Encyclopedia of radio electronics and electrical engineering / Civil radio communications

 Comments on the article

S-METER FOR "LIGHTHOUSE"

This S-meter was developed for the Mayak radio station, which, in a converted form, is used by many radio amateurs to conduct communications on the 2-meter band. High sensitivity and good frequency properties allow it to be used in any VHF FM radio station.

S-meter for CB radio stations, which was described in the article by Yu. Vinogradov "Switch S-meter for CB radio stations" ("Radio", 1999, No. 6, p. 65). provides a relatively small range of indicated voltage and has a low sensitivity (10 mV at a frequency of 465 kHz). For this reason, it has to be turned on closer to the final stages of the IF path, which narrows the range of measured values ​​of the IF signal. In addition, sensitivity decreases with increasing IF, and this practically excludes the use of an S-meter in VHF FM radio stations with an IF from 10,7 to 24 MHz.

The scheme of the S-meter is shown in fig. 1. The basis of the device is the DA1 chip (K174UR5). It is used in the submodule of the radio channel of third-generation TVs and is inexpensive. As you know, this microcircuit contains amplifying stages of the IF (38 MHz), nodes of the AGC system, as well as a demodulator and nodes of the AFC system. Its advantages include a high gain and a wide range of operating frequencies (up to 40 MHz).

To eliminate the possible influence of the S-meter on the cascades of the radio station, a source follower on a field-effect transistor VT1 is installed at its input. On the field-effect transistor VT2, a DC voltmeter with a PA1 measuring head is assembled. With an increase in the input signal level of the IF, the constant voltage at pin 14 of the microcircuit will decrease and the arrow of the device will deviate. Diode VD1 and resistor R11 are used to expand the range of indicated voltage.

In the device, two copies of the microcircuit were alternately tested. In this case, the lower limit of the indicated voltage was in the range of 30...70 μV. and the upper one - 50 ... 150mV (measurement range - 60 ... 65 dB). The indicated levels correspond to the range of the input voltage of the K174URZ microcircuit. on which the FM detector of the Mayak radio station was built. Therefore, it is more convenient to turn on such an S-meter in this case in parallel with the input of this microcircuit. On the diagram of the radio station, this point is designated "KTZ".

LED HL1 provides an indication of the maximum level of the received signal. It starts to glow when the input signal level is 250...400 mV. i.e. 10 ... 15 dB above the limit value indicated by the pointer device.

It is necessary to power the device from a stabilized power source, since the stability of the calibration depends on this. Current consumption - about 45 mA.

The device can use transistors KP303A, KP303B. LED HL1 - any small-sized with a working current of 5 ... 10 mA. Diode VD1 - KD419B or another detector, or rectifier with a Schottky barrier. Capacitor C7 - K50. K52, K53, the rest are non-polar - KM, K 10-17 KD. Trimmer resistors - SPZ-19, constants - MLT, S2-33. Measuring head RA1 - with a total deflection current of 100 ... 200 μA and a loop resistance of 2 ... 3 kOhm. for example, M4247.

Most parts of the device are placed on a printed circuit board made of double-sided foil fiberglass, a sketch of which is shown in Fig. 2. The second side of the board is left metallized. Holes in the board, into which the leads of parts that are not connected to a common wire are inserted, are countersunk. The common wire foil is connected in several places to the common wire on the other side of the board.

Connect the S-meter to the radio station after the main selection filter or to the cascades after it. Resistor R1 is placed on the radio board and connected to the S-meter board (capacitor C1) with a shielded wire of minimum length.

The adjustment of the device begins with the setting of "zero" by the resistor R12 in the absence of an input signal. Resistor R10 sets the slope of the S-meter characteristic in the left half of the instrument scale, and R11 - in the right. By selecting the resistor R1, the minimum limit of the indicated voltage range is set. If, with an increase in the input signal from the minimum, a small current jump is observed through the RA 1 microammeter (10 ... 15 μA), then resistor R7 must be selected. After that, the setting should be repeated.

The table shows the input signal levels and the corresponding values ​​of the S scale (for VHF bands and the input impedance of the receiver is 50 Ohm).

If the sensitivity of the radio station is 0,15 μV (4 points), then this level should be assigned to the 5 μA division of the PA1 measuring head. In this case, the S-meter will indicate levels from four points to S9 + 45 dB. and the level of nine points will correspond to approximately 50 ... 60 μA, i.e. the scale is quite convenient.

LOW-NOISE 430 MHz ANTENNA AMPLIFIER

The amplifier circuit is shown in fig. 1. It is assembled on a low-noise gallium arsenide field-effect transistor VT1. The resonant circuits L1C1 and L3C5 at the input and output of the amplifier provide FET matching and frequency selection. The bandwidth of the amplifier is about 10 MHz, and the gain is 10 ... 14 dB. Both parameters depend on the connection points of the input and output cables. Diodes VD1 ... VD4 protect the transistor from breakdown by a powerful transmitter signal or discharges of static electricity.

