The technology of frequency coding in channels of quantum key distribution allows to determine the ground state of photons through the value of the amplitude of its carrier, frequency modulated in phase (PM) or amplitude (AM) by a radio-frequency signal, and the resulting side components. Over the past twenty years, it has been substantially modified and improved. At the same time, in recent works, an expanded understanding of the frequency coding principle is used, in which each photon state is associated not with the phase of the modulating signal at a certain frequency, but with one or more sideband frequencies or the carrier frequency of the photon itself. In this paper, we present the results of constructing a frequency coding system of quantum key distribution (QKD) based on the serial electro-optical photon amplitude modulation and phase commutation. The possibility of reducing the probability of achieving a positive result in PNS attacks by Eva is shown by eliminating the carrier of the signal transmitted via the quantum channel from the structure of the key distribution. It was early noted, that the smallest value of QBER is achieved in schemes with a passive definition of one or two basic states of a photon, i.e. without the use of remodulation processes, that is realized in considering. Additionally it is not necessary to form a notch filter system, which is usually carried out using fiber Bragg gratings (FBG) or arrayed waveguide gratings (AWG) for discrimination the photon carrier and its sideband components.