Universal probe. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal probe. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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This relatively simple device has a wide range of capabilities that a radio amateur can use in his practice. The probe allows you to determine the presence of voltage up to 300 V in various circuits of the radio device, "ring" the installation, check the diodes and capacitors, the performance of the cascades of RF and AF amplifiers, triggers, counters, registers.

Universal probe

The basis of the device is a generator (see figure), made on the elements DD1.1, DD1.2. When the SA1 switch is in the position shown in the diagram, the output pulses of the generator follow at a frequency of about 1000 Hz (it depends on the values of the capacitor C2 and the resistor R1). When the switch is set to position "2", pulses follow at intervals of approximately 4 s.

With the SA2 switch, the generator is connected (through inverters DD1.3, DD1.4) to the rest of the device - LED indicators HL1, HL2 and a noise generator (described in detail in the book by V. A. Skrypnik "Devices for monitoring and adjusting amateur radio equipment" .- M .: Patriot, 1990), made on a VD1 zener diode.

Consider the operation of the probe in various modes.

Determining the presence of voltage. Switch SA2 is set to the "Off" position, SA1 can be in any position. A controlled DC voltage exceeding 20 V (but not more than 300 V) is applied to sockets X3 and X6. The current flowing through the circuit resistor R6 - LED - resistors R2, R3 lights up the HL1 LED when a minus voltage is applied to the X3 socket or the HL2 LED if there is a positive voltage on this socket. When testing circuits with alternating voltage, both LEDs flash. When monitoring voltage less than 20 V, sockets X2 and X3 are used.

Checking the RF paths. Switch SA1 is set to position "2" and SA2 is set to "On". The noise generator comes into action, generating a signal with a frequency from units of kilohertz to tens of megahertz. The power of the noise signal is much higher than the power of the receiver's own noise. This allows you to tune the RF circuits of the receiver, focusing on changes in the noise level in the dynamic head.

The source of noise is the Zener diode VD1, operating in the avalanche breakdown mode at a current of about 100 μA. The load of the generator is resistor R5, the signal from which is fed through sockets X5 and X6 to the radio receiver circuit.

Controls the operation of the multivibrator generator on the elements DD1.1, DD1.2. When positive pulses (logic 1) enter the zener diode, it generates noise; in the pauses between pulses (logical 0), the zener diode is turned off. As a result, the noise signal from the generator and the receiver's own noise will alternate at the receiver output. If during the adjustment process there is an increase in the volume of the noise signal compared to its own noise, then the real sensitivity of the receiver increases.

Checking the paths of the AF. Switch SA1 - in position "1", SA2 - "On". A signal with a frequency of about 1 kHz is fed to the controlled device from sockets X4, X6, the signal amplitude is changed by a variable resistor R3.

"Dial" installation. The position of the switches is the same as in the previous case. Probes for checking wiring circuits are connected to sockets X1 and X3. If the circuit under test is OK, both LEDs flash.

Diode test. The position of the switches and the sockets used are the same. Depending on the polarity of the diode connection, either one LED or the other will light up. When the diode is closed, both indicators will flash.

Checking capacitors with a capacity of more than 0,47 uF. The sockets used are the same as the switch positions. When connected to the capacitor sockets, both indicators will light up. Then switch SA1 is moved to position "2". If the capacitor is good, the LEDs will flash alternately. The duration of the flashes depends on the capacitance of the capacitor.

Checking digital devices (triggers, counters, registers). Switch SA2 - in the "On" position. From sockets X1, X6, clock pulses of the generator of the above frequency parameters are fed to the device under test.

In addition to those indicated in the diagram, the microcircuit can be K561LE5, K176LA7, K176LE5, and LEDs - AL307A. It is possible to use other LEDs, but if their direct current is less than 20 mA, then the maximum controlled voltage will decrease by about 20/I pr times. Switches - type P2K with position fixing or any others.

The probe is powered by a Krona battery or another 9 V source, the current consumption does not exceed 6 mA (the highest consumption is in the "ringing" mode).

Oxide-capacitor CMOS oscillators are often unstable. Therefore, it is advisable, by reducing the capacitance of the capacitors C1 and C2 by half (to 2,2 μF and 1300 pF, respectively) and increasing the resistance of the resistor R1 to 1 MΩ, to use the KM-1 capacitor or another specified capacitance as C6.

Author: V.Semenov, Nazyvaevsk, Omsk region

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