Summer 2007 Issue

PROPAGATION

Calling All North American VHF Amateur Radio Operators!

By Tomas Hood, NW7US

What is the most exotic propagation mode you personally have experienced while operating on VHF? Pinging your signal off of a meteor trail? Catching aurora-mode DX? Making contacts by way of back-scatter propagation? Or have you worked stations in nearby states by way of sporadic-E propagation?

While there are a fair number of VHF operators manning the weak-signal and non-FM-mode segments of the VHF ham bands, there seems to be a significant lack of serious, systematic observations on a grand scale in North America. There are those involved with PropNET <http://propnet.org/>, and there are many who post individual spots on DX clusters. However, is there a concerted effort by the VHF community in North America to collect and study the vast operational data in a way that uncovers the rich VHF radio signal propagation phenomena that occur each season?

Such a systematic activity is alive and well in Europe. For instance, you can find a great amount of material presented at the “Amateur Radio Propagation Studies” website (http://www.df5ai.net/) by Volker Grassmann, DF5AI. He postulates, and I concur, that the absence of systematic studies of operational data is an obstacle in the discovery and deeper understanding of VHF radio propagation in North America. The majority of the studies Volker presents on his website are Eurocentric.

There are unanswered questions about VHF propagation in North America. For instance, Volker points to the different propagation characteristics of Europe and North America during the sporadic-E season between May and September. Does sporadic-E activity in North America track with the level of activity in Europe, or are there vastly different systems at work in the sporadic-E season in each area of the world?

Because there does not seem to exist any systematic collection of daily and seasonal VHF DX information on a grand scale (more than a handful of die-hard VHF stations posting on DX reflectors), it is difficult to analyze the real VHF propagation phenomena across the vast geographical area of North America. Scientific background data such as ionosonde, sferics, and upper-air sounding data is easily obtained. However, there’s very little information from the VHF community about daily continent-wide propagation on a grand scale (hundreds of operators representing all of the geographical regions).

What is FAI?

An example of what needs to be studied by the VHF community is the Field-Aligned Irregularities (FAI) related propagation modes. A field-aligned irregularity is a dense “cloud,” or bubble, that becomes aligned with the powerful geomagnetic field lines that run from each of the Earth’s poles.

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