The first radio had a very simple device: a battery, an electric bell, an electromagnetic relay, and a coherer (from the Latin word cogerentia – clutch). This device is a glass tube with two electrodes. The tube contains small metal filings. The operation of the device is based on the effect of electrical discharges on metal powders. Under normal conditions, the coherer has great resistance, since the sawdust has poor contact with each other. The incoming electromagnetic wave creates an alternating current of high frequency in the coherer. The smallest sparks slip between the sawdust, which sinter the sawdust. As a result, the coherer resistance drops sharply (in A.S. Popov’s experiments, from 100,000 to 1000 – 500 Ohm, that is, by a factor of 100-200). You can return high resistance to the device again by shaking it. To ensure automatic reception, it is necessary for wireless communication, A.S. Popov used a ringing device to shake the coherer after receiving the signal. Under the action of radio waves received by the antenna, the metal filings in the coherer interlocked, and it began to transmit electric current from the battery. The relay worked, turning on the bell, and the coherer received a “light shake”, the coherence between the metal filings in the coherer weakened, and the next signal was received.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.