Loud radio reception. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Loud radio reception. 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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The power of electrical oscillations excited in the radio circuit is very small. It is sufficient only for the operation of such a sensitive device as an electromagnetic telephone. Only in exceptional cases, when the radio station is located close to the place of reception, a loudspeaker can work at the output of the detector receiver. Under normal conditions, loud-speaking reception can only be carried out if the signals of radio stations are amplified. Transistors and vacuum tubes are used for amplification.

There are high frequency amplifiers (UHF) and audio frequency amplifiers (UHF). As the name itself says, the first of the kicks are used to amplify high-frequency oscillations, that is, before they are detected, and the second to amplify audio frequency oscillations, i.e., s. after the detector. If a high-frequency amplifier is connected between the oscillatory circuit and the detector, and an audio frequency amplifier after the detector, then the output element of the receiver can be a loudspeaker.

The block diagram of such a receiver is shown in Fig.1. The functions of the oscillatory circuit, detector and loudspeaker in this receiver are the same as the functions of similar elements of the detector receiver. Only here, after the detector, there are more powerful sound frequency oscillations, which are additionally amplified by an audio frequency amplifier. The result was a radio device that provides loud-speaking reception, including remote broadcasting stations. The sensitivity of such a receiver is many times higher than that of a detector receiver.

Fig.1. Structural diagram of a receiver providing loud radio reception

In the receiver, according to such a block diagram, only one frequency conversion occurs - detection. Before the detector is UHF, and behind the detector is UHF. Receivers in which only frequency conversion occurs are called direct amplification receivers. They are characterized by a formula in which the detector is denoted by the Latin letter V, the number of high-frequency amplification stages is indicated by the number in front of this letter, the number of audio frequency amplification stages is indicated by the number after this letter. So, for example, in the 1-V-1 receiver, in addition to the detector, there is one high-frequency amplification stage and one audio frequency amplification stage.

In simple transistor or tube receivers, there may not be UHF or UHF. And in more complex ones... However, let's not get ahead of ourselves. There will be more discussion about this.

Publication: N. Bolshakov, rf.atnn.ru

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Diagnosis by phone 25.04.2001

25.04.2001
A cell phone signal can be used to determine the pulse and breathing rate of its owner, even if he does not answer calls.

A group of engineers from the American firm "Bell" drew attention to the fact that part of the radio waves emitted by the telephone antenna is reflected from the chest, heart and lungs of its carrier. And since these organs move rhythmically, the frequency of the reflected waves changes accordingly due to the Doppler effect.

These fluctuations are very small - only one billionth part, but they can be caught. Engineers are now going to add a small circuit to the mobile phone that will detect Doppler changes and transmit information about them to the base station, where processing will extract information about the vital signs of the person in whose hand or pocket the phone is located.

To get information about the work of the heart and lungs, just call the device. The Doppler information will be superimposed on the return signal indicating that the called phone is on and ringing. But you can also do this during a conversation - very low frequency signals are easy to filter out from the voice signal.

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