integrated circuit. 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.
This is a nice QRP transmitter that can be used in combination of one of the simple receivers. You must use a stabilized power source for oscillator stage to prevent frequency variation.
Its low-frequency signal is converted into high-frequency, which can take any audio device with FM radio (stereo, car CD, MP3, DVD player, etc.), as a normal radio station. This particular TX is of special interest to those wishing to build low power Power Amplifiers for the VHF bands since it used impedance matching, power amplifier and antenna filtering, all of which should be used by radio constructors, whether it be for amateur radio or any other form of radio.
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.
It works quite easy, there is a power switch on the bottom to turn it on and tune your radio and transmitter to the right frequency. With the FM transmitter BA1404 Hifi Stereo you can stream your music from your iPod MP3, satellite receiver, computer, DVD player, Mobile Phone, MP4 player and MP3 and other audio source directly to an FM receiver with crystal clear sound. At the sophisticated level, a gaussmeter can detect a field and indicate its strength, as measured in gauss units. The current is amplified with electronic circuitry and a meter shows the number of gauss (the units of magnetic field strength). The IC requires only a small number of external parts so it is well suited for hobbyist projects. You will not forget the first time you pick up a transmission broadcast from a device you soldered together, yourself, from a few bits of copper, carbon, plastic, and wire.
You can broadcast stereo signals from your CD player or any other source to an FM tuner or radio. I used this transmitter with a half-wave open-end dipole in a vertical position 50 feet above ground. This runs at very low voltage, by a CR2025 3V battery, current consumption is also low.And the total size of this FM transmitter (including battery, excluding antenna) is less than that of a matchbox. In the first and second stages of the transmitter one of the best driver transistors were used 2SC2053.
As the name and the picture indicates it is very small and is approximately the size of a 9v battery clip.
The frequency-generating stage only needs 27MHz crystal to be removed and it becomes a receiver. The Veronica oscillator is actually formed from 2 oscillators which operates somewhere around 50 MHz in anti phase and the 2 signals are combined to form 100MHz FM radio signal. The VCO uses MV2109 varicap diode to automatically tune to selected frequency via SW1 dip switch. You can build simple FM transmitter with one BC549 transistor and several other component parts.
The circuit will work as a best FM transmitter for simply broadcasting your music around your house and yard, and can be used to broadcast the output of any equipment like mp3 player, ipod, satellite, etc. It is the responsibility of the builder to check the legal requirements for the operation of this circuit and to obey them. The oscillator is a colpitt stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor. If you just want to experiment with this circuit, you don’t even need a board; you can just solder the component s together and let the completed project just rest on the work top.
It has a very stable oscillator because it uses LM7809 voltage regulator which is a 9V stabilized power supply for T1 transistor. The power on this amplifier can be varied by adjusting the bias voltage using the white pot to the BLF244 mosfet. This circuit on the other hand performs pretty well, even if you’re manipulating the board or touching the coax it will stay within the tuned frequency (unless you touch the transistor or timing capacitor!). Transmitter's frequency, as built is tunable via 15pF trimmer to the desired frequency, and the coil is embedded on the circuit board. With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometers.
As the "electronic newspaper" BBS there are many users requiring detailed information on the FM stereo transmitter, so I re-collect the relevant information on the simple discrete, merge, integrated FM stereo transmitter experiment, that BA1404 with μpc1651 mix of the most easy to make and debug, and very high frequency stability (relative to the previous circuit BA1404), transmission power is increased by UPC1651RF amplifier.
