The presented do-it-yourself radio bug can transmit sound at a distance of up to 500 meters. You can also use it to make an FM tuner and transmit a signal from your phone to the radio.
Radio transmitter on kt368
Do-it-yourself radio transmitter on kt368
In this article I want to talk about a radio transmitter on a single transistor.
It can be used both for wiretapping, and also make a repeater with it, replacing the microphone with an audio signal input.
DIY radio transmitter on MC2833
DIY radio transmitter on MC2833
Using the MC2833 chip, you can make a fairly high-quality FM transmitter. This microcircuit contains an oscillator, an RF amplifier, an audio amplifier and a modulator. Available in miniature plastic package with surface mount end leads and standard package.
Do-it-yourself fm transmitter for 1 km and above
DIY FM transmitter for 1 km
This is a fairly powerful 2W FM transmitter that will provide up to 10 km of range, of course, with a well-tuned full-fledged antenna and in good weather conditions, without interference. The scheme was found in the bourgeoisie and seemed interesting and original enough to be presented to your court))
Stereo radio transmitter do-it-yourself circuit
DIY stereo radio transmitter
In a car, when it is not possible to turn on music from other sources like radio, and at the same time you want to listen not to what the radio hosts provide, but to your own music, as an option, you can use the made diy FM stereo transmitter .
The radio transmitter is assembled in a standard plastic case from some kind of device. The front panel has an audio jack input and a setup button. There is a power connector on the back surface. The filter output is connected to the +12V terminal, so the power cable is used as an antenna. The printed circuit board is fixed with only one screw inside the box.
Audio transmitter
DIY audio transmitter (music transmitter)
In this article I would like to present music transmitter. I tried to assemble a radio transmitter using a varicap in the modulator. Since he was needed for the transfer sound signal, and not a conversation, put a plug instead of a microphone. Coil 9 turns of wire with a diameter of 1 mm, the middle tap is soldered. I shoved a small piece of foam rubber inside the coil and dripped it with paraffin (candle) so that the coil would not bend when touched, because the frequency depends on it, and it is very easy to knock it down.
Do-it-yourself stereo transmitter circuit
Radio stereo sound transmitter circuit
For stereo transmitters, there is ASIC, BA1404.Ofeature transmitter on BA1404 is high sound quality and improved stereo sound separation. This is achieved by using a 38 kHz crystal that provides the pilot tone frequency for the stereo encoder.
A stereo transmitter can be used both at home and in a car to transmit sound from a carrier (phone, player, etc.), since it does not transmit stereo sound.
Such a small stereo transmitter will be a good replacement for an FM tuner.
DIY FM transmitter
FM radio transmitter
Do-it-yourself VHF-FM radio transmitter operates in the non-traditional range of 175-190 MHz. These radio microphones are easy to assemble. In order to increase the frequency stability of the master oscillator, the base circuit of the power amplifier transistor is powered by a voltage regulator (R5, LED1).
Used SMD RED Light-emitting diode. The frequency deviation during the “drawdown” of the power supply from 3 to 2.2 volts is no more than 100 kHz. When you touch the antenna with your hand, the frequency deviates slightly too. If you have a receiver with a good AFC, it tracks this change and the frequency drift does not occur at all during the operation of the transmitter.
Powerful radio transmitter for 500 meters with your own hands
Do-it-yourself radio microphone for 500 meters
I want to present the design enough powerful radio bug, Range which is up to 500 meters with line of sight. The device was assembled almost a year ago for our own needs. beetle revealed amazing results: The frequency almost does not float (only 0.1-0.3 MHz every 100 meters). The device does not respond to the touch of the antenna and other parts (except for the circuit and the frequency setting circuit) - this is very important point, since almost all schemes from the Internet have such a problem.
In the practice of creating radio bugs, we often encounter the problem of the smallest possible size of a bug. Today we will talk about just such a bug: NEMESIS-2, as it was called. Nemesis was assembled on smd components, due to which it became possible in a significant way downsize bug several times, the radio bug is so small that it fits, for example, in one cigarette, lighter or mobile phone. A little about the parameters: the frequency range within 88-108 megahertz, microphone sensitivity about 5 meters, ticking is heard in a quiet room wall clock. So this signal is easy to receive from this bug to the radio, whether it is in the phone, or just stationary. Let's move on to the diagram and details.
If you need to transmit audio sound over a relatively short distance, then you can assemble the circuit presented on this page. The circuit is based on two NPN transistors. BC547. The range at best will be 70 meters. You can adjust the sound transmission volume using variable resistor at 100 kiloOhm, as well as on the receiver itself. An LED with a 330 ohm resistor is optional, it serves as an indicator.
Schematic diagram of a simple transmitter
I used this device for broadcasting sound so that I could listen to the music I needed while on short distance from home, for example in a garage, and receive a signal on an ordinary FM radio. There is a lay format printed circuit board - download.
An analogue of imported silicon bipolar npn transistor bc547 is domestic kt3102. The higher the gain of the transistors, the more powerful the audio transmitter will be. If you want to make the device miniature, use transistors in the sot-23 package: BC847. The picture below shows the location of the base, collector and emitter.
The best, in my opinion, power for the circuit will be two batteries AA 1.5 V connected in series. Together they will give a voltage of three volts. The operating time depends on the current consumption, as well as on the capacity of the batteries. Usually the higher their cost, the better they are. For example, if you use fairly expensive batteries GP Ultra Alkaline, with a capacity declared by the manufacturer of 3.1 A at a current in the circuit of 8 mA this device will be able to work without interruption, roughly speaking 387 hours. The problem is that it is very difficult to “suck out” the entire charge of the battery. Therefore, in reality, the circuit will work without turning off and with stable signal transmission for approximately 150 hours, or almost 7 days.
