Filling of wireless microphones FM range. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Filling of wireless microphones FM range. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Audio equipment

Comments on the article

It is the 15st century outside, and a wireless microphone with a modulated signal transmitted over a radio channel is used not only at concert venues, but also in everyday life (for example, for karaoke). The range - up to XNUMX m within the apartment - as a rule, is quite suitable for all households, and the ability to receive a signal from a microphone to a regular FM receiver allows the device to be used universally (for example, as a mini radio station for communication between rooms or a room and a loggia).

The power of the radio microphone is so low that it does not pose a danger of causing interference to registered radio stations, therefore such a device does not require registration with the State Communications Authority. You can buy a radio microphone at any radio store for almost a symbolic price (no more than 500 rubles). The author did just that in order to upgrade the radio microphone, and then share practical experience with readers.

The appearance of the MIC-140 radio microphone is shown in Fig.1.

Filling of wireless FM microphones

The radio microphone transmitter is a simple electronic device that can be assembled even on discrete elements (that is, on your own, devoting one or two free evenings to this lesson), and the receiver can be anything that allows you to receive frequency-modulated signals at frequencies of 88-98 MHz. As a rule, any modern FM receiver has an automatic frequency control (AFC), so there are no problems with the "leaving" of the tuning frequency.

The 98 MHz radio receiver included with the MIC-140 radio microphone is shown in Figures 2 and 3.

Filling of wireless FM microphones

The receiver is equipped with a telescopic antenna with a maximum length of 45 cm, however, as experiments with a radio microphone have shown, the receiver normally "picks up a signal" from a microphone within a 3-room apartment, even if the antenna is extended only 8 - 10 cm. and masking of the structure, it is advisable to replace it with a piece of flexible wire in insulation (for example, MGTF-0.8). This option is also verified by the author. The output of the radio receiver, if necessary, is connected through a special connector on its body to headphones (microtelephone headset) or (through another connector on its body) to a power amplifier working on dynamic heads.

Figure 4 shows the appearance of the radio microphone with the top cover removed.

Filling of wireless FM microphones

The dynamic microphone with a coil resistance of 200 ohms is clearly visible, the edge of the printed circuit board, rigidly fixed with glue inside the cylindrical body of the device, the battery compartment, the mode switch (radio microphone, wired microphone and off) and other parts of the case.

The type of dynamic microphone is unknown, but if you connect a domestic dynamic microphone MD-201 instead, the device works just as well.

Figure 5 shows the electrical circuit of the device.

Filling of wireless FM microphones

When the power is turned on with a switch on the microphone body, the power supply from the dry cell is supplied to the generator unit. The master oscillator is made on the transistor VT3. The operating point of this transistor is set using the divider R10-R11. Capacitors C7 and C8 - blocking. The load of the transistor VT3 is the circuit of the coil L1. Capacitors C4 and C5 form a capacitive divider. The amplitude and shape of the generator signals depend on the ratio of the capacitances of these capacitors. Frequency modulation is carried out using the BB105V varicap. The voltage on the varicap is supplied from a divider across resistors R7 and R8. with which the initial offset is set at the factory.

The modulating audio frequency voltage is supplied to the varicap from the collector of the transistor VT2. The frequency deviation can be changed by selecting the resistance of the resistor R9. The low frequency amplifier is made on transistors VT1 and VT2. The required gain for the transistor stage is set using resistors R1 and R2. The amplification of this stage on two transistors is sufficient for normal operation over the entire dynamic range of the microphone.

The WA1 antenna is a silver-plated wire twisted into a spiral with a diameter of 0,6 mm (the diameter of the spiral is 7 mm, the number of turns of the spiral is 38). "hidden" in a rubber pin. This pin, in turn, is put on the microphone using a 3-pin connector at the end of the microphone housing (Fig. 1). A longer antenna is not needed, as it would disrupt the generation of the master oscillator on the transistor VT1.

Manufacturers have made the MIC-140 wireless microphone universal; it can work both as an FM transmitter and as a regular microphone. In the latter case, two of the three pins of the connector are needed to connect the output signal of the microphone amplifier to the input of the power amplifier (by wire).

The power source for the wireless microphone is one AA battery with a voltage of 1.5 V. The current consumption is only 7 mA, which is enough for 3 hours of continuous operation of the transmitter. The continuous mode of the transmitter (radio microphone) is mentioned here for general information about the duration of the device from one battery. In reality, using a microphone in continuous transmission mode is rarely a stop-and-go. But even in this case, the device works reliably and is ready for overloads, because. the transmitter power is low, and the power supply voltage is only 1,5 V. which guarantees the operation of the VT3 transistor in the transmission mode without overloads.

Most of the elements are installed vertically on the printed circuit board (to save space in the microphone body). Coil L1 - frameless, contains 5 turns of silver-plated copper wire 00,8 mm. inner diameter - 7 mm, winding - with a step of 1,25 mm, taps - from the 1st and 2nd (from the beginning of the winding) turns.

