Radio microphone with loop antenna. Scheme, description

Free technical library

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

Radio microphone with loop antenna. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

Comments on the article

In low-power transmitters of radio microphones operating in the 65 ... 73 MHz bands, radio amateurs most often use an ordinary piece of wire as an antenna (see, for example, the article by I. Sevastyanov "Radio Microphone" in "Radio", 1992, No. 10, p. 44, 45). However, as practice has shown, when operating such devices in the VHF band, a slight change in the transmitter frequency is observed with a decrease or increase in the distance between the human body and a freely hanging wire-antenna. It would be recommended to use a whip antenna. But using a radio microphone with such an antenna is extremely inconvenient, since the length of the pin should be commensurate with a quarter of the wavelength and for the VHF band it should be about 110 cm.

I offer radio amateurs the antenna I tested in the form of a spiral of wire with a diameter of 1 mm (Fig. 1). The spiral can be of any shape, it is only important that the total length of the wire is 85 ... 100 cm. I used such an antenna in a radio microphone, the diagram of which is shown in fig. 2. The low-frequency signal of the BM1 microphone is amplified by an amplifier-modulator on transistors VT1, VT2 and fed to the master oscillator circuit on the transistor VT3, the frequency of the circuit is changed by the tuning capacitor C8. From the output of the master oscillator, the modulated signal is fed to the power amplifier on the VT4 transistor and then goes to the transmitter antenna WA1.

(click to enlarge)

I recommend to assemble the master oscillator on the same board with a power amplifier, and it is desirable to place the first one in a metal screen, while the second one is not necessary to be shielded. The circuit coil L1 should be rigidly fixed on the board, since its movement when shaking the radio microphone affects the frequency stability of the master oscillator.

When mounting the radio microphone, fixed resistors MLT-0,125 were used, a variable resistor R1 - SDR, capacitors - any small-sized ones. Coils L3, L4, L5, L8, L9 are frameless and wound with PEL 0,8 wire. Coil 13 contains 7, L4,18 - 4, L5,19 - 9 turns. The inner diameter of the coils is 10 mm. Coils L4 and L8 are wound turn to turn, the gap between the turns of coils L3, L5, L9 is about 1 mm. Inductors L1, L2, L6, L7 are wound turn to turn on matches and contain 45-55 turns of PEL 0,1 wire. The radio microphone uses an MEK-3 electret microphone from a domestic portable tape recorder. The colors of the wires suitable for it are indicated in the diagram.

To set up a radio microphone, you will need a simple avometer (for example, Ts-20) and a field indicator (Fig. 3). The pointer indicator is used from a portable tape recorder. The field indicator coil L1 contains 6 turns of PEL 0,8 wire with a tap from the middle, winding in 1 mm increments. A piece of insulated wire 10 ... 15 cm long was used as its antenna.

Radio microphone with loop antenna

First, the master oscillator is set up, and then, paired with it, according to the largest deviation of the field indicator arrow, is a power amplifier. The generator must be tuned to a section of the VHF band free from broadcasting stations. The range of the radio microphone is about 150 m. The radio microphone is powered by the Krona battery, one battery is enough for 30 hours of operation.

Author: V. Razmatov, Syrdarya, Uzbekistan; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

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 ... >>

Random news from the Archive

Chainsaw with microprocessor 01.02.2014

Husqvarna has developed smart chainsaw technology that adapts the tool to any working conditions.

The AutoTune system for automatic control and power management of the engine is distinguished by the special structure of the carburetor and the presence of a microprocessor in it, which is responsible for the operation of the main systems. Simply put, AutoTune registers and takes into account the operating conditions and mode of operation of the chainsaw: fuel quality, carburetor temperature, engine speed, air filter contamination, etc. The received information is processed by a microprocessor that regulates the carburetor fuel supply, ensures constant high engine performance and prevents overload . Such characteristics allow the efficient use of gasoline vehicles even in extreme weather conditions or with poor quality fuel, Husqvarna notes.

Activation of the system does not require special skills from the user. It occurs automatically when the saw is started. It takes 3 to 5 minutes of work under load to fully scan the source data and adjust the carburetor, after which the tool functions as efficiently as possible. In addition, AutoTune optimizes the performance of the engine during cold start, which prevents it from overloading and further breakdowns.

Another unique feature of AutoTune is the ability to connect to a PC using special software for diagnosing the condition of the saw. A similar operation can be carried out at an authorized Husqvarna dealer for an inspection or repair. The processor built into AutoTune records the history of all the main performance indicators: engine errors, the number of working hours, temperature conditions, etc. Displayed on the screen, this information allows you to accurately determine the causes of possible malfunctions or take preventive measures.

The software allows you to check the correct operation of the sensors themselves used by the system.

Other interesting news:

▪ superMHL/HDMI 2.0 port processor

▪ Magnetic sheet

▪ CD as a dosimeter

▪ Thought controls the genes

▪ External battery for Sanho HyperMac laptops

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Voltage stabilizers. Article selection

▪ article Filming a wedding. video art

▪ article How Libraries Originated? Detailed answer

▪ article Tansy red. Legends, cultivation, methods of application

▪ article Car amplifier 70 W. Encyclopedia of radio electronics and electrical engineering

▪ article Three-way surround sound speaker. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews