Thursday, May 10, 2012

The business of forecasting is a tricky one. Take weather forecasting for example. As we know, in spite of all the modern day technology available to meteorologists, there are still times when they manage to make mistakes. It’s happened to all of us at some stage, leaving the house without an umbrella because the forecast said it was going to be sunny, and getting soaked in a rain shower.

It seems like radio propagation forecasting is similar. For many years, propagation scientists have used data such as sunspot numbers, the 10.7cm solar flux data, and x-ray info, to predict how good or bad radio propagation will be on different frequencies, at different times, and to different areas of the world. Nowadays, with the advent of things like SoHo (Solar and Heliospheric observatory, run by NASA), things should be even easier. Today, I checked out the solar conditions on and saw a solar flux of 128, which should give reasonable conditions on the HF bands, but, a high A index of 24, and an X-ray count of B6.6, indicating high absorption in the D layer of the earth’s ionosphere. This absorption prevents signals reaching the higher E and F layers where they would normally rebound back down to earth.

Yesterday, with the A index around 10, conditions were already starting to decline a bit, and it would have seemed normal that today, there would be a “best band” somewhere between 17 and 10 meters, just below the MUF (maximum useable frequency). The rig was left on 20m from yesterday, so I put the 20m antenna on without much hope of anything. It was on 14180 so I tuned up the band, past 195 so as not to upset any possible DXpeditions, and parked on 14205. I heard just one lone Italian station, on a segment which is normally chock a block with stations. I called, without much hope of getting an answer, and when I unkeyed the mike, was surprised to hear a small pileup of strong stations. VK5LB, on his farm near Adelaide, Australia, was first in the log, putting out an impressive signal with his homemade rig and amplifier into a small wire antenna. He was followed by a steady stream of stations from Australia, New Zealand, USA, and the odd European, all with strong signals, until it was time to pull the plug.

So it just goes to show. Although the forecast nowadays is usually right, it’s a good idea to have an umbrella in the car just in case….or, to try a band that shouldn’t in theory be open!

No comments: