What is a Pupin coil and where was it used

Hello dear subscribers and guests of my channel! In this material, I want to tell you about an almost forgotten device that was previously actively used to provide telephone communications. This is Pupin's coil. Interesting? Let's start then.

History of creation

At the very beginning of the development of telephone communication, the following situation arose: telephone communication was simply impossible at significant distances, and all because the electrical signal was severely distorted due to the presence of distributed inductance at the stretched wires and distributed capacitance between them.

For the transmission of telegraph messages using Morse code, the signals are not endowed with important components in the frequency range above 100 Hz. But in order to transmit human speech, it is necessary to use a range of thousands of hertz.

W. G. Pierce, a technician at the British General Post in 1887, compiled his own equation for calculating the maximum length of a telephone line without distortion. Its formula took into account such parameters as: total and specific resistance, length, capacitance and other parameters of the circuit and its configuration.

But despite the constant modernization of the equation, it turned out to be unable to describe real lines.

So vivid proof of this was the Boston-Chicago line of communication, which, according to the equation, simply could not work, although the connection was excellent.

An ardent opponent of Pierce was Heaviside, who openly entered into a stinging squabble with him in the pages of Electrician magazine. He proposed a radically different solution to the problem of limited communication lines.

He suggested not decreasing, but rather increasing the capacity by introducing special inductors. But knowing that Pierce has the exclusive right to impose a moratorium on all proposals in the Office, he did not even try to implement his invention.

And now, 10 years after the first discovery, a similar solution was proposed by a professor at Columbia University M. Pupin. The Serbian scientist also received a patent for "his" invention.

That is why this coil began to be called "Pupin Coil", and the installation of such installations on the line began to be called "Pupinization".

How does the Pupin coil work

M. Pupin proposed to build in the line coils with inductance that exceeds its own line inductance by almost two orders of magnitude, and thereby significantly reduce attenuation in the range frequencies up to 3 kHz.

At the same time, the optimal distance through which such coils were placed was also calculated, and this interval even received its own name "pupinization step". Indeed, as a result of such modernization, the signal transmission in the frequency range from 0.3 kHz before 3.4 kHz.

But this was not without negative aspects. Such a coil greatly degraded the signal transmission at high frequencies, practically turning into a filter for them. Therefore, wherever technology is used on telephone lines DSL and ISDN it is unacceptable to use such coils.

Such coils were actively used (and are still in use) in the US local telephone networks, but in Russia, pupinization was used very rarely.

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