Encyclopedia of radio electronics and electrical engineering / Civil radio communications

 Comments on the article

A high-frequency signal generator is necessary for the repair and tuning of radio receivers and therefore is quite in demand. The Soviet-made laboratory generators available on the market have good characteristics, as a rule, they are redundant for amateur purposes, but they are quite expensive and often require repair before use. Simple generators of foreign manufacturers are even more expensive and at the same time do not differ in high parameters. This forces radio amateurs to manufacture such devices on their own.

The generator is designed as an alternative to simple industrial devices similar to GRG-450B [1]. It works in all broadcasting ranges, its manufacture does not require winding of inductors and laborious adjustment. The device has extended HF bands, which made it possible to abandon a complex mechanical vernier, a built-in millivoltmeter of the output signal, and frequency modulation. The device is made from cheap common parts that any radio amateur who repairs radios can find.

An analysis of many amateur designs of such generators revealed a number of common disadvantages characteristic of them: a limited frequency range (most cover only the DV, MW and HF ranges); significant frequency overlap in the high-frequency ranges makes it difficult to accurately set and leads to the need to manufacture a vernier. Often winding of inductors with taps is required. In addition, descriptions of these structures are too brief, and often absent altogether.

It was decided to independently design a high-frequency signal generator that meets the following requirements: an extremely simple circuit and design, inductors without taps, the absence of self-made mechanical components, operation in all broadcast bands, including VHF, extended bands and electric vernier. A 50 ohm coaxial output is desirable.

Table

¹⁾ At the coaxial output with a load resistance of 50 ohms, effective value.
²⁾ With the variable capacitor disconnected and the voltage across the varicap 0...5 V.

As a result of checking many technical solutions and repeated improvements, the device described below appeared. The frequency ranges generated by it are indicated in the table. The generator frequency setting accuracy is no worse than ±2 kHz at a frequency of 10 MHz and ±10 kHz at a frequency of 100 MHz. Her departure per hour of operation (after an hour of warm-up) does not exceed 0,2 kHz at a frequency of 10 MHz and 10 kHz at a frequency of 100 MHz. The same table shows the maximum effective values ​​of the output voltage in each range. The non-linearity of the millivoltmeter scale is no more than 20%. The supply voltage is 7,5 ... 15 V. The signal generator circuit is shown in fig. 1.

Rice. 1. Signal generator circuit (click to enlarge)

As a rule, oscillators with a point-to-point connection of an oscillating circuit, capable of operating at a frequency of more than 100 MHz, generate a distorted square wave rather than a sinusoid in the medium wave range. To reduce distortion, a significant change in the operating modes of the active elements of the generator is required depending on the frequency. The signal of the master oscillator used in the described device with field-effect and bipolar transistors connected in series in direct current [2] has much less distortion. They can be reduced by adjusting the operating mode of the bipolar transistor only.

At low-frequency ranges, the operation mode of the transistor VT2 is set by resistors R1 and R9 connected in series. With the transition to high-frequency ranges, switch SA1.2 closes resistor R1. To increase the steepness of the characteristics of the field-effect transistor VT1, a constant bias equal to half the supply voltage is applied to its gate. The supply voltage of the master oscillator is stabilized by the integral stabilizer DA1. Resistor R10 serves as the minimum load of the regulator, without which its output voltage is clogged with noise.

Industrial-made chokes are used as inductors L1-L10 of the master oscillator. They are switched by switch SA1.1. In the VHF2 range, the inductance L11 is a piece of wire about 75 mm long, connecting the switch to the printed circuit board.

The deviation of the actual inductance of the inductor from the nominal one can be quite significant, so the range boundaries are chosen with some overlap in order to exclude their laborious installation. The limits of the ranges indicated in the table were obtained without any selection of chokes. It is preferable to use large chokes, the stability of the inductance of which (and therefore the generated frequency) is higher than that of small ones.

