The presented radio bug with its own hands can transmit sound over 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 for KT368

DIY radio transmitter for KT368

In this article I want to talk about a radio transmitter using a single transistor.

It can be used both for wiretapping, and you can also use it to make a repeater, 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 chip contains an oscillator, an RF amplifier, an audio amplifier and a modulator. Available in miniature versions plastic case with surface mount terminals and standard housing.

DIY FM transmitter for 1 km and above

DIY FM transmitter for 1 km

This is a fairly powerful 2 W FM transmitter that will provide up to 10 km of range, naturally with a well-tuned full antenna and in good weather conditions, without interference. The scheme was found in the burzhunet and seemed interesting and original enough to be presented to your consideration))

DIY stereo radio transmitter circuit

DIY stereo radio transmitter

In a car, when it is not possible to turn on music from other sources like the radio, and at the same time you want to listen not only to what the radio presenters provide, but to your own music, as an option you can use the one made DIY FM stereo transmitter .

The radio transmitter is assembled in a standard plastic case from some 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 PCB is secured with only one screw inside the box.

Audio transmitter

DIY audio transmitter (music transmitter)

In this article I want to introduce music transmitter. I tried to assemble a radio transmitter using a varicap in the modulator. Since he was needed for transmission sound signal, and not a conversation, I put a plug instead of a microphone. Coil of 9 turns of wire with a diameter of 1 mm, the middle tap is sealed. I pushed a small piece of foam rubber inside the coil and dripped it with paraffin (a candle) so that the coil would not bend when touched, because the frequency depends on this, and it is very easy to knock it down.

DIY stereo transmitter circuit diagram

Radio stereo audio transmitter circuit

For stereo transmitters there is specialized chip BA1404.ABOUTfeature transmitter on BA1404 is high quality sound and improved stereo sound separation. This is achieved by using a 38 kHz crystal oscillator, which 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 storage device (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. This radio microphone is easy to assemble. In order to increase the frequency stability of the master oscillator, the base circuit of the power amplifier transistor is powered from a voltage stabilizer (R5, LED1).

Used SMD RED LED. The frequency shift when the power drops from 3 to 2.2 volts is no more than 100 KHz. When you touch the antenna with your hand, the frequency also deviates slightly. If you have a receiver with a good AFC, it tracks this change and the frequency shift does not occur at all during the operation of the transmitter.

Do-it-yourself powerful radio transmitter for 500 meters

DIY radio microphone for 500 meters

I want to present the design enough powerful radio bug, Range which amounts to 500 meters with line of sight. The device was assembled almost a year ago for my own needs. Beetle showed amazing results: The frequency hardly fluctuates (every 100 meters by only 0.1-0.3 MHz). The device does not respond to touches of the antenna and other parts (except for the circuit and the frequency-setting circuit) - this is a very important point, since almost all circuits from the Internet have such a problem.

In the practice of creating radio bugs, we often encounter the problem of the minimum possible size of a bug. Today we will talk about just such a bug: NEMESIS-2, as it was named. 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 will fit, for example, in one cigarette, lighter or mobile phone. A little about the parameters: frequency range within 88-108 megahertz, microphone sensitivity about 5 meters, in a quiet room you can hear the ticking of the wall clock. So this signal is easy to receive from this bug to the radio receiver, whether it’s on a phone or just a landline one. Let’s move on to the diagram and details.

A microphone amplifier based on elements T1 and T2 amplifies the signal from the electret microphone VM1 to a level that provides a given frequency deviation. The transistors are connected according to a common emitter circuit and feedback by voltage.

The capacitance of capacitors C2 and C4 is not standard, but smaller than usual, which raises the high frequencies of the audio signal and increases speech intelligibility.

We set the required deviation, and therefore the volume, by adjusting resistor R2.
From the engine of the construction resistor R2, the amplified signal is supplied to the second amplification stage. From the second stage, the signal is fed to a varicap, which performs FM modulation of the signal. A miniature high-quality varicap from TV tuners is used as a varicap. Frequency modulation is produced by changing the capacitance in the quartz circuit depending on the voltage applied to it. At rest, the varicap is supplied with half the supply voltage. Quartz resonator is excited in the master oscillator at the fundamental frequency of 13.56 MHz.