The supply voltage of the field-effect transistor (+5 V) is stabilized by an integrated voltage regulator on the DA1 chip

The amplifier is assembled on a printed circuit board made of double-sided foil fiberglass 1,5 mm thick, a sketch of which is shown in fig. 2. The second side is left metallized and connected along the contour with a foil to the common wire of the first side. The inductors are made in the form of printed conductors.

It is desirable to use unpackaged permanent capacitors in the device - K10-17B, KM-ZV, KM-4V, KM-5V, in extreme cases, you can use ordinary small-sized ceramic ones, shortening their leads to a minimum length. Trimmer capacitors - KT4-25; resistors - MLT, R1-4, R1-12. Choke L2 contains 10 turns and is wound with wire PEV-2 0,2 on a mandrel with a diameter of 3 mm. After mounting, the drain terminal of the transistor should be filled with a small amount of epoxy resin filled with carbonyl iron powder. This will greatly increase the stability of the amplifier.

Establishment begins with setting the drain current of the field-effect transistor, corresponding to the minimum noise figure for this type of transistor (5 mA). The point of connection of the input cable is selected according to the maximum sensitivity, and the output cable - according to the maximum transmission coefficient. The input circuit is tuned to the middle frequency of the range by capacitor C1, and the output circuit by capacitor C5.

If the amplifier is planned to be placed near the antenna, then it should include two relays, necessarily coaxial high-frequency ones. If the amplifier is installed in the receiving part of the radio station after the receive / transmit switch, then the diodes VD3, VD4 can be excluded.

Author: I.Nechaev (UA3WIA)

See other articles Section Civil radio communications.

Read and write useful comments on this article.

<< Back

<< Back

Latest news of science and technology, new electronics:

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Controlling objects using air currents 04.05.2024

The development of robotics continues to open up new prospects for us in the field of automation and control of various objects. Recently, Finnish scientists presented an innovative approach to controlling humanoid robots using air currents. This method promises to revolutionize the way objects are manipulated and open new horizons in the field of robotics. The idea of ​​controlling objects using air currents is not new, but until recently, implementing such concepts remained a challenge. Finnish researchers have developed an innovative method that allows robots to manipulate objects using special air jets as "air fingers". The air flow control algorithm, developed by a team of specialists, is based on a thorough study of the movement of objects in the air flow. The air jet control system, carried out using special motors, allows you to direct objects without resorting to physical ... >>

Purebred dogs get sick no more often than purebred dogs 03.05.2024

Caring for the health of our pets is an important aspect of the life of every dog ​​owner. However, there is a common assumption that purebred dogs are more susceptible to diseases compared to mixed dogs. New research led by researchers at the Texas School of Veterinary Medicine and Biomedical Sciences brings new perspective to this question. A study conducted by the Dog Aging Project (DAP) of more than 27 companion dogs found that purebred and mixed dogs were generally equally likely to experience various diseases. Although some breeds may be more susceptible to certain diseases, the overall diagnosis rate is virtually the same between both groups. The Dog Aging Project's chief veterinarian, Dr. Keith Creevy, notes that there are several well-known diseases that are more common in certain breeds of dogs, which supports the notion that purebred dogs are more susceptible to disease. ... >>

Random news from the Archive Battery origami 26.06.2015 Scientists from Arizona State University (USA) have developed lithium-ion batteries that can change their shape, increasing by more than one and a half times. The battery itself (more precisely, its individual elements) is covered with paper with a thin layer of polymer insulator, which takes all the loads on the battery. To provide flexibility in design, the paper plates are cut in a manner similar to kirigami, a variation of the Japanese art of origami paper folding. The plates are interconnected by narrow strips, which makes it possible for them to change their relative position in space without any gaps. This allows the battery to fold, reshape, or stretch without harming the individual battery cells. In the future, such batteries can be used in any flexible electronic structures and even clothing items.

Other interesting news:

▪ Flash card 64 Mbit DataFlash from ATMEL

▪ Rheumatics and athletes - in the cold

▪ Egg white from microbes

▪ MIPI CSI-2 v2.0 specification introduced

▪ MSP-EXP432P401R IoT Development Board

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Palindromes. Article selection

▪ article To whom is a donut, and to whom is a hole from a donut. Popular expression

▪ article How is butter made? Detailed answer

▪ article Work on a lid-making machine such as VD-14, etc.. Typical instructions for labor protection

▪ article Acoustic light switch. Encyclopedia of radio electronics and electrical engineering

▪ article Pulsating faces. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

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

www.diagram.com.ua
2000-2024