For frequency tuning, the device uses a three-section variable capacitor with a gearbox, which was used in the Okean radio receivers, the Melodiya radiograms and many others. So that its body does not have electrical contact with the body of the device, it is fixed inside it through an insulating gasket. This made it possible to include one section of the capacitor in series with two others connected in parallel. This is how extended HF bands are implemented. In the DV, SV1 and SV2 ranges, where a large frequency overlap is required, the SA1.2 switch connects the variable capacitor case to a common wire. In the ranges of KV6, UKV1 and UKV2, the variable capacitor is switched off by the SA2 switch. When the switch is closed, the stable generation frequency does not exceed 37 MHz.

In parallel with the variable capacitor, a circuit of the varicap matrix VD1, capacitors C6, C9 and resistor R6 is connected, which serves as a frequency modulator, an electric vernier, and when the variable capacitor is turned off, it is the main tuning element. Since the amplitude of the high-frequency voltage on the oscillatory circuit reaches several volts, the matrix varicaps connected in anti-series introduce much less distortion than a single varicap would introduce. The tuning voltage for the varicaps of the VD1 matrix comes from the variable resistor R5. Resistor R2 somewhat linearizes the tuning scale.

The generator's frequency modulation signal is fed to the XS1 connector from any external source. When setting up and testing an AM radio receiver, the conversion of frequency modulation into amplitude modulation occurs in it itself due to the uneven frequency response of the pre-detector part of the receiving path. You can observe the AM signal on the last IF circuit of the receiver using an oscilloscope. Such a solution is not always acceptable, but simple amplitude modulators used in amateur designs of measuring generators create strong spurious frequency modulation even in low-frequency HF bands, which makes it almost impossible to use them for their intended purpose. A sawtooth voltage is applied to the XS2 connector when using the device as a sweep frequency generator.

The master oscillator is connected to the output follower on the transistor VT4 through the capacitor C12, the extremely small capacitance of which reduces the effect of the load on the generated frequency and the decrease in the amplitude of the output voltage at a frequency above 30 MHz. To partially eliminate the decrease in amplitude at a low frequency, the capacitor C12 is shunted by the R11C14 circuit. A simple emitter follower with a high output impedance on a bipolar transistor turned out to be the most suitable solution for such a wideband device. The effect of load on frequency is comparable to that of a FET source follower, and the amplitude versus frequency dependence is much smaller. The use of additional buffer stages only worsened the decoupling. To ensure good decoupling in the DV-KV ranges, the VT4 transistor must have a high current transfer coefficient, and in the VHF ranges, extremely small interelectrode capacitances.

The repeater output is connected to the XT1.4 terminal, which is mainly intended for connecting a frequency meter, which leads to a slight decrease in the output voltage. The internal resistance of this output on the HF bands is about 120 ohms, the output voltage is more than 1 V. The diodes VD2, VD3, the transistor VT3 and the LED HL1 have an indicator of the presence of RF voltage at the output of the repeater.

From the engine of the variable resistor R18, which serves as an output voltage regulator, the signal goes to the R19R20 divider, which, in addition to additional decoupling of the generator and the load, provides the output impedance of the coaxial output (XW1 connector) on the HF bands close to 50 ohms. On VHF, it drops to 20 ohms.

The frequency deviation when the position of the R18 slider changes from the upper position to the lower one according to the scheme reaches 70 ... 100 kHz at a frequency of 100 MHz without load, and with a 50 Ohm load connected - no more than 2 kHz (at the same frequency).

To measure the output voltage at connector XW1, a detector is provided, made on resistors R15, R17, diode VD4 and capacitor C17. Together with an external digital voltmeter or multimeter in voltmeter mode, connected to contacts XT 1.3 (plus) and XT1.1 (minus), it forms a millivoltmeter of the effective value of the generator output voltage. To obtain a more linear scale, a constant bias voltage of 4 V is applied to the diode VD1, which is set by a multi-turn trimmer resistor R17.

The external voltmeter must have a measurement limit of 2 V. In this case, a unit will be constantly displayed in the highest digit of its indicator, and the measured output voltage in millivolts in the lower digits. The minimum measured voltage is about 20 mV. Above 100 mV readings will be slightly higher. At a voltage of 200 mV, the error reaches 20%.

