A simple RF generator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple RF generator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The proposed radio frequency (RF) signal generator can be used to tune amateur radio antennas. It will also be useful in setting up receiving and transmitting equipment.

Radio amateurs for "silent" tuning of communication antennas (without turning on the transmitter) are developing various RF generators that are used to power bridge and panoramic devices. As a rule, such generators are assembled according to classical schemes and are based on the use of resonant circuits. Frequency tuning in them is carried out either by a variable capacitor, or by changing the capacitance of the varicap.

These generators are laborious to manufacture, as they contain inductors. But most importantly, when tuning over the range, the output signal level changes, which leads to the need to adjust the level before each measurement.

Control voltage, V	Frequency, MHz
2,62	20
2,8	25
2,98	30
3,12	35
3,29	40
3,46	45
3,66	50

These circumstances prompted the search for non-standard methods for generating radio frequency (RF) sinusoidal oscillations using digital microcircuits of wide application. The K531GG1 chip turned out to be the most suitable, which is capable of generating sinusoidal oscillations in the frequency band of 15 ... 60 MHz at a constant output signal level.

The radio frequency generator (Fig. 1) is designed to power bridge and panoramic SWR meters, frequency response meters. Its tuning range is 20 ... 50 MHz, the power at a load of 50 ohms is at least 200 mW.

Simple RF Generator

The basis of the device is a master oscillator (MG) on a DD1 chip. Broadband amplifiers are made on transistors VT1 and VT2. The frequency of the ZG depends on the voltage taken from the potentiometer R2 slider. Depending on the capacitance of the capacitor C2 and the resistance of the resistor R3, two generation modes are possible: broadband in the range of 20 ... ), in this case, the resistor R50 should have a resistance of 3 kOhm. To obtain a different tuning range, it is necessary to include an additional resistor between the top output R470 according to the circuit and the cathode VD5.

The dependence of the frequency on the control voltage at pin 2 of the DD1 chip is shown in the table. This dependence is almost linear and has a tuning slope of 20,8 MHz/V. Therefore, the frequency can be set using an external digital millivoltmeter connected to the XS1 connector.

The signal from the output of the DD1 chip is fed to the base of the transistor VT1. The load of this stage is the resistor R5 and the corrective inductance L1. Trimmer resistor R6 can adjust the output level.

A feature of the amplifying stage on the transistor VT2 is the stabilization of the base current (resistors R7, R8, diodes VD2 - VD4). This circuit design reduces the influence of the load on the output signal level and eliminates the overload of the cascade when the load is disconnected.

The generator can be powered either from a 12...15 V source (car on-board network or transceiver power supply) via XS3 connector, or from a 9 V battery compartment of a portable radio station (XS2 connector). This can be useful when working in the field, such as near an antenna on the roof of a building. Consumed current - no more than 150 mA.

Variable resistor R2 - SPO-1 group A with a vernier device, trimmer resistor R6 - SDR-386. the rest - MLT-0,125. Trimmer capacitor C1 - PDA (KT4-23), the rest - KM. Coil L1 is frameless, wound with PEV 0.31 wire on a mandrel with a diameter of 4.5 mm and contains 10 turns. L2 - unified choke DM-1 with an inductance of 10 μH. High-frequency connector XW1 - SR-50-73PV. XS1-XS3 - any low-frequency. SA1 - small-sized toggle switch with two positions.

The generator is mounted on a printed circuit board made of one-sided foil fiberglass, a sketch of which is shown in fig. 2.

Simple RF Generator

The board is placed in a metal screen. The device can be made in the form of an independent design or be part of another device with which it is supposed to work together.

The assembled generator starts working immediately. Establishment comes down to setting the required frequency range using a tuning capacitor C1 and selecting a resistor R3. Then it is necessary to remove the dependence of the generated frequency on the control voltage. This will require a digital frequency counter and a multimeter.

The device can perform the function of a sweeper when a sawtooth voltage is applied to the XS1 connector. It is also easy to carry out frequency modulation if you apply an audio frequency signal to XS1, and amplitude modulation (for this you need to apply a 3H signal to point "A").

In the author's version, the generator is tuned to a range of 25 ... 30 MHz and is placed in the same housing with a bridge SWR meter.

Author: B.Tatarko, Tver

See other articles Section Civil radio communications.

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Comments on the article:

R'RёS,R ° F "RёR№
The text is most likely an error: capacitor C2 is not an element of frequency regulation, according to the scheme it stands as an RF filter. Most likely in the text instead of C2 should be C1.

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