Novel method to measure the gain of UHF directional antennas using distance scan

A novel antenna gain measurement method is described which uses power transfer values that are measured while varying the distance between two antennas (Distance Scan). It can be executed with simple means and is cost-effective. The Distance Scan method yields derived free space antenna gain values if a calibrated reference antenna is used and can be combined with the Three Antenna Method to obtain absolute antenna gain values. The method is demonstrated with the antenna gain measurement of three 12 element Yagi-Uda antennas and two 15 element Log-Periodic Dipole Antennas (LPDA's) on 8 frequencies. The measurement results of the LPDA's are compared with values obtained by external calibration, confirming the validity of this method

Multiyear Trans-Horizon Radio Propagation Measurements at 3.5 GHz

The design, realization and measurement results of a high accuracy multiyear 3.5 GHz trans-horizon radio propagation measurement system are discussed, with both emphasis on the results and implemented technical measures to enhance the accuracy and overall reliability of the measurements. The propagation measurements have been performed on two different paths of 253 and 234 km length, using two transmitters and one receiver in the period September 2013 till November 2016. One of the paths travels over wetland, the other path can be considered as a land path. On each path an additional transmitter is placed at 107 km (in the 253 km path) and 84 km (in the 234 km path) from the receiver. With this arrangement, the correlation between two non-aligned paths of comparable length, and two aligned paths of dissimilar length, were studied. The measurements show that for the land path, the predicted ITU-R P.452-16 CDF (Cumulative Distribution Function) typically shows 5 dB higher path loss than the actual measured CDF for the region of interest; anomalous propagation. This means that the measured signal is on average weaker than predicted (a higher path loss). For the wetland path the actual CDF is very close to the predicted CDF. Also, the measurements reveal that typically 30% of the anomalous propagation occurrences are correlated with other paths

STARD 2015: An Updated List of Essential Items for Reporting Diagnostic Accuracy Studies.

Incomplete reporting has been identified as a major source of avoidable waste in biomedical research. Essential information is often not provided in study reports, impeding the identification, critical appraisal, and replication of studies. To improve the quality of reporting of diagnostic accuracy studies, the Standards for Reporting of Diagnostic Accuracy Studies (STARD) statement was developed. Here we present STARD 2015, an updated list of 30 essential items that should be included in every report of a diagnostic accuracy study. This update incorporates recent evidence about sources of bias and variability in diagnostic accuracy and is intended to facilitate the use of STARD. As such, STARD 2015 may help to improve completeness and transparency in reporting of diagnostic accuracy studies

NVIS-elevatiehoekmetingen = Mesures d’angles d’élévation NVIS

Near Vertical Incident Skywave propagatie, of NVIS, krijgt de laatste tijd veel aandacht. Dat is niet verbazingwekkend, want dit propagatiemechanisme is bijzonder geschikt voor HF noodverkeer. Met NVIS kan een gebied met een straal van een paar honderd kilometers worden bestreken met uitstekende signalen, zelfs wanneer een gemiddeld zendstation wordt gebruikt. Er zijn echter vrijwel geen meetgegevens beschikbaar die theorieën met betrekking tot dit fenomeen bevestigen. Aujourd’hui le principe “NVIS” reçoit beaucoup d’attention. Rien d’étonnant puisque ce mécanisme de propagation intervient dans nombre de cas de communication d’urgences en HF. Avec NVIS, un rayon de quelques centaines de km peut être couvert avec des très bons signaux, même en utilisant une station émettrice ‘’ordinaire’’. Néanmoins il existe peu d’informations expérimentales pour supporter des théories sur ce phénomène. Quelques radioamateurs Néerlandais décidèrent d’y remédier. Les résultats et conclusions de cette expérimentation sont présentés ici