BA1404 is a monolithic FM stereo modulator that has built in stereo modulator, FM modulator, RF amplifier circuitry. You can remove C7 and use a linear potentiometer instead of R6 with the median connector to C4, one pin to ground and the other one to +. Transmitter has a range up to 1 mile depending on battery voltage, height above ground, receiver sensitivity, and antenna length. Transmitter power is sufficient for reliable reception of its signal within a few tens of meters. Since there is no audio level control on the input, the audio level out from the source needs to be adjusted. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. The chip features excellent frequency stability, low power consumption & good channel separation. Transmitter should be powered by regulated 12-14V power supply with at least 100mA current rating. The circuit also does not require a trimmer capacitor, because we have used a fixed value of 39pF capacitor in the place of trimmer capacitor. The circuit should be built on an epoxy printed circuit board with the upper face components reserved for interconnecting tracks and the bottom solder to the ground plane.
The input audio generated by microphone is changed into electric signal and is given to base of transistor T1. 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 diagram shows a 2N3375 driving a 2N5643 but there are many other transistors that will work. I added a zener diode onto the bias supply to protect the transistor from too much bias voltage. Then, with a non-conductive tool, adjust the capacitor for the clearest reception, rotate it till the receiver receives a sound from the microphone of transmitter.
This implementation is adapted to rebroadcast the output of a CD player, television receiver, or radio receiver. Using the values of the circuit components, the frequency will be around 100 MHz but can be changed via coil. The transmitter bug is useful as a "remote ear", and can be used for anything from listening birds to surveillance work. BA1404 FM transmitter can be operated from 76 to 108MHz and power supply for the circuit can be anything between 1.25 to 3 volts. To keep the fm transmitter circuit simple as well as compact, it was decided to use a chip made by Maxim Integrated Products, the MAX2606. This VXO is buffered with an extra driver stage for a better frequency stability and a varicap diode is used instead of a variabele capacitor.
A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency.
The output frequency can be easily adjusted by potentiometer thanks to onboard MV2109 varicap diode and the frequency stability is quite good. It broadcasts on the FM band (88-108MHz) so that it can be received by any standard FM tuner or portable radio. You can experiment with the size of the coil and the number of turns to see how it affects the frequency and signal output of the oscillator. The IC can be driven from a 7805 Regulator with a couple of 1N4001 diodes to reduce the supply voltage to about 2.8 Volts.
We have already calculated and used the values of coil and capacitors of oscillator to broadcast on FM band, so you don't have to do any further adjustments and tuning after building the circuit. The first transistor is a pre-amplifier and the next two are wired as a super-alpha pair, commonly called a Darlington pair to drive the speaker that is also used as a microphone. Veronica transmitter is equipped with a mini-mixer and so you may forget an external mixer.

The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage. I use this transmitter so that I can move about the house and listen to my favorite programs without disturbing others. Through the 5 pF capacitor and 10K ohm resistor, the modulation of audio signal is supplied to the tank circuit. The mic preamp and oscillator circuits were borrowed from a common circuit found around the Internet, a regulated solar power supply and an RF amp that extends the range of transmitter and improves frequency stability were added. Having a range of up to a quarter mile, it's great for a house security system, baby monitoring device or simply a listening gadget that you can place anywhere! On the computer I had to reduce sound to about 35% of capacity, so that I do not have clipping.
This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. You can power the fm transmitter bug with a 9Volt Battery, or you can plug a power supply to feed in 9-12 Volts.
It is recommended that this transmitter be used with FM radios that can tune continuously across the dial. This device contains all the necessary circuitry to generate a composite stereo signal c of the pilot tone, the RF generator with PLL and power amplifier. Transmitter's frequency, as built is tunable via spreading or compressing the coil to the desired frequency, and the coil can be glued down. Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. This 2 turn coils is paired with a 39 pF capacitor (Cx) to give a frequency range from 87 MHz - 106 MHz. 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.