The coil has six turns of insulated copper wire with a cross section of 0.3-0.5 mm. We wind this coil on the paste from the handle.
When testing the device, the current in the circuit was almost 10 mA.
It is very easy to catch the frequency of the transmitter by twisting the subscript capacitor and “playing” with the coil, shifting and pushing its turns. I "caught" my transceiver at a frequency of 89.90 MHz.
I assembled this circuit on smd parts, only I took transistors in the TO92 package. The antenna is a piece of copper wire, the more the better. If you just touch the antenna wire, then the frequency does not go away, and if you pick it up, noise starts in the receiver's headphones.
I tried to transmit sound both from a computer and from a phone. A signal that is too loud is transmitted with numerous noises and wheezing, the optimal sound strength is adjusted by a trimmer resistor. In general, the audio quality is quite good. Taken in black and white Nokia phone and listened to the sound through headphones. There were no major problems with acceptance.
Video of the sound transmitter below. Song: bwb - my boys.
Transmitter operation video
On this I apologize. was with you EGOR .
Discuss the article HOME-MADE FM TRANSMITTER
Today I want to bring to your attention the easiest, simplest and cheapest FM transmitter kit.
Description:
This project is an instruction for making the simplest single transistor FM transmitter.
You can make this device using a small number of components. This project is for beginners.
Please review the diagram below before proceeding. The diagram shows the components needed to make an FM transmitter. The range of the device, according to this scheme, is approximately 10-20 meters.
The FM transmitter circuit looks like this: 
For this experiment the following components are required:
1. Q1- Transistor- 2N3904 
2. Capacitors - 4.7pF, 20pF, 0.001uF, 22nF.
Note: 0.001uF is code 102 and 22nF is code 223.
3. Variable capacitor: VC1. It is also called a trimmer capacitor. You can buy it at your local radio store. The adjustable capacitance range is 0-100pF or 10-100pF. If there is no such capacitor, then a tuning capacitor with a minimum capacitance of 20 pF can be used. This capacitor can still be removed from a broken radio, but this may require assistance.
4. Resistors - 4.7 kOhm, 470 Ohm
5. Condenser / electret microphone 
On the electret microphone one of the terminals has a lamella connected to the microphone body. Remember that this conclusion is always negative.
6. Inductor - 0.1 uH.
6-7 turns with 26 SWG (0.455 mm) wire.
You need to strip the ends of the coil. Otherwise, it won't work. 
You can also use another coil. 
7. Antenna: Use a long wire between 15 cm and 1 meter for the antenna. The longer the antenna, the better the signal transmission will be.
The following figures show the manufacturing process of the FM transmitter. Just follow the steps exactly.
You can see in the picture below that I didn't use the trimmer/ variable capacitor. I used a 20pF fixed capacitor instead. So if you couldn't find a variable capacitor, you can also use a fixed capacitor. 
Mount the transistor, resistors, and capacitors on the breadboard. The component ratings are shown in the previous figure. 
Next, insert an electret microphone.
NOTE: body-related output is -ve 
Use a 15 cm long antenna. You can use a regular wire as an antenna. 
After that, with a non-conductive tool, adjust the capacitance for the cleanest reception, turn the knob until the receiver picks up sound from the transmitter's microphone. Use the following formula to determine the frequency.
Tune the FM receiver to a free station.
Good luck!
Hello, friends. With this transmitter, you can easily transmit a stereo signal from a smartphone to a car radio with an FM receiver. This stereo transmitter is very easy to manufacture, it is built on a single specialized BA1404 chip. This chip already includes a stereo amplifier audio frequency, multiplexer, subcarrier frequency generator, carrier frequency generator, radio frequency amplifier. The supply voltage of this microcircuit is 1-2V, current consumption is up to 5 mA. Coils L1 and L2 are wound with PEV-2 wire with a diameter of 0.5 mm. on a mandrel with a diameter of 3 mm. and contain 4 turns. The device diagram is shown in Figure 1.
Figure 1- BA1404 Stereo Transmitter Schematic Diagram
The device is assembled on a single-sided fiberglass 35x50 mm in size. The printed circuit board is shown in Figure 2.
Figure 2 - printed circuit board stereo amplifier chip BA1404
Radio elements and analogues
Transistor VT1 KT368 can be used with any letter index, transistor KT399 is also suitable
Trimmer capacitor C14 - CTC-05-10RA, ceramic capacitors K10-17 or similar imported ones, for example CL0805.
Resistors are ordinary MLT or similar imported ones.
Setting up and configuring the device
First of all, the transmitter should be tuned to a frequency free from radio stations. Remember that interference with radio stations is punishable. I advise you to read the Federal Law on Communications No. 126-FZ of 07.07.2003. The circuit C13, C14 and L1 is responsible for the operation of the transmitter at a certain frequency. By adjusting the capacitor C14 and increasing or decreasing the distance between the turns of the coil L1, the transmitter can be operated at the frequency we need. Circuit C20, C21 and L2 are responsible for matching the device with the antenna. To adjust the matching, you can use the field strength indicator, if it is not there, then the receiver should be moved away and tuned by ear, by increasing or decreasing the distance between the turns of the L2 coil. It is desirable to use an antenna with a length equal to a quarter wavelength. Antennas can also be used smaller, but the communication range will decrease.
Bibliography
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