The generator is fed from a stabilized DC voltage source of 7 ... 15 V or from a battery. With an unstabilized power supply, the generated high-frequency signal will inevitably be modulated at a frequency of 100 Hz.

The installation of the generator should be approached very carefully, the stability of its parameters depends on this. Most of the parts are mounted on a printed circuit board made of insulating material foiled on both sides, shown in fig. 2.

Rice. 2. Printed circuit board made of insulating material foiled on both sides

Rice. 3. Location of parts on the board

The location of the parts on the board is shown in fig. 3. The common wire foil pads on both sides of the board are interconnected by wire jumpers soldered into the holes, which are shown filled. After mounting, the elements of the output repeater are closed on both sides of the board with metal screens, the contours of which are shown by dashed lines. These screens must be securely, soldered around the perimeter, connected to the common wire foil. In the screen, located on the side of the printed conductors, above the contact pad to which the emitter of the VT4 transistor is connected, a hole is made through which a copper pin soldered to this pad passes. Later, the central core of the coaxial cable is soldered to it, going to the variable resistor R18 and the capacitor C18. The cable braid is connected to the repeater screen.

The generator mainly uses fixed resistors and capacitors for surface mounting of size 0805. Resistors R19 and R20 are MLT-0,125. Capacitor C3 - oxide with low ESR, C7 - oxide tantalum K53-19 or similar. Inductors L1-L10 - standard chokes, preferably domestic series DPM, DP2. Compared to imported ones, they have a much smaller inductance deviation from the nominal one and a higher quality factor.

In the absence of a choke of the required rating, the L10 coil can be made independently by winding eight turns of wire with a diameter of 0,08 mm onto an MLT-0,125 resistor with a resistance of at least 1 MΩ. As an inductance L11, a piece of a rigid central wire from a coaxial cable about 75 mm long is used.

Three-section variable capacitors with a gearbox are extremely common, but if one is not available, a two-section one can also be used. In this case, the capacitor housing is connected to the device housing, and each section is connected through a separate switch, and one of the sections is connected through a stretching capacitor. It is much more difficult to control a device with such a variable capacitor.

Switch SA1 - PM 11P2N, similar switches of the PG3 or P2G3 series are also applicable. Switch SA2 - MT1. The variable resistor R18 is SP3-9b, and it is not recommended to replace it with a variable resistor of another type. If the variable resistor indicated in the circuit was not found, then you can replace it with a lower value, but you need to increase the resistance of the resistor R16 so that the total resistance of the parallel-connected resistors R16 and R18 remains unchanged. Variable resistor R5 - any type, R17 - imported multi-turn trimmer 3296.

Diodes GD407A can be replaced with D311, D18, and diode 1 N4007 - with any rectifier. Instead of the varicap matrix KVS111A, it is allowed to use KVS111B, instead of 3AR4UC10 - any red LED.

The master oscillator is insensitive to the types of transistors used. The field effect transistor KP303I can be replaced by KP303G-KP303Zh, KP307A-KP307Zh, and with the correction of the printed circuit board - by BF410B-BF410D, KP305Zh. For transistors with an initial current of more than 7 mA, resistor R7 is not required. The bipolar transistor KT3126A can be replaced by any pnp microwave transistor with minimal interelectrode capacitances. As a replacement for the KT368AM transistor, SS9018I can be recommended.

Connector XW1 - type F. Any cable can be easily embedded into it, and if necessary, you can simply insert a wire. Clamping block XT1 - WP4-7 for connecting acoustic systems. Connectors XS1 and XS2 are standard 3,5 mm mono jacks.

The generator is assembled in a case from a computer power supply. Its installation is shown in the photograph of Fig. 4. Remove the fan grille, and cover the side of the case where it was located with a sheet steel plate with holes for connectors and controls. To fix the plate, use all the screw holes in the case.

Rice. 4. Mounting the generator

Mount the board on a brass stand 30 mm high, next to the SA1 switch, with printed conductors facing up. Tin the contact point of the rack with the case and place a contact tab under it, which is connected to the screen of the output repeater. If possible, avoid the formation of large closed circuits of the flow of high-frequency current through the common wire, leading to a decrease in the output voltage on the VHF bands.

