Amateur Radio Propagation Studies
Science, research, engineering, operating
Radio amateurs not only explore radiowave propagation within the Earth atmosphere but also in space by using the moon as a passive reflector which enables VHF, UHF and SHF radio links across the continents. The so-called moonbounce and EME (earth-moon-earth) QSOs represent the most challenging propagation mode in ham radio involving high sophisticated and optimized radio stations. There are even more astronomical bodies playing an important role in VHF communication: meteors entering the Earth atmosphere create short-lived trails of ionized gas in a height of 100 kilometers which we all know as shooting stars. However, this trails may also scatter VHF radiowaves with high efficiency. In the so-called meteor scatter (MS) communication, radio amateurs are managing long distance radio links in 50 and 144 MHz. Finally it is worth to mention that even small ham radio antennas may detect radio signals from outer space, e.g. the radio noise originating from the sun and also from the center of our galaxy.
The US Naval Space Surveillance Mission (NAVSPASUR) detects, identifies and tracks all man-made objects orbiting around the Earth. A multi-static radar system employs fan-shaped radar beams forming a radar fence across the Unites States. These radars operate several thousands of dipol antennas, each dipole is driven by an individual 300 watts transmitter which results in an enormous effective radiated power on 216 MHz. Evidently, this radar can generate strong moon echoes ...
The 'radio moon' on one hand and the visible lunar disk on the other hand, may show very different scattering properties. In fact, in the 1950s it has been discovered that radiowaves, unlike light and infrared radiation, are reflected back to the Earth principally from a small region at the center of the visible disk, i.e. the moon shows a limb darkening at radio wavelengths which does not exist at optical wavelengths. The below paper identifies the scattering area on the lunar surface, discusses the moon's echo depth and speculates about monthly variations in the echo power.
Die ersten Radarechos vom Mond wurden 1946 von Dewitt und Stodola beobachtet, im wissenschaftliche Interesse standen Mondechos jedoch vor allem in den sechziger Jahren. Zur Vorbereitung der Mondlandung erhoffte man durch Radarmethoden Aufschluß über die Oberflächen- und Materialbeschaffenheit des Erdtrabanten zu gewinnen. Die Mondsonden und bemannten Weltraumflüge der Apollomissionen sowie die Verfügbarkeit von Kommunikationssatelliten haben das funktechnische Interesse am Mond jedoch geringer werden lassen. Heute wird der Mond zu Mess- oder Kalibrationszwecken verwendet und die Geodäsie nutzt die von den Apollomissionen 11, 14 und 15 ausgesetzten Laserreflektoren für Entfernungsmessungen. Funkamateure nutzen den Mond seit mehreren Jahrzehnten als passiven Reflektor, um interkontinentale Funkverbindungen im VHF-/UHF-/SHF-Bereich zu verwirklichen. Der nachfolgende Aufsatz diskutiert die physikalischen Grundlagen von Erde-Mond-Erde-Verbindungen (EME).
[August 2005]. Shooting stars and typical meteor scatter bursts are associated with meteorites measured in milligrams. The optical effect therefore fades away in a split second and the scattered radio signals generally disappear after one or two seconds, or so. The photograph on the right shows a very different meteor trail taken 45 minutes after the flash of the meteor that plunged into the Earth atmosphere on January 18, 2000. The image was taken from the space.com website where you may find even more impressive pictures of the Yukon meteor flash. A couple of days later, NASA's Airborne Sciences ER2 plane has still collected samples of the meteor's debrits at an altitude of 19.5 kilometers. My question is: are there any ham reports of unusual VHF long-distance communication in Canada and in the northern U.S. around January 18, 2000? On March 26, 2003 residents in the Chicago area have reported another dramatic encounter with objects from outer space, i.e. a meteor shower rocking on Midwestern homes. A resident reports: "The sky lit up completely from horizon to horizon. A minute or so later the house started rumbling and we heard all these tiny particles hitting the house." This rain of meteorites has finally damaged at least six houses and three cars. Now, do you still feel safe when working on meteor scatter in your ham shack?
[February 2005]. Forecasting the exact time and magnitude of meteor showers is indeed quite a complicated science. Radio amateurs interested in the prediction and observation methods are requested to refer to, e.g., the web site of the International Meteor Organization (IMO). Calculating the variability of meteor activity from one year to another is already difficult, calculating meteor shower activity in, say 2020 or even 2030 must be considered scientific wizardry. The calculation accuracy is difficult to judge but, nevertheless, meteor scientists can provide an interesting outlook. The privately owned CBA Belgium Observatory has compiled the following overview of possible future meteor storms: Alpha Monocerotids in November this year, the Alpha Aurigids in 2007, the Draconids (Giacobinids) in October 2018 and also the comet 73P/Schwassmann-Wachmann3 may generate strong meteor activity in 2022. Esko Lyytinen predicts, in particular, an extraordinary high outburst of the Perseids on August 12, 2028 ... at 05:30 UT by the way - oops.
Die Vorausberechnung von Meteorschauern und ihre Auswirkungen auf Meteorscatter Verbindungen im UKW-Bereich ist eine durchaus anspruchsvolle Aufgabenstellung. Der Autor versuchte sein Glück bei den Perseiden im Jahre 1981: die Schauerprognose war zwar nicht ganz mißlungen, ein Erfolg war es aber dennoch nicht. Das nachfolgende Dokument hat eher historische denn inhaltliche Bedeutung.
Detecting lunar radio echoes is one issue, what about Mercury, Venus and Mars? We may consider moonbounce communication the radio amateur's simple counterpart to scientific radar experiments detecting radio echoes from the planets. However, by using the powerful transmitter of the Goldstone Solar System Radar and by using the Very Large Array as the receiver, the radio astronomer's experimental setup exceeds our capabilities by many orders, of course. Sophisticated instrumentation isn't the only difference though ...
Before launchings research campaigns and before financing the instrumentation and the experimental setup, scientists develop theoretical models to analyse the scientific requirements, benefits and, most important, to analyse what information may be actually expected in an experiment the same was true with the solar radar experiments which were carried out with the El Campo solar radar in the 1960s (38.25 MHz, 500 kW, phased array of 18.000 square meters). However, the observations of that radar "were a surprise in every respect". The echo strength was weaker and much more variable than expected, the mean Doppler shift was larger than expected, the Doppler broading was stronger than expected and also highly variable and there were significant anomalous events and their properties were also quite variable. All this findings attracted the interest of many solar physicists but "they were unable to explain even the gross features of the observations".
In early 1955, Burke and Franklin discovered strong radio bursts from the planet Jupiter. The picture on the right displays an example of Jupiter radiation recorded in 26.6 MHz at the Ohio State University, 1956 (Radio Astronomy, J. D. Kraus, ISBN 07-035392-1). The Jovian radio storms show maximum intensity between 10 and 40 MHz at a bandwidth of a few MHz drifting up or down in frequency with rates of 1 MHz per minute. On the other hand, the emissions are very weak between 40 and 400 MHz. The radiation is nonthermal, very intense and is procuded by energetic electron precipitation in Jupiter's auroral regions. To learn more about this fascinating subject, please visit the Radio JOVE project, the University of Hawaii Winward Community College Radio Observatory (including streaming audio) and the Society of Amateur Radio Astronomers (SARA), respectively.