A device for tuning radio equipment. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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This device contains three main nodes. IF signal generator 465 kHz, modulated by a low-frequency signal with a frequency of 1 kHz; a transistor tester with an assessment of their transfer coefficient (in this case, it is possible to perform a test without desoldering transistors from the circuit); tester of transformers for the absence of interturn short circuits.
(click to enlarge)
The first node is made in the form of a low-frequency LC oscillator with an analog of a lambda diode and a modulated LC oscillator. The node is operational in the power supply voltage range from 0,32 to 4,2 V. At its output, there is simultaneously a low-frequency signal of 1 kHz and a signal modulated by this frequency of 465 kHz. The amplitude of the total output signal is 80 mV.
The second node is made according to the scheme of a blocking generator, the active element of which is the tested transistor. Generation control is carried out on the head phone. The transfer coefficient values for germanium and silicon transistors are marked on the limb of the resistor R3.
The third node is structurally similar to the second and consists of a transistor and positive feedback circuits formed by the transformer under test. An ohmmeter is connected to the "x1" terminals and, by switching the toggle switch Ш, the suitability of the transformer is determined by the difference in the readings of the ohmmeter (and by sound indication), and in the absence of these signs, the presence of short-circuited turns in it.
As a transformer Tp1, a transformer of a vertical scanner of a television receiver (or another similar one) can be used. The circuit L1C5 is the oscillatory circuit of the intermediate frequency filter of the radio receiver. As Tr2, a transformer with a transformation ratio of 7:1 - 20:1 is used, and the capacitance of the capacitor C4 must be selected so that the generation frequency is 1 kHz. Switch Ш is also the switch of the device.
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