An inventor in the field of electrical wire connections, E.I. Gvozdev was actually a successor to G.G. Ignatiev, furthering the work of the military signaller and improving methods of simultaneous telephony and telegraphy. The proceedings of the Russian experts formed the basis for the practical implementation of multiplex communication lines. Thanks to their skill, the operation of genuine long-distance communication began. Great credit for this belongs to the engineer E.I. Gvozdev.
After numerous experiments Gvozdev concluded that, whether for different lines or for the same line, the state of which was influenced by weather conditions or other reasons, it was necessary in each case to include specific capacitors and inductors in the circuit for simultaneous telegraphy and telephony. He therefore proposed, at each station, to place variable capacitance and inductance units and developed parallel and sequental switching systems for various cases.
The engineer Gvozdev also proposed a plan for the dual microphone and telegraphing system. In order to reduce the impact of telegraph pulses on the phone, a device was used for phonic calling so that, unlike inductors, there would be no interference with telegraph devices. For the first time, the structure used a dual carbon microphone with dual differential circuit switching rods with two microphone contacts. Movement of the diaphragm caused an increase in resistance of one contact and a corresponding decrease in the other. A Galvanometer at the top of the apparatus was used to control the telegraph current. Thus, it became possible to send high power signals and also call through the iron wire over a distance of a hundred miles or more, something previously only possible with copper wire.
In 1887, E.I. Gvozdev and engineer Bunge established 'Telephone Partnership'. In 1888-89, at the Rybinsk-Bologovo railway, they conducted successful tests of their devices for simultaneous telegraphy and telephony at a distance of 295 km.
In 1891, the system was applied to the railways. Individual railway sections were equipped with Gvozdev devices: Odessa to Nikolaev (1893), Rostov to Taganrog (1895) and then whole railways: Orel to Vitebsk, Kiev to Voronezh and others.
By January 1896, E.I. Gvozdev had developed a detailed telephonization plan for 12 major cities of the Ryazan region. His premature death, however, put a stop to further construction and his designs for long-distance communication in Russia were shelved.