Index Prof. graph Ham graph

Elevation angles (Published Electron # 10, 1988) Introduction Electron-magazine has published in 1988 a series of four translated articles on propagation from "Neues von Rohde & Schwarz" dating from 1986 by Axel Stark. This interesting information proved to be very useful for our radio-communication hobby. I often have relied on this information when designing transmitting and receiving antenna's, especially using the illustrative graphs. Therefore I think this information to also be an indispensable part of this web-site. Reception probability Almost from the very beginning of the radio-era, the Rohde & Schwarz company has been very active in this field, not in the least as a manufacturer of broadcast stations and accompanying antenna farms. To keep track of the efficiency of these antenna systems and related power requirements for the broadcast stations many measurements have been performed and are still continuing to optimize the knowledge on propagation and conditions over time, seasons and years. Many institutes and universities have been studying propagation over the years and from such continuous investigations also various calculating programs have been developed, one of these by the Ionosphere research group of the "Deutsche Bundespost", this in turn being calibrated with data gathering as mentioned. Using this program, the probability may be calculated that a certain radio signal may reach our antenna, related to the elevation angle and frequency. The graphs in figure 1 are an illustration of such calculations, here displaying reception probabilities for stations at around 1500 km. distance, around DX-conditions at the HF amateur radio bands. Figure 1: Probability of arrival re frequency How to use this graph Imagine one wants to know what type of antenna to employ for long distance communications at 10 MHz. In figure 1 we find that signals from a distance of 1500 Km. will arrive 90 % of the time at an elevation angle < 37 degree, for 50 % of the time at an angle below 18 degree and for 10 % of the time below 8 degree. The best antenna for this type of communication than has a main radiation lobe at 37 degree and 3 dB beam width points at 8 respectivily 37 degree w.r.t. the horizon. In further articles on HF antenna's I refer to the area between 90 % and 10 % probability of reception as 'the optimal DX angle'. When testing this, the R&S figures have proven to be a very reliable source and antennas design to these figures have never failed to fulfill expectations. Radio-amateur measurements In the second half of last century, a number of English radio-hams also have performed series of measurements to determine to optimal angle of reception for communication with the VS. These measurements have been carried out of a smaller number of frequencies, over a more limited period, but appear to comply nicely with R&S measurements and the Deutsche Bundespost graphs. Results of these measurements may be found in figure 2. Figure 2: Minimum take-off angle for DX traffic between England and the USA Bob J. van Donselaar, on9cvd@veron.nl