Radio probe. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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This is how we conditionally call this design, which will undoubtedly help in establishing or repairing various radio receiving, amplifying and generating devices and will allow you to check the operation of individual stages by ear.
The probe (Fig. 1) is a broadband radio receiver without tuning elements, with a three-stage radio frequency amplifier. Transistors VT1, VT2 are connected according to a common collector circuit, which provides a sufficiently large input impedance of the amplifier and allows you to connect its input sockets X1 and X2 to the corresponding circuits of the device under test without introducing a noticeable detuning of the circuits. The cascade on the transistor VT3 amplifies the voltage signal.
Fig.1 (click to enlarge)
The RF amplifier transistor mode for DC is set by resistors R1-R6. From the amplifier load - resistor R5 - the signal goes to the detector stage, in which the diode VD1 operates. The audio frequency component of the detected signal is isolated on the resistor R7, after which it is amplified by a cascade on the transistor VT4 - the headphone BF1 serves as its load.
If you need to check the sound path of the radio receiver, electrophone, or control the operation of the AF oscillation generator, the wire with the probe at the end is connected to the X3 or X4 socket. The first of them is designed for a weaker signal, through the second a high-level signal is supplied. For any test, socket X2 is connected to the common wire of the device under test. The probe is powered by a galvanic battery GB1 connected by a SA1 switch.
The details of the probe are placed on a printed circuit board (Fig. 2) made of foil fiberglass or on a plate of ordinary textolite or getinaks.
Ris.2
For the RF amplifier, in addition to those indicated in the diagram, transistors KT361V or MP42B are suitable, any transistor from the MP39-MP41 series works well in the RF amplifier. The detector diode can be any of the D9 series, resistors - MLT, MT with a power of at least 0,125 W, oxide capacitors K50-6 (C5, C6) and KLS (the rest). It is better to take a phone of the TON-2 type, a 3336 battery is suitable as a power source.
After assembling the device and turning on the power, it is useful to check the compliance of the currents of the transistors VT3, VT4 indicated in the diagram. In case of significant differences, the resistor R1 or R8 is selected accordingly.
In conclusion, it should be noted that, if desired, you can expand the functionality of the device: adding a magnetic antenna connected to the RF amplifier with a separate switch will allow you to receive local radio stations. It is clear that in this case it will be necessary to slightly increase the dimensions of the case and the board.
Author: Yu. Prokoptsev
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