Search

In the current context of global communications, HF (High Frequency) NVIS (Near Vertical Incidence Skywave) data networks can be of strategic importance, providing short- and medium-range communication capabilities independent of terrestrial configuration and existing conventional communications infrastructure. They are essential in critical conditions, such as natural disasters or conflicts, when terrestrial networks are unavailable. This paper investigates the development of such systems for HF NVIS data communications by introducing a customized Orthogonal Frequency Division Multiplexing (OFDM) protocol with parameters adapted to HF ionospheric propagation, implemented on Software-Defined Radio (SDR) systems, which provide extensive configurability and high adaptability to varying HF channel conditions. This work presents an innovative approach to the application of OFDM narrow-channel aggregation in the HF spectrum, a technique that significantly enhances system performance. The aggregation enables a more efficient utilization of the available spectrum and an increase in the data transmission rate, which represents a substantial advancement in NVIS communications. The implementation was realized using an SDR system, which allows flexible integration of the new OFDM protocol and dynamic adaptation of resources. The work also includes the development of a messaging application capable of using this enhanced HF communication system, taking advantage of the new features of channel aggregation and SDR flexibility. This application demonstrates the applicability of the protocol in real-world scenarios and provides a robust platform for data transmission under conditions of limited access to other means of communication. Thus, this study contributes to the technological advancement of NVIS communications and opens new research and deployment directions in HF communications. [ABSTRACT FROM AUTHOR]

Electromagnetic spectrum (EMS) superiority represents a prerequisite for resilient defence strategies, capable of effective and adequate response to our global security environment. Besides, quantum communications are being considered one of the most promising technologies with applications in security related domains. To this extent, the development of quantum communication infrastructures will significantly impact the architecture of the modern electromagnetic operational environment. Quantum technologies pave the way towards revolutionary technologies by exploiting physical phenomena from different angles and enabling extremely sensitive measurements of multiple parameters including electromagnetic fields. This paper aims to present a short description of quantum technologies with applications for electromagnetic spectrum monitoring and discusses their impact on future electromagnetic warfare operations.

By applying a non-standardized methodology and by using electric- and magnetic-field probes of small dimensions (< 1cm), we experimentally characterized the electromagnetic shielding properties of a fabric containing ferromagnetic microwires weaved on a single direction. Electronic microscopy and X-ray spectroscopy revealed the structure, dimensions and chemical elements content of the amorphous magnetic material. Electric shielding factor proved to be very low in the investigated frequency range, but magnetic shielding factor was high, especially when the weaving direction of the magnetic wires corresponded to the polarization direction of the emitting antenna, and showed some resonances. The magnetic shielding efficiency, if checked against an increasing incident magnetic flux density, proved not to change up to 200 nT. The investigated fabric have been previously proved to be very efficient in shielding the field emitted by a mobile phone in its near field, but present results show that near and far field shielding properties are different.