From the emitter of transistor T3, a frequency-modulated signal with a swing almost equal to the supply voltage is supplied to the multiplier T4. Circuit L2, C9 is tuned to a frequency of 94.92 MHz, highlighting the seventh harmonic of the master oscillator. Through capacitor C10, HF oscillations from the circuit are transmitted to the antenna.

This scheme master oscillator has certain advantages. Even low-active quartz works stably in it. A large difference in the frequencies of the master oscillator and the multiplier reduces the influence of radiation from the output circuit on the operation of the generator.

Quartz - at 13.56 MHz in a metal case. Frequencies may differ, but the 7th harmonic must fall in the FM range on a free frequency.

Coil L2 is wound with 0.6 mm silver wire on a mandrel with a diameter of 3 mm and contains 10 turns with a tap from the middle. Chokes L1 - SMD. Capacitors are ceramic SMD. The antenna is a piece of wire 0.5 meters.

The radio microphone is made on two-way printed circuit board. The second solid side is a common wire and at the same time a screen. In the marked places, the layers are connected by jumpers. At the connection points of the output components, part of the foil of the second layer is removed with a drill. After completing the setup, the entire structure can be filled with sealant or polyethylene glue.

Settings
Initially it starts with a microphone amplifier. Current consumption and voltage are set by the values ​​of resistors R3, R5. High-impedance telephones control the passage of the sound signal to collector C2.

An RF probe or oscilloscope is used to check the operation of the master oscillator at the connection point of capacitors C6, C7, C8. Generator current consumption is 2...3 mA.

Circuit L2, C9 is tuned to resonance by shifting and spreading the turns of coil L2 and adjusting C9. The final adjustment of the circuit can be carried out based on the operating range of the radio microphone. By selecting resistor R10, the current consumed by the multiplier is set to about 10...15 mA.

Complete the setup by setting resistor R2 to the required volume. It should be expected that it will be slightly lower than the volume of FM stations, since the deviation is only 21 kHz instead of 75 kHz.

Schematic diagram

The use of superheterodyne receivers, the bandwidth of which can be narrowed down to the value of the active spectrum width of the received signal, can significantly increase the noise immunity of receivers and their sensitivity. As a result, the operating range of the equipment increases without increasing the transmitter power.

However, superheterodyne receivers, the bandwidth of which does not exceed 10-12 kHz, require such high stability of the transmitters that the shifts in the emitted frequency will not exceed 5-10% of the bandwidth. In absolute terms, this is 0.5-1.2 kHz. Consequently, the relative instability of transmitters in the range of 27-28 MHz should not exceed 1.8-10"5. Such high requirements can only be met by quartz-stabilized generators.

It was already noted above that it is impractical to carry out modulation in the master oscillator itself, so the transmitters are at least two-stage. In Fig. Figure 3.24 shows a diagram of such a transmitter in which quartz ZQ1 operates at the third mechanical harmonic. The resonator is connected between the collector and the base of the transistor, which, as practice shows, allows you to combine the simplicity of the circuit with high reliability of its operation even with quartz having low activity. The output power of the transmitter does not exceed 10 mW.

It must be borne in mind that quartz operating at the first harmonic is mainly produced up to 20 MHz. Since the resonant frequency depends on geometric dimensions quartz plates, then at higher frequencies the dimensions are so small that it is technologically difficult to produce a plate with three

expected characteristics. For this reason, if a frequency of more than 20 MHz is applied to the quartz body, then this quartz is most likely harmonic.

Since opposite potentials must be induced on opposite faces of the plate (due to the piezoelectric effect), excitation is possible only at odd harmonics, usually no higher than the seventh. To prevent such quartz from being excited at the fundamental frequency, the circuit must have a circuit tuned to the required harmonic. In the circuit under consideration, this circuit consists of inductance L1 and capacitor C2.

A power amplifier operating in class B mode is implemented on transistor VT2 due to the absence of a constant bias at the base of the transistor. The emitter circuit of this transistor is switched by an electronic switch VT2, controlled by base modulating pulses from the output of the encoder. The antenna is connected to the output circuit through extension coil L3. Partial switching is used through a capacitive divider C6C7, providing a matching mode.

