Noise generator - probe. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Noise generator - 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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You can tune a sensitive amplifier or receiver using a noise generator - a device that generates oscillations in a very wide frequency spectrum, up to hundreds of megahertz.

A diagram of a simple noise generator made on a D810 zener diode (D808, D814A-D814G can be used) is shown in fig. 1. The generator mode is set by a variable resistor R1.

Noise Generator - Probe
Fig. 1

The output of the noise generator is connected to the input of the low-frequency amplifier under test, radio receiver, tape recorder or other radio engineering device. During normal operation of the device, a characteristic hissing sound will be heard in its loudspeaker.

By applying the signal of the noise generator to the input of the superheterodyne, it is possible to match its contours. When tuning a receiver with extended ranges, it is sufficient to pair the contours only at the middle point of the range: the receiver is tuned to the middle frequency of the range and the maximum noise level at its output is achieved. On survey ranges, conjugate contours are produced at the two extreme points of each range. In the short-wave part of the range, tuning is done by changing the capacitance of the input circuit, in the long-wave part - by changing the inductance of the input circuit.

Based on the noise generator, you can build a signal generator, the circuit of which is shown in Fig. 2. The entire frequency range of the generator 100 kHz - 27 MHz is divided into five subranges: 100-300 kHz, 300 kHz - 1 MHz, 1-3 MHz, 3-9 MHz, 9-27 MHz. The maximum voltage at the output of the generator is a few millivolts.

Noise Generator - Probe
Fig. 2

Coils L1 - L5, together with a variable capacitor C3, form oscillatory circuits that highlight the frequencies that can be obtained at the output of the generator.

The generator coils are wound on frames with a diameter of 7,5 mm with SCR-1 tuning cores (used in TV IF amplifiers). The winding data of the coils are shown in the table.

Coils	Number of turns	The wire
L1	270 + 270	PELSHO 0.1
L2	260	PELSHO 0,12
L3	80	PELSHO 0,12
L4	30	PEV-1 0,2
L5	10	PEV-1 0,2

Coils L1 - L3 are wound in bulk, winding width 7 mm; coils L4 and L5 - in one layer, turn to turn. The variable capacitor can be of any type.

Set up the generator with the power off. The output of the generator is connected to the output of the reference GSS, and a lamp voltmeter is connected in parallel with the circuit. According to the maximum reading of the voltmeter, which will correspond to the resonant frequency of the circuit, the required subrange boundaries are selected and the generator scale is calibrated. Similarly adjust the contours of other subranges.

The principle of tuning receivers using the generator described here is the same as with the GSS. When tuning the circuits to certain frequencies, the signal is supplied from the "Output 1" terminal of the generator, and when pairing the circuits, from the "Output 2" terminal.

Author: N. Zudov; Publication: N. Bolshakov, rf.atnn.ru

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