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Noise Detector (ART493E)

Capture a broad spectrum of ambient electromagnetic noises for application in measurement instruments or simple evaluation by listening. The complete circuit is given in figure 1.


Figure 1 - Detector diagram
Figure 1 - Detector diagram




• Determination of the noise level in a factory or other location where noisy machines and electronic devices operate.

• Assessment of the level of interference in locations where sensitive equipment or even household appliances subject to interference are to be installed.

• Determination of the intensity of noise produced by an industrial machine or a circuit.

• Survey of the noise spectrum of a site or produced by a machine with the help of the spectrum analyzer.


Constructive Details:

The circuit consists of an aperiodic radio receiver, that is, without tuning, capable of covering a frequency range that goes from a few tens of kilohertz to more than 5 Megahertz. We can connect it directly to an audio amplifier to hear these signals, connect it to a sensitive indicator instrument (AC voltmeter) or to the input of a spectrum analyzer.

The printed circuit board is shown in Figure 2. The RF shock is formed by 400 turns of fine enameled wire (30 or 32 AWG) in a ferrite rod of 0.5 to 1 cm in diameter and up to 10 cm in length.

The consumption of the circuit is very low, and for greater sensitivity a germanium diode must be used. The antenna, which is optional, is telescopic type up to 1 m in length.


Figure 2 - Printed circuit board for the detector
Figure 2 - Printed circuit board for the detector




Q1 - BF494 or equivalent - RF transistor

D1 - 1N34 or equivalent - any germanium diode


Resistors: (1/8 W, 5%)

R1 - 470 k ohm

R2 - 10 k ohm



C1 - 22 nF - ceramic

C2-47 nF - ceramic



B1 - 3V - 2 small batteries

XRF1 - View text

A - telescopic antenna

Printed circuit board, battery holder, output cable, printed circuit board, wires, solder.