Probe-generator for testing radio equipment. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The radio receiving paths of various equipment (radios, radios, CB transceivers, etc.) contain such similar nodes as audio frequency amplifiers (3CH), intermediate frequency amplifiers (IF) of FM and AM stations. They have to be checked when repairing equipment in the first place. The probe generator proposed here will help with this.

This relatively simple instrument generates 3 kHz 1CH pilot signals and 10,7 MHz and 465 (or 455) kHz modulated IF signals. The amplitude of each signal can be smoothly adjusted.

The basis of the device (Fig. 1) is a generator based on a transistor VT1. Its operating modes are set by the switch SA1. In the position shown in the diagram ("3H") of the switch, the supply voltage of the battery GB1 is supplied through the resistor R9 to the transistor and the generator starts to operate at a low frequency. It is determined by the frequency setting circuit R2C3R3C4R5C5 in the transistor feedback circuit.

In the switch position "465", the supply voltage to the transistor is supplied through the resistor R10, while the VD1 diode opens and the ZQ1 filter is turned on in the feedback circuit of the transistor stage. 3H (1kHz) and AM IF (approximately 465kHz) are generated, while the IF signal is modulated by the 3H signal. Filter R1C1 eliminates high frequency feedback through capacitors C3-C5, ensuring stable operation of the oscillator at the IF.

When the switch is set to the "10,7" position, the supply voltage to the transistor is supplied through the resistor R11. The VD2 diode opens, and the ZQ2 filter is included in the feedback circuit. The generator will operate at 3H (1 kHz) and IF FM (approximately 10,7 MHz). The IF signal is modulated with a 3H signal.

The generated signals through the resistor R12 and the capacitor C8 are fed to the output voltage regulator R13, and from its engine to the output sockets X1 and X2.

In the switch position "Off." the power supply is disconnected from the generator.

In addition to that indicated in the diagram, transistors KT3102A-KT3102D, KT312V can be used in the device. ZQ1 filter - any of the FP1P-60 series, narrower band is better. At a frequency of 455 kHz, a foreign-made filter should be used. The ZQ2 filter is a bandpass piezoceramic filter at a frequency of 10,7 MHz, domestic (for example, FP1P-0,49a) or similar imported. Capacitors - K10-7, K10-17, KLS or small imported ones. Trimmer resistor R2 - SPZ-1b, variable R13 - SPO, SP4, the rest - MLT, S2-33. Switch - any small-sized switch for one direction and four (or more) positions. Power source - voltage 4,5 ... 12 V. These can be series-connected galvanic cells, batteries, a Krona battery, or a source of a tested design.

Most of the parts are placed on a printed circuit board (Fig. 2) made of one-sided foil fiberglass.

It is placed in a plastic case of a suitable size, on which a variable resistor R13 is installed, sockets X1, X2 (Fig. 3).

A probe is inserted into one of the sockets, depending on which nodes are being checked. The common wire is led out through a hole in the housing and is provided with a crocodile clip. In the case when the power supply is built-in, it is necessary to provide a place for it in the case. The installation of capacitors C7, C9, C10 is carried out by the method of surface mounting.

Instead of a filter at a frequency of 465 kHz, you can put a filter at 455 kHz - then the generator will operate at this frequency. It is permissible to use a five-position switch and enter this frequency additionally. The new filter must be enabled in the same way as the ZQ1. If external power is planned, a new frequency can be set using the released switch contact.

You need to configure the device at the voltage with which it will work. Current consumption - within 0,5 ... 3 mA, depending on the supply voltage.

Establishing a probe-generator begins with determining the mode for direct current. To do this, in the switch position "10,7" and the lower position of the resistor R2 engine according to the diagram, by selecting R6, approximately half of the supply voltage is set on the collector of the transistor. In the event of generation at a frequency significantly below 10,7 MHz (on parasitic filter transmission channels), the capacitance of capacitor C6 must be reduced. If there is no generation at all, then the capacitance of this capacitor and the resistance of the resistor R7 should be increased. Generation is controlled using an oscilloscope (or frequency meter) by connecting it to a common wire and the corresponding socket.

Then, the generation is checked in the switch position "465" (or "455") and by moving the slider of the resistor R2, stable generation of 3H and IF signals is achieved at the switch positions "465" ("455") and "10,7". If the generation is unstable in the "3H" position, you will have to select the resistor R9.

The probe is used as usual, applying signals to certain points of the device under test.

Author: I. Nechaev, Kursk

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