Place the variable resistor R18 in an additional metal screen, clamping it under the resistor flange. Installation of resistors R19 and R20 - hinged. Connect their common point to connector XW1 with a coaxial cable. Install the detector elements of the millivoltmeter on a small circuit board, which you fix directly on the connector XW1.

Install the variable capacitor C4 in the housing through the insulating gaskets. It is advisable to make a dielectric extension of the capacitor axis, on which the tuning knob will be put on. But this is not necessary, it is permissible to put it on the axis of the capacitor itself. Connect the variable capacitor to the SA2 switch and to the board with a rigid central core from the coaxial cable. Capacitor C5 install and connect to the case next to the capacitor C4.

Before installing the switch SA1 into the device, mount inductors L1-L10 and resistor R1 on it. The axes of neighboring coils must be mutually perpendicular, otherwise their mutual influence cannot be avoided. This is especially true for the low frequency ranges. It is convenient to alternate coils with axial and radial leads. Connect the common wire to SA1.1 with a bundle of ten or more MGTF wires. With a separate wire, connect the resistor R1 and the movable contact of the SA1.2 biscuit to the common wire.

Using a syringe with a shortened needle, apply all the necessary inscriptions on the front panel with tinted zapon varnish. Mount the sawtooth voltage input connector XS2 on the rear panel to prevent accidental connection to it. Connect the power cord there as well. It is duplicated by contacts XT1.1 (minus) and XT1.2 (plus), from which you can power other measuring instruments or a custom device. Close all extra holes in the case with steel plates soldered to it.

Assembled according to the recommendations, the device should work immediately. You should measure the DC voltage at the emitter of the transistor VT4. With the upper (according to the scheme) position of the variable resistor R18 slider, it should not be less than 2 V, otherwise it is necessary to reduce the resistance of the resistor R13. Next, you need to check the operation of the generator on all ranges. On VHF, with a large input capacitance of the variable capacitor (if it is turned on), the oscillations are stalled, as can be seen from the decrease in the brightness of the HL1 LED.

If the variable resistor R5 is included, as shown in the diagram, then the tuning band on the VHF bands will not exceed 15 MHz, and it may be necessary to lay these bands within the broadcast limits. First of all, do it in the VHF1 range (65,9 ... 74 MHz) using the trimmer capacitor C9 with the SA2 switch open. Next, move the SA1 switch to the VHF2 position and, by changing the length of the piece of wire that serves as the inductance L11, achieve coverage of the broadcast range of 87,5 ... 108 MHz. If you need to greatly increase the frequency, a piece of wire can be replaced with a strip of copper foil or a flattened braid of a coaxial cable. The frequency tuning limits of the varicap can be significantly increased if the variable resistor R5 is supplied with voltage from the input, and not from the output of the integral stabilizer DA1. But this will lead to a noticeable deterioration in frequency stability.

Adjustment of the millivoltmeter detector consists in setting a voltage of 17 mV with a trimming resistor R1010 on a multimeter connected to the output of the detector at zero output voltage of the generator (the variable resistor R18 engine is in the lower position according to the diagram). Further, by increasing the output voltage range to 280 mV with a variable resistor (controlled by an oscilloscope), adjust R17 so that the multimeter shows 1100 mV. This corresponds to an effective value of the output voltage of 100 mV. It should be borne in mind that RF voltage less than 20 mV cannot be measured with this millivoltmeter (dead zone), and at a voltage of more than 100 mV, its readings will be very high.

It is recommended to turn on the generator one hour before the start of measurements. After it warms up, the long-term frequency stability will increase significantly.

The PCB file in Sprint Layout 6.0 format can be downloaded from ftp://ftp.radio.ru/pub/2016/01/gener.zip.

Literature

1. High-frequency signal generator GRG-450B. - URL: printsip.ru/cgi/download/instr/GW_instek/generatori_gw/grg-450b.pdf.
2. Shortwave GIR (Abroad). - Radio, 2006, No. 11, p. 72, 73.

