TONE SYSTEM

OM100Tón Systém – ako to fungovalo: During several interviews with radio amateurs, I encountered the question: How did it actually work, that "Tón system"? That's why I decided to write this post.

In fig. 1 is the original patent document with a drawing of both the receiver and the transmitter. First, let's explain the transmitter. This consisted of a battery D, a high-voltage transformer K, a key a, two electrolytic breakers and a spark gap formed by two balls S and B. If we consider only one breaker, we arrive at a classic spark transmitter. By interrupting the current in the primary circuit p of the transformer K, a high voltage is induced in the secondary winding c, which causes a spark jump in the spark gap. This spark causes damped oscillations in the antenna circuit. The resonant frequency of the antenna circuit is determined by the inductance of the secondary winding of the transformer and the capacitances of the spark gap and the antenna conductor. Considering the high inductance, the resonant frequencies were in the range of tens to hundreds of kHz. The rhythm of interruption of the primary circuit caused modulation of the radiated signal. Murgaš used this in his Tón system by using two interrupters with different interrupting frequencies. In doing so, he created a system with two tones of the same length, which replaced the dot and dash in Morse code. With this, he was able to reduce the broadcast time to approximately one third. The advantage of such a circuit breaker was that there was no burning of the contacts, but the disadvantage was a relatively large voltage drop. In the trial version, with a voltage on the transformer primary of 24 V and a current of 5 A, the loss was about 30 V. That is, more than half of the supply voltage.

The function of the electrolytic circuit breaker is explained in fig. 2. This interrupter consisted of two electrodes separated by a glass cup in which there is a small hole. The conductive connection between the electrodes was provided by the electrolyte. When a high-intensity current flows through the electrolyte, it heats up in the opening of the cup and a gas bubble forms, which interrupts the flow of electric current. With a larger opening, the interruption frequency was lower.

A more complicated case is the receiver in fig. 3. From today's electrical engineering, we can only find a battery and a handset in it. The detector was mechanical, powered by a clockwork. The sensitivity of the detector depended on the pressure setting between the contact pen and the carbon rotary contact. The principle of such a detector consisted in reducing the transition resistance between these contacts under the influence of the supplied pulse from the antenna. The quality of the detector was determined by the uniformity of the pressure between the rotary contact and the steel pen. When I built such a receiver, I was interested in sensitivity. I tried to measure it at a frequency of 100 kHz, below that my generator no longer works. It was "amazing" for a signal-to-noise ratio of 6 dB was 50 mV, which is 5 times more than S9 + 40 dB according to the current S scale. A crystal without a low-frequency amplifier for the same signal-to-noise ratio needed 15 mV.

I hope this article helped to understand the difficult beginnings of radio pioneers. But, while they were struggling with the low sensitivity of the receivers, and we, in turn, were dealing with a lot of "weight loss" disorders, regulations and similar pleasures of life.

So YOU ​​73 Miro OM3CKU