Amateur Radio Propagation Studies
Science, research, engineering, operating
Intense tropospheric inversion layers may result in the ducting of radiowaves which enables long distance radio propagation in VHF, UHF and SHF too. In this section, we will analyse this type of long distance propagation in detail. We will also speculate about another propagation mode that has not been observed yet but many radio amateurs are conviced it will be observed, sooner or later, i.e. terrestrial transatlantic radiowave propagation in the 144 MHz band. In fact, radio amateurs are still awaiting their Christopher Columbus and their Charles Lindbergh, i.e. the very first ham pioneers crossing the Atlantic Ocean in VHF dx communication. The -icon indicates articles referring to the BeamFinder analysis software.
In August 2005, VHF radio amateurs have reported record-breaking results in tropospheric dxing. The article discusses the dx QSOs established by G4LOH, EI5FK and RW1ZC/mm on August 7, 15 and 29, respectively. To explain the meteorological origin of this extraordinary dx QSOs between western Europe and west Africa, upper air sounding data (see the links in the METEO realtime section of this web site) has been analysed and the vertical distribution of the atmospheric refractive index has been calculated along the 3700km radio propagation path. Between the northwest of Spain and the Canary Islands, intense inversion layers are found between 1000m and 2000m altitude indicating significant discontinuities in air temperature and, in particular, in air humidity. Thus, significant discontinuities are also present in the vertical distribution of the atmospheric refractive index which has apparently enabled ducting of radiowaves and, in consequence, long distance 144 MHz communication links.
Tropospheric dx QSOs exceeding the distance of 3.000 kilometers must be considered a true rarity in amateur radio. By referring to various ham radio resources, a list of almost 100 examples of very long distance tropo QSOs is obtained which reveals a number of systematical features. All these QSOs accumulate in only four geographical areas located around 20° and 30° latitude north and south of the Earth's equator and represent radiowave propagation across large water expanses excluding continental radio paths. The frequency of occurrence appears to indicate a periodical behaviour between years of high and low dx activity. It is shown that all very long distance tropo QSOs are closely related to each other and result from the specific meteorological conditions at the horse latitudes which are caused by the Hadley convection cells on both sides of the equator. The paper discusses the possible correlation between the occurrence of very long distance band openings and seasurface temperature variations in the oceans. The results are extrapolated to other regions in the world which indicate a number of future dx opportunities in ham radio.
Being a radio amateur, Andrew (VK3KAQ) is familar with tropospheric dxing in Western Australia and Victoria on the bands from 50 MHz to 1296 MHz and he designs and optimzes fixed microwave links in the commercial frequency bands below 10 GHz. In a detailed paper, Andrew summarizes the obervational characteristics of tropospheric ducting of radiowaves, explains the findings of the SODAR measurements (which represents an acoustic radar system investigating the lower atmospheric between ground and a height of 1000 to 2000 meters), provides an introduction to the theory and, finally, assembles a consistent picture about the myths and facts in tropospheric duct propagation.
Terrestrial QSOs in 144 MHz exceeding the dx distance of 3.000 kilometers and even more, is indeed a rare phenomenon but cannot be considered sensational because of the many very long distance QSOs in the history of VHF amateur radio. From this perspective, terrestrial transatlantic VHF communication between, for example, Ireland and Newfoundland is comparable to 144 MHz dx QSOs between Germany and the Canary Islands. In both cases, the geographical distance is 3.000 to 3.200 kilometers. However, the 'emotional distance' differs by lightyears. Radio amateurs still await their Christopher Columbus and their Charles Lindbergh, i.e. the very first ham pioneers crossing the Atlantic Ocean in terrestrial VHF dx communication. For this reason, radio amateurs deployed a number of so-called transatlantic beacons on both sides of the Atlantic Ocean, hoping its signals will sooner or later appear on the opposite side of the big pond - without any success so far. Does geophysical reasons exclude terrestrial transatlantic VHF communication? Or does the absence of transatlantic QSOs result from statistics because of too little observational efforts? Many radio amateurs consider transatlantic VHF propagation an opportunity reserved to coastal radio stations. Not quite right when considering double hop sporadic E a potential propagation mode in transatlantic VHF communication.
Radio amateurs are familiar with transatlantic QSOs in 50 MHz. Our colleagues in BC/TV dxing report reception of 90 MHz FM broadcast from Canada and the U.S. in Northern Ireland and Scotland. American 100 MHz service stations were heard by airplanes and navy vessels travelling close to the Irish westcoast (see the below article and the references therein) - but 144 MHz radio amateurs are still waiting in the queue. However, claimed reception of North-American 144 MHz transatlantic beacons in Europe exist for long time. In December 2002, this web site received Sebastian's (DH3YAV) report claiming reception of the Canadian 144 MHz beacon VE1SMU in Germany. Read the Sherlock Holmes type of investigation analysing his observation, the results we found and the readers' comments.
[April, 2004]. Do you understand why men are climbing on the highest mountains and are sailing around the world in a nutshell? They could do much easier by using heliocopters and jet planes in order to visit hill tops and distant countries. If you do then you also understand the reason why a couple of radio amateurs wish to establish terrestrial radio links across the Atlantic Oceans on very high frequencies instead of using one of the many amateur radio satellites orbiting around Earth. Yes, crossing the big pond on VHF is indeed a major challenge and the Irish Radio Transmitters Society will award those radio operators who first establish two-way communication in 144 MHz between the continents of Europe and America, see the two crystal trophies on the right. Well, this lovely trophies are still sitting in Dublin awaiting to be celebrated some day in the future.