The practical application of the radio microphone is truly diverse. Any portable transceiver or all-band receiver, for example, Kenwood TH-F7, tuned to the radio microphone frequency (in the case of the MIC-140, to 98 MHz) can receive a radio signal from this microphone.

Given the low cost of the radio microphone, in some cases it will not even be necessary to assemble its circuit on your own. It is enough to disassemble the microphone and carefully move its "stuffing" into another, more compact, case the size of, for example, a matchbox. The electrical circuit of the device and the principle of operation of the MIC-140 radio microphone are offered to readers to understand the principle of its operation and. will undoubtedly come in handy in case of modernization of this device or its repair.

Author: A.Kashkarov, St. Petersburg

See other articles Section Audio equipment.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

The threat of space debris to the Earth's magnetic field 01.05.2024

More and more often we hear about an increase in the amount of space debris surrounding our planet. However, it is not only active satellites and spacecraft that contribute to this problem, but also debris from old missions. The growing number of satellites launched by companies like SpaceX creates not only opportunities for the development of the Internet, but also serious threats to space security. Experts are now turning their attention to the potential implications for the Earth's magnetic field. Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics emphasizes that companies are rapidly deploying satellite constellations, and the number of satellites could grow to 100 in the next decade. The rapid development of these cosmic armadas of satellites can lead to contamination of the Earth's plasma environment with dangerous debris and a threat to the stability of the magnetosphere. Metal debris from used rockets can disrupt the ionosphere and magnetosphere. Both of these systems play a key role in protecting the atmosphere and maintaining ... >>

Solidification of bulk substances 30.04.2024

There are quite a few mysteries in the world of science, and one of them is the strange behavior of bulk materials. They may behave like a solid but suddenly turn into a flowing liquid. This phenomenon has attracted the attention of many researchers, and we may finally be getting closer to solving this mystery. Imagine sand in an hourglass. It usually flows freely, but in some cases its particles begin to get stuck, turning from a liquid to a solid. This transition has important implications for many areas, from drug production to construction. Researchers from the USA have attempted to describe this phenomenon and come closer to understanding it. In the study, the scientists conducted simulations in the laboratory using data from bags of polystyrene beads. They found that the vibrations within these sets had specific frequencies, meaning that only certain types of vibrations could travel through the material. Received ... >>

Random news from the Archive

Teenagers don't listen to their parents 23.05.2022

Many, many parents are faced with the fact that their child, only yesterday still obedient, suddenly turns into a difficult teenager who is clearly not interested in what dad and mom say, who does everything differently than he is told, who behaves as as if he does not hear the elders at all.

Employees of Stanford University found out that everything is true: teenagers do not hear their elders in the truest sense of the word. True, it’s not that they don’t hear - it’s just that the parental voice ceases to be the main one among the voices of other people.

What does cease to be the main mean? In past work, scientists have explored how the child's brain perceives the mother's voice. It turned out that the voice of the mother includes a number of zones in the child's brain, ranging from purely auditory to those responsible for self-awareness and facial analysis. Moreover, the mother's voice activates all these zones more strongly than the voice of an unfamiliar woman.

These experiments were done with children from 7 to 12 years old; for new experiments, children from 7 to 16 years old were already invited - and it turned out that the sixteen-year-old brain reacts to the mother's voice differently than the seven-year-old brain. The areas responsible for attention and anticipation of rewards, as they grow older, begin to respond more strongly to unfamiliar voices; the corresponding changes begin somewhere between thirteen and fourteen years of age. That is, it cannot be said that a teenager stops hearing his mother at all, just that if there is an alternative, he will listen with great attention to another voice, not necessarily a comrade of the same age, but simply an outside adult.

It may be difficult for some to come to terms with this, but not a single parent in the world will be able to install in a child the entire amount of knowledge that will be needed in life - and the ability to live in society also belongs to such knowledge. A person will encounter many other people with whom one needs to somehow negotiate, whose words need to be analyzed, whose emotions and thoughts need to be somehow understood, and the sooner the brain learns these procedures, the better. To learn, you need educational material, which is why the family world opens up into the external environment, and the ear begins to catch what others say first of all, instead of the long-familiar intra-family conversations.

However, such a switch to the outside world must depend on many different factors, and one of the main factors here, of course, is the relationship between the child and the mother. And these relationships are obviously influenced by other relatives, and here it would be interesting to know if the perception of the father's voice or the voice of brothers, sisters, etc. is somehow changing.

Other interesting news:

▪ Nanotube heatsinks

▪ Intel Core M processors for hybrid mobile computers

▪ The secret to strong beaver teeth

▪ Charger for any portable devices

▪ The laser controls the aircraft

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Preamplifiers. Article selection

▪ article Peace to huts, war to palaces. Popular expression

▪ article Why do sharks have a hard time sleeping? Detailed answer

▪ article Vietnamese zucchini. Legends, cultivation, methods of application