Radio Propagation Analysis Software
Analyses, studies, simulations, predictions
Special topics (1)
On July 22, 2002 the BeamFinder version 1.0.0 was introducted in the community of radio amateurs. At that time, the BeamFinder software was an extra feature of the Amateur Radio Propagation Studies web site, i.e. www.df5ai.net (click the arrow-button in the above navigation panel to access df5ai.net). In fact, the software has contributed to many analyses in VHF radio propagation and it is perhaps worth to mention some of the results BeamFinder made available to radio amateurs.
Geographical signature of Auroral and FAI backscatter
Aurora and FAI dx communication is associated with backscatter of radiowaves aligned to the Earth magnetic field. BeamFinder may calculate direction and magnitude of the Earth magnetic field for any place in the world, i.e. on ground and in the atmosphere as well. Thus, the software may analyse potential locations of backscatter and may display potential positions of dx targets you may access in dx openings. Similiar software solutions exist on scientific mainframe computers for many decades, but it wasn't generally available to radio amateurs and it wasn't optimized for VHF dx communication purposes. Plots similiar to the graphics on the right, is -as far as I can see (please correct me if I am wrong)- something new in ham radio. You may now evaluate your personal dx range in Auroral and FAI communication and you may identify geographical regions enabling backscatter dx QSOs.
Revealing the nature of the so-called 'unusual Aurora QSOs'
For many years, radio amateurs are baffled because of unusual Aurora QSOs which shouldn't exist at all. The dx distance is typically much longer compared to 'ordinary' Aurora dxing and the backscatter originates from geographical regions which were believed ineffective in Auroral backscatter. There are many examples of unusual Aurora QSOs, it is a rare phenomenon though and we couldn't explain the 'geometrical rules' behind it, i.e. the backscatter geometry. Designing BeamFinder's user interface, I considered user access to a couple of model parameters in the software's preferences section, hoping it might be useful some day in order to optimize BeamFinder's accuracy even more. One of this parameters is the so-called aspect angle which controls the direction of backscatter. This angle is 90 degree in Auroral backscatter but I learned from ionospheric radar systems that field-aligned backscatter may sometimes show aspect angles deviating from perpendicularity by a few degree. To be honest, I never expected we would find something similiar in amateur radio.
This parameter was actually the key for interpreting examples of unusual Aurora QSOs by using BeamFinder. Manipulating the aspect angle (in one example, by considering a noteworthy offset of 20 degree), BeamFinder was capable to explain this unusual QSOs more or less perfectly. Meanwhile, I have analysed many unusual Aurora QSOs and in all cases, BeamFinder was able to explain the backscatter geometry with high degree of accuracy. Thus, BeamFinder discovered a feature which was never communicated before in amateur radio propagation.
Double hop sporadic E in 144 MHz
In 2003, European ham operators were more than surprised about a series of spectacular sporadic E openings in 144 MHz. On May 20, 2003 radio amateurs from the Canary Islands reported many 144 MHz QSOs to central Europe corresponding to radio path lengths of 3.000 to more than 3.500 kilometers. I had the pleasure to discuss this remarkable opening with Udo, DK5YA, and we finally decided to analyse this event in more detail. Using BeamFinder's multiple hop analysis routines, we soon realized that this example of double hop sporadic E is a special one because the midpoints of the zigzag propagation path between ground and the ionosphere are all located on the Iberian Peninsula. Thus, there is strong indication of ground reflection of radiowaves by land and, most surprising, the path centers appear to correlate to the position of inland lakes and major rivers.
The assumption of surface reflection by inland water expanses (in the paper, we called it radioglint in inland lakes) is however not yet verified. It is perhaps nothing else than a funny idea, maybe it is an existing but unusual phenomenon in ham radio propagation. In a second analysis, this concept was extrapolated to other regions in Europe, e.g. to the lake Balaton in Hungary. Assuming this lake would represent a reflecting surface in the center of the propagation path, enabling double hop propagation by mirroring the first skip back into the ionosphere, we may predict a couple of dx opportunities in double hop sporadic E. Using BeamFinder, this analysis was an easy thing to do leading to surprising results: 'historical' examples of double hop sporadic E appear to correspond to BeamFinder's findings quite accurately. Hence, there is perhaps an element of truth in this radioglint hypothesis.