Novel method to measure the gain of UHF directional antennas using distance scan

A novel antenna gain measurement method is described which uses power transfer values that are measured while varying the distance between two antennas (Distance Scan). It can be executed with simple means and is cost-effective. The Distance Scan method yields derived free space antenna gain values if a calibrated reference antenna is used and can be combined with the Three Antenna Method to obtain absolute antenna gain values. The method is demonstrated with the antenna gain measurement of three 12 element Yagi-Uda antennas and two 15 element Log-Periodic Dipole Antennas (LPDA's) on 8 frequencies. The measurement results of the LPDA's are compared with values obtained by external calibration, confirming the validity of this method

Influence of Controlled and Uncontrolled Interventions on Twitter in Different Target Groups

Abstract—In this paper the influence of interventions on Twitter users is studied. We define influence in a) number of participants, b) size of the audience, c) amount of activity, and d) reach. Influence is studied for four different target groups: a) politicians, b) journalists, c) employees and d) the general public. Furthermore, two types of interventions are studied: a) by all Twitter users (i.e., uncontrolled interventions), and b) those tweeted by an organization that benefits from any resulting influence (i.e., controlled interventions). As a case study, tweets about a large Dutch governmental organization are used. Results show a clear relation between the number of uncontrolled interventions and influence in all four target groups, for each of the defined types of influence. Controlled interventions show less influence: Significant influence was found for the general public, but influence for politicians and employees was only mildly significant, and no influence was found for journalists. The effect found for uncontrolled interventions however suggests that this influence is indeed reachable for some target groups, even when the number of interventions is small, and very well reachable for all target groups, provided the number of interventions is large enough. In addition to this we found that interventions influence groups to a different extent. Own employees were influenced strongest, differing significantly from the other groups

Free-energy minimization in joint agent-environment systems: A niche construction perspective

The free-energy principle is an attempt to explain the structure of the agent and its brain, starting from the fact that an agent exists (Friston and Stephan, 2007; Friston et al., 2010). More specifically, it can be regarded as a systematic attempt to understand the 'fit' between an embodied agent and its niche, where the quantity of free-energy is a measure for the 'misfit' or disattunement (Bruineberg and Rietveld, 2014) between agent and environment. This paper offers a proof-of-principle simulation of niche construction under the free-energy principle. Agent-centered treatments have so far failed to address situations where environments change alongside agents, often due to the action of agents themselves. The key point of this paper is that the minimum of free-energy is not at a point in which the agent is maximally adapted to the statistics of a static environment, but can better be conceptualized an attracting manifold within the joint agent-environment state-space as a whole, which the system tends toward through mutual interaction. We will provide a general introduction to active inference and the free-energy principle. Using Markov Decision Processes (MDPs), we then describe a canonical generative model and the ensuing update equations that minimize free-energy. We then apply these equations to simulations of foraging in an environment; in which an agent learns the most efficient path to a pre-specified location. In some of those simulations, unbeknownst to the agent, the 'desire paths' emerge as a function of the activity of the agent (i.e. niche construction occurs). We will show how, depending on the relative inertia of the environment and agent, the joint agent-environment system moves to different attracting sets of jointly minimized free-energy

Design and validation of probes and sensors for the characterization of magneto-ionic radio wave propagation on Near Vertical Incidence Skywave paths

his article describes the design and validation of deployable low-power probes and sensors to investigate the influence of the ionosphere and the Earth’s magnetic field on radio wave propagation below the plasma frequency of the ionosphere, known as Near Vertical Incidence Skywave (NVIS) propagation. The propagation of waves that are bent downward by the ionosphere is dominated by a bi-refractive mechanism called ‘magneto-ionic propagation’. The polarization of both downward waves depends on the spatial angle between the Earth’s magnetic field and the direction of propagation of the radio wave. The probes and sensors described in this article are needed to simultaneously investigate signal fading and polarization dynamics on six radio wave propagation paths. The 1-Watt probes realize a 57 dB signal-to-noise ratio. The probe polarization is controlled using direct digital synthesis and the cross-polarization is 25–35 dB. The intermodulation-free dynamic range of the sensor exceeds 100 dB. Measurement speed is 3000 samples/second. This publication covers design, practical realization and deployment issues. Research performed with these devices will be shared in subsequent publications