Details and design

The printed circuit board is shown in Fig. 3.25. The ZQ1 quartz resonator is used at a frequency of 27.12 MHz. You can also use the fairly common ones at 27.14 MHz. Coil L1 consists of 24 turns of wire with a diameter of 0.12-0.15, wound on an MLT-0.5 resistor with a resistance of at least 100 kOhm. L2 is wound on a frame with a diameter of 6 mm with a tuning core made of carbonyl iron and has 9 turns of wire with a diameter of 0.5 mm.

Extension coil L3 is a standard 5 µH DM inductor (PDM). All transistors can have any letter index; replacement with KT3102 is also possible.

Ceramic capacitors, type KM-5, KM-6 or similar. Whip antenna, 40-60 cm long.

Settings

The setting comes down to installing core L2 in a position that ensures the maximum amplitude of output oscillations. The pre-modulation input is connected to the positive side of the power supply. The amplitude is monitored using an oscilloscope as described in the previous paragraphs. Between the VT1 base and the case, the diagram shows a capacitor in dotted lines (there is a place for it on the board). If the generator does not self-excite (due to low quartz activity), you need to solder a capacitor in this place, selecting it in the range of 120-180 pF for the maximum output oscillations. In the absence of the specified quartz, you can try to install the resonators at a frequency three times lower than the required one (9.04-9.046). The transmitter operates reliably when the supply voltage is reduced to 5 V.

Schematic diagram

The use of superheterodyne receivers, the bandwidth of which can be narrowed down to the value of the active spectrum width of the received signal, can significantly increase the noise immunity of receivers and their sensitivity. As a result, the operating range of the equipment increases without increasing the transmitter power.

However, superheterodyne receivers, the bandwidth of which does not exceed 10-12 kHz, require such high stability of the transmitters that the deviations of the emitted frequency will not exceed 5-10% of the bandwidth. In absolute terms, this is 0.5-1.2 kHz. Consequently, the relative instability of transmitters in the range of 27-28 MHz should not exceed 1.8-10″5. Such high requirements can only be met by quartz stabilized generators.

It was already noted above that it is impractical to carry out modulation in the master oscillator itself, so the transmitters are at least two-stage. In Fig. Figure 3.24 shows a diagram of such a transmitter in which quartz ZQ1 operates at the third mechanical harmonic. The resonator is connected between the collector and the base of the transistor, which, as practice shows, allows you to combine the simplicity of the circuit with high reliability of its operation even with quartz having low activity. The output power of the transmitter does not exceed 10 mW.

It must be borne in mind that quartz operating at the first harmonic is mainly produced up to 20 MHz. Since the resonant frequency depends on the geometric dimensions of the quartz plate, at higher frequencies the dimensions are so small that it is technologically difficult to produce a plate with three

expected characteristics. For this reason, if a frequency of more than 20 MHz is applied to the quartz body, then this quartz is most likely harmonic.

Since opposite potentials must be induced on opposite faces of the plate (due to the piezoelectric effect), excitation is possible only at odd harmonics, usually no higher than the seventh. To prevent such quartz from being excited at the fundamental frequency, the circuit must have a circuit tuned to the required harmonic. In the circuit under consideration, this circuit consists of inductance L1 and capacitor C2.

A power amplifier operating in class B mode is implemented on transistor VT2 due to the absence of a constant bias at the base of the transistor. The emitter circuit of this transistor is switched by an electronic switch VT2, controlled by base modulating pulses from the output of the encoder. The antenna is connected to the output circuit through extension coil L3. Partial switching is used through a capacitive divider C6C7, providing a matching mode.

Details and design

The printed circuit board is shown in Fig. 3.25. The ZQ1 quartz resonator is used at a frequency of 27.12 MHz. You can also use the fairly common ones at 27.14 MHz. Coil L1 consists of 24 turns of wire with a diameter of 0.12-0.15, wound on an MJIT-0.5 resistor with a resistance of at least 100 kOhm. L2 is wound on a frame with a diameter of 6 mm with a tuning core made of carbonyl iron and has 9 turns of wire with a diameter of 0.5 mm.

Extension coil L3 is a standard 5 µH DM inductor (PDM). All transistors can have any letter index; replacement with KT3102 is also possible.

Ceramic capacitors, type KM-5, KM-6 or similar. The antenna is whip, 40-60 cm long.

