How to Get Started:
Beyond FM: Solar Influences at VHF
By Jim Aguirre, W7DHC
This month, I was going to take a look at antennas for the VHF/UHF and microwaves; however, since we recently had a natural event which had a major impact on communication on some of those bands, I decided to talk about it. We'll explore antennas next month.
The 'natural event' I referred to is a series of sunspot eruptions'frequently called 'solar flares' that began on March 28 and continued through April 4. Solar flares can occur at any time, but are much more frequent at the peak of a solar cycle. We have just passed the solar maximum of Cycle 23 and can expect increased solar flare activity.
When a solar flare occurs, it sends out a blast of energy in the radio and magnetic spectrum that can have significant impacts on communication and electrical generation facilities. There are three classes of solar flares, X, M and C. C-class flares are small and little, if any, impact on the earth can be anticipated. M-class flares are much larger and noticeable impacts can be expected. X-class solar flares are the 'Big Daddies' of the universe, sending out huge amounts of solar radiation that can cause severe disruption. A large X-class flare in 1989 damaged electrical generation equipment in Canada. Each class has a range of severity graded by an associated number; X-8 flare would be more severe than an X-5.
Why all this interest in solar flares if they 'disrupt' communication? Well, remember that I said 'broadcast and HF amateur bands' are affected. Left unsaid was the fact that the larger solar flares set off the Aurora Borealis "Northern Lights" and that provides some wild propagation on the lower VHF/UHF bands. Aurora is a highly charged electrical display in the visible light spectrum, creating a reflecting medium for radio signals on six meters through 70 centimeters - possibly even higher.
Did you notice a pink-purple-orange glow to the North on Friday night, March 30th? We had a huge Aurora going on. Unfortunately, the sky was cloudy, so only a glow was noticeable and only in areas where there wasn't much man-made light.
On March 28, two M-class flares erupted in close succession. They were followed by a large X-14 flare on March 29th. While this third flare was big enough to have a huge impact on its own, when it reinforced the earlier flares, we experienced Aurora that was visible as far south as Mexico. That's big-time Aurora!
As a result, the six-meter band went wild. Pointing antennas to the North'into the major portion of the Aurora'resulted in six-meter contacts being made throughout a wide area of the West and beyond. I worked 20 different grids in the four hours or so I was on, from Utah to California. The following morning, the Aurora was still there and some Puget Sound area operators worked similar contacts on two meters (144 MHz) and one-and-a-quarter meters (222 MHz), as well as on six meters. I missed that one due to other commitments; darn!
Not content with her handiwork, Mother Nature finished off the activity with a record-setting X-20 flare - the largest ever recorded. Fortunately, the earth's position with respect to the sun had change by the time it occurred and the majority of the big blast went out into space. Had it been directed toward the earth as the earlier flares were, it is likely that substantial damage would have been done to communications and electrical generation facilities.
On the other hand, it likely would have created 'The Mother of All Auroras' and the resulting VHF/UHF activity would have been incredible. I almost wish; well, maybe not, considering the amount of damage that might have been done.