Author: G. Bondarenko

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:

A New Way to Control and Manipulate Optical Signals 05.05.2024

The modern world of science and technology is developing rapidly, and every day new methods and technologies appear that open up new prospects for us in various fields. One such innovation is the development by German scientists of a new way to control optical signals, which could lead to significant progress in the field of photonics. Recent research has allowed German scientists to create a tunable waveplate inside a fused silica waveguide. This method, based on the use of a liquid crystal layer, allows one to effectively change the polarization of light passing through a waveguide. This technological breakthrough opens up new prospects for the development of compact and efficient photonic devices capable of processing large volumes of data. The electro-optical control of polarization provided by the new method could provide the basis for a new class of integrated photonic devices. This opens up great opportunities for ... >>

Primium Seneca keyboard 05.05.2024

Keyboards are an integral part of our daily computer work. However, one of the main problems that users face is noise, especially in the case of premium models. But with the new Seneca keyboard from Norbauer & Co, that may change. Seneca is not just a keyboard, it is the result of five years of development work to create the ideal device. Every aspect of this keyboard, from acoustic properties to mechanical characteristics, has been carefully considered and balanced. One of the key features of Seneca is its silent stabilizers, which solve the noise problem common to many keyboards. In addition, the keyboard supports various key widths, making it convenient for any user. Although Seneca is not yet available for purchase, it is scheduled for release in late summer. Norbauer & Co's Seneca represents new standards in keyboard design. Her ... >>

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. ... >>

Random news from the Archive Medicines for old age 16.03.2013 Renowned Harvard scientist David Sinclair has announced a breakthrough in the development of drugs that can block the aging process. According to the scientist, in 5 years there will be drugs that can extend life up to 150 years. Sinclair's article, published in Science, explains that interaction with a single amino acid in the SIRT1 enzyme is critical to the development of life-extending drugs. SIRT1 controls DNA repair, apoptosis (cell death), circadian rhythms, inflammatory pathways, insulin secretion, and mitochondrial biogenesis at the cellular level. SIRT1 is an enzyme in a class of molecules called sirtuins. Recent studies show that sirtuin activation reduces the rate of cell aging through interaction with other cellular "switches" such as FOXO3a and PGC-1a. Resveratrol, a polyphenol found in red wine and grapes, is a weak natural sirtuin activator and has been shown to prolong life in mice in some studies. However, data on sirtuin activators are conflicting, and direct activation of SIRT1 is considered incredibly difficult, since there has never been a drug in the history of pharmaceuticals that could harmlessly speed up the enzyme. However, the search for a cure for senile diseases led to the fact that in 117 experiments, scientists were able to confirm the ability of individual substances to activate SIRT1. Now Harvard scientists know exactly how to activate the enzyme and have a good understanding of the molecular mechanism of activation. Thus, the mechanism of allosteric activation (as in the case of resveratol) allows the development of drugs for the treatment of many diseases associated with aging. A "side effect" of this therapy will be life extension up to approximately 150 years. According to David Sinclair, the "longevity pill" will be on sale in the coming decades. At the same time, "drugs for old age" will be ready within 5 years, but it will take a long time to test them and confirm their effectiveness. "In fact, the new drugs will treat one disease, but unlike current drugs, prevent 20 other diseases," says Sinclair. "In essence, we will be able to slow down aging. Some of us could live up to 150 years."

Other interesting news:

▪ MAX22192 - 8-channel digital input driver with galvanic isolation

▪ What do poisonous mushrooms smell like?

▪ Artificial wood from the laboratory

▪ Samsung Gear VR Innovator Edition - virtual reality glasses for smartphones

▪ Hot Springs of Mars

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Parameters of radio components. Article selection

▪ article Barcode. History of invention and production

▪ Article What is the difference between registered and preferred shares? Detailed answer

▪ article Carbine brake. Tourist tips

▪ article Transistor transmitter for the 432 MHz band. Encyclopedia of radio electronics and electrical engineering

▪ article Low-voltage voltage stabilizers. Encyclopedia of radio electronics and electrical engineering

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