Detector and detection. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Detector and detection. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In your first receiver, a dot diode acted as a detector. I will tell you in detail about its structure and work in the fifth conversation. Now I’ll just say that it is a two-electrode semiconductor device with one-sided current conductivity: it passes current through itself well in one direction and badly - current in the opposite direction. To simplify the explanation of the operation of the diode as a detector, we will assume that it does not conduct the reverse current at all and is, as it were, an insulator for it. This property of the diode is illustrated by the graphs shown in Fig. 1: diode D passes positive half-waves through itself and does not pass negative half-waves of alternating current at all. The negative half-waves of the diode, as it were, cut off. As a result of this action of the diode, the alternating current is converted into a pulsating current - a current of one direction, but changing in magnitude with the frequency of the current passed through it. This conversion process, called AC rectification, is the basis of radio signal detection.

Detector and detection
Fig.1. Diode converts alternating current into pulsating current

Look at the graphs shown in Figure 2. They illustrate the processes taking place in the familiar detector circuit of the simplest reception-peak. Under the action of radio waves, modulated high-frequency oscillations are excited in the receiver circuit (Fig. 2a). A circuit is connected to the circuit, consisting of a diode and telephones. For this circuit, the oscillatory circuit is a source of high frequency alternating current. Since the diode passes current in only one direction, high-frequency oscillations entering its circuit will be rectified by it (Fig. 2, b), or, in other words, detected. If you draw a dashed line around the peaks of the rectified current, you get a "pattern" of the audio frequency current, which modulated the current in the radio station antenna during transmission.

Detector and detection
Fig.2. Graphs illustrating the detection of high frequency modulated oscillations.

The current obtained as a result of detection consists of high-frequency pulses, the amplitudes of which change with the sound frequency. It can be considered as a total current and decomposed into two components: high-frequency and low-frequency. They are called, respectively, the high-frequency and low-frequency components of the pulsating current. The low-frequency component goes through the phones and is converted by them into sound.

Publication: N. Bolshakov, rf.atnn.ru

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