I eliminated the tuning capacitor, which is usual for most bugs and miniature transmitters, because this greatly complicates the tuning. RF output power is typically 500mW but range depends upon antenna coupling and efficiency, environment and size of antenna. 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. It uses "frequency modulation" most commonly known as FM, the same principal to transmit audio signals captured by the microphone. BB110 variable capacitor connected to the collector of transistor BF199 adjusts the transmission frequency of the circuit. This consist from T1 transistor which amplifies the microphone signal before it is combined with cd-player audio or PC signal. Transmitter may be built on a double sided PCB, with top side copper left mostly undisturbed as a ground plane. If any of the variable capacitors are at full capacitance you can pad them out with a fixed ceramic capacitor of suitable value. 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. The amount of modulation is being managed by the 1N4002, a general purpose rectifier diode.
A varicap diode circuit is included to tune the frequency of the transmitter and to provide frequency modulation by audio signals. That bug will pick even a low whisper or even the sound of a breath well far from the microphone.
The signal varies the capacitance of the varicap and hence varies the oscillator frequency which produce Frequency Modulation.
The better the receiver and receiver antenna system the greater the practical range of the transmitter, however good functionality can be achieved with the least expensive radios and using only the standard telescoping antenna included with most radios. If you want to make one that's tunable, it might be easiest to reduce the 18 pf capacitor and put a small trimmer capacitor in parallel with the inductor (across the reduced value capacitor). You could also add a LF preamp stage of one transistor to allow connecting a dynamic microphone directly. From my own experience I know that if you get closer to such capacitor, the operating frequency is changed. For antenna use a 12 inch wire or for maximum range use a 30 inch wire and make it vertical.
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). FM Transmitter's output stage is functioning as a class D amplifier where the output transistors act as a switch. The variable-capacitance (varicap) diode and feedback capacitors for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency.
Voltage variable capacitors would be an nice alternative to a mechanical variable capacitor but they don't offer much tuning range with only a 1.5V power supply.
It is ideal to tune up this circuit using a wave detector meter placed a few inches away from the transmitter. Of course, one would be better off with more equipment than I have had to capture the main oscillating frequency.
By using a standard TV antenna, the range of this transmitter can go up to 1KM radius, using small 15-20cm wire, it can work up to around 50M range.
That's why I chose to use the voltage tuning using the Voltage Controlled Oscillator (VCO).
Once the output frequency is adjusted amplifier variable capacitors must be adjusted for maximum output power one stage at a time. The ground connections can be soldered on the top side, so it’s not necessary to have plated-through holes. The transistors are bolted to a piece of right angle aluminum which is fixed to the metal chassis to dissipate heat effectively.
Oscillator is a VCO (voltage controlled oscillator) which is set by the PLL circuit and PIC micro controller.
The oscillator signal is taken from the collector of T2 and guided to the input of T3 which output is lead via an L-filter and low-pass PII filter circuit cleaning up the signal pretty good and ensuring spectral purity. This circuit is most suitable for miniature FM transmitter for use in computer, mobile etc to send music to home theater system without wires, and in homemade wireless walky-talkies. Instead of tuning capacitor the varicap (capacitance diode) is used, which changes its capacity by changing the reverse DC voltage.
All adjustments must be made with 50 Ohm dummy load connected to the output of transmitter. This oscillator is called the Colpitts oscillator and voltage controlled to achieve the FM (frequency modulation) and PLL control. It was thru trial and error, with the FM tuner, in finally finding out how to grab the right frequency. The transistor gives a RF humming accordingly to the audio input, and the FM wave is spread by the external antenna. The circuit is basically a radio frequency (RF) oscillator that operates around 70-120 MHz.
By keying the morse-key T1 is not been used for modulation and is biased, hence lets T2 freely oscillate.
When I finally did get used to find out where my 'main' frequency was, the unit performed extremely well.
By using a standard TV antenna, the range of this transmitter can go up to 1KM radius, using small (15-20cm) Ariel, it can work up to around 50M range.
Audio from audio jack is fed into the audio amplifier stage built around the first transistor. 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. 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. 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.
Junction capacitance is a function of the potential difference applied to the base of the transistor. When I got to the top of the overpass in my car, the audio signal came in as 'clear as a bell'.
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.

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