Settings

The setting comes down to installing core L2 in a position that ensures the maximum amplitude of output oscillations. The pre-modulation input is connected to the positive side of the power supply. The amplitude is monitored using an oscilloscope as described in the previous paragraphs. Between the VT1 base and the case, the diagram shows a capacitor in dotted lines (there is a place for it on the board). If the generator does not self-excite (due to low quartz activity), you need to solder a capacitor in this place, selecting it in the range of 120-180 pF for the maximum output oscillations. In the absence of the specified quartz, you can try to install the resonators at a frequency three times lower than the required one (9.04-9.046). The transmitter operates reliably when the supply voltage is reduced to 5 V.

Dnishchenko V. A.

500 schemes for radio amateurs. Remote control models.

St. Petersburg: Science and Technology, 2007. - 464 e.: ill.

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Stereo FM transmitter with frequency stabilization on quartz!
AHTUNG! Wrong translation from Chinese!

Producing stable firing frequencies slightly from the FM stereo radio transmitter has always been the desire of many, here is the scientific and technological development in Fujian crystal production center of frequency stabilization use in the stereo FM transmitter, it operates very stable, sound quality, well suited for home wireless use audio.

The photo shows the operation of the aircraft in accordance with the principle of the circuit; the circuit mainly consists of four parts: power supply circuits, stereo encoder circuits, crystal oscillator and RF amplifier circuit; U2 and LED light-emitting diodes and related components are the RC circuit power supply, U2 One 9V stable output voltage to use BA1404 and Q1Q2, light-emitting diodes as a power source in addition to the instructions, but also for BA1404 to ensure a stable operating voltage of about 2V. R5 is an LED current limiting resistor. C25, C26, C32, C33, C34 to power supply filter capacitor, R5, R13, R17 to power supply decoupling resistors, can be reduced at all levels, resulting in the use of the same power interference. And the surrounding components make up BA1404 FM stereo circuit coding, in which refusal to use their internal high frequency oscillator circuit, similar to using a stereo encoder. R1, R2, R3, R4 and C1-C10 are FM all the way and input matching networks, as well as a receiver to increase the network to be effective in improving frequency response results. L, R-two channels of audio signal to the stop of the network and the input matching the BA1404 input network, respectively 1 and 18 feet, encoded audio signal from 14 feet, 13 feet at the same time experimental 19KHZ output signal for synchronous demodulation by the LR signal receiver. Q2 and its surrounding components is a crystal oscillator circuit, then the oscillation frequency in the JZ2 crystal is decided to be in this figure at 13.09MHZ, IC1 output signal and audio encoding experimental signal amplifier circuit, consisting of Q1 is amplified into a crystal oscillator circuit, Q1 modulation level to be effective in increasing the frequency compensated. By choosing a varactor diode and crystal can effectively increase the compensated modulation frequency. Q3, Q4 is the RF amplifier power circuit, Q2Q3 is an octave, and also played the role of a power amplifier. By changing CV1CV2, you can multiply the frequency for RF 91.63MHZ (here over seven octaves), just landed in the FM radio range. Q4 in group C, and released more effective. L8, C40, and CV3, C41 form an RF filter and antenna coupling circuit, by adjusting the high frequency waveform of CV3 can be effectively transmitted to the antenna to reduce harmonic components. The machine has a power of about 1W, an external GP antenna used for launching in an open area measured approximately one kilometer near the launch.


The picture shows that according to the circuit board assemblies. L1, L2, L6, using color code inductance, L6 power should be selected no less than color coding inductance 1/8W, other inductors using a wire with a diameter of 0.51mm by a 3.3mm bit in the system around, circle on the map in the interlinear. C2053 can also choose Q4 radio output power more. The entire board is about 200 milliamperes of current. DC power supply output current must be selected at least 500 mA Input voltage to 12V DC adapter. If the power supply's output is not sufficient to produce hum, it is easy to affect the transmitter's performance.


Check all components are completed correctly after welding the rod is connected to the antenna or the GP antenna will be in the tuner area 91.63MHZ, power test machine to regulate CV1, LC resonant circuit in the frequency generator at N (where N = 7, that is, 13.090MHZ x 7 = 91.63 MHZ, FM88-108MHZ item), the largest output at the moment场强仪instructions, and then adjust the output of CV2 and CV3 to the largest fields. IN general scheme RF modulation offset relative to the frequency modulation compensated will be some slightly less, the performance output at the receiver will apparently be relatively small, it should meet the needs of normal reception. W1 can be adjusted to improve frequency modulation and compensate for stereo separation and sound quality.