## 1 Introduction  
The concept of the Internet of Things (IoT) covers communications in distributed energy production facilities, known as smart grids [1, 2]. Communications for transmitting command and control information in smart grid energy facilities should often cover long ranges. As an example, off-shore power plants are often outside of the service area of mobile networks [3], and satellite communications would be too expensive. Additionally, point-to-point communications are always preferred for transmitting controls and commands compared to any other third-party solutions. Point-to-point solutions in UHF such as LoRa might not be reliable enough, especially in the offshore environment. Low-power and low-rate HF communication systems [4, 5] can be easily implemented and made extremely reliable for transmitting information through appropriate signal processing [4, 6] and appropriate frequency management [7, 8, 4]. Such communications are not only immune to noise, as they usually operate at a negative signal-to-noise ratio, but they also do not interfere with other communication services due to their extremely low power. Moreover, techniques mainly used for higher frequency ranges such as spread-spectrum [9] or ultra-wide band technologies [10] could be implemented on a fully software-defined radio platform [11, 12, 13], and can further reduce the risk of interference with other HF communication systems or between components of the same communication system. Sensor networks in the HF band have successfully been implemented, e.g., for biological and geophysical monitoring in remote places [14], covering either short ranges of approximately 250 km, or transequatorial ranges of more than 10,000 km. In distributed energy production facilities, communication ranges are usually in the order of 100 km. Antennas transmitting controls and commands over HF should therefore provide communications at a high elevation angle, i.e., over a short skip. They also have to operate over a wide frequency range, so as to constantly adapt the frequency to the current propagation conditions. Antenna structures should also be low-cost and low-profile, e.g., traveling wave linear wire antennas. The radiation pattern of an HF antenna is highly impacted by the environing objects. In order to provide reliable communications over the entire frequency range of interest between two sites of the grid, the HF antennas should be measured in situ [15; 16; 17], making therefore sure that the main lobe direction is pointing to the correspondent site. Advancements in GPS accuracy, miniaturization of the data acquisition and processing systems, development of the real-time data communication systems, improvements in autonomous flight capabilities and battery life make drone-borne systems a viable solution for accurate HF antenna measurements. Recently, many drone-borne antenna-measuring systems have been developed as drones have become more and more affordable. However, most of those solutions were developed for frequencies above the HF band [17; 18; 19; 20; 21; 22; 23], and very few for HF antennas [24; 25]. In this work, we propose a drone-borne data-acquisition system using a short, folded dipole as a probe antenna. The measurements are performed by flying the drone carrying the probe at a distance in the order of one meter along the HF antenna under test, so as to provide a safe flight and a low risk of interference between the transmitted signal and the drone control circuitry. It should be emphasized that near-field to far-field transforms must be performed when measuring an HF antenna with such a drone-borne system [26; 27]. A calibration procedure to take into account the effect of the field zone, ground reflection, and drone chassis is also presented. High-frequency communications in smart grid facilities should utilize most of the frequency range to keep a reliable link, regardless of the season or time.