Summer 2006 Issue

PROPAGATION

The New World of VHFing

By Tomas Hood, NW7US/AAAŘWA

High-frequency radio enthusiasts can hook up a light bulb and communicate with the world, when propagation conditions are “just right.” Better yet, just string up some wire, tune it up to a transceiver, and talk around the world.

At least, that’s how things work from the perspective of DXers enjoying the worldwide around-the-clock excitement of HF signals propagating when the Sun is popping with flares and peppered with sunspots during the peak years of a solar cycle. However, this cycle is just about at its end, and quiet solar conditions have all but put a wet towel on worldwide around-the-clock HF propagation.

While HF radio DXers long for the coming upswing of the next solar cycle, Cycle 24, rumor has it that the folk on VHF and higher frequencies are out in full force, working “real radio.” They cook their meals in front of their portable parabolic dish antenna, while trying to set new distance records. They bounce signals off the moon or off plasmatic meteor trails. Their DX is a raspy-sounding Morse code signal propagated by way of backscatter, aurora, and sporadic-E. A VHFer has to have more than a wet noodle or the losses will make the antenna system nothing more than a dummy load (at best, although read about a VHFer who could work a local repeater using a wet T-shirt).

Propagation on VHF and above is not quite the same as it is on HF. Sure, F-layer refraction takes place at times on 6 meters and a bit higher, and it is true that sporadic-E works on HF, but there is a whole different and exciting set of modes and techniques unique to VHF and up.
Is it possible to predict propagation conditions and DX openings on the frequencies above 30 MHz? Are there reliable models that enable us to forecast sporadic-E, aurora, tropospheric ducting, and other known (or unknown) propagation modes?

After many decades of on-air experience, the amateur and scientific communities are still struggling to find a practical understanding of the complex modes of propagation unique to VHF and above.
 

The live display of 6-meter operators as spotted and mapped at the <http://chat.dxers.info/> site that Tim Havens, NN4DX, provides to the VHF community.

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