Foundations of Amateur Radio

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Sun-Spots and Amateur Radio

Posted: 11 Feb 2017 09:00 AM PST


Foundations of Amateur Radio Amateur Radio as a hobby is one of those
activities that covers a wide range of pursuits. A fellow Amateur once
referred to it at 1000 hobbies in one. I like that as a description, but it
really doesn't cover how wide and extensive this hobby really is. You've
heard me talk about radios and on-air activity, about contesting, about out
door activities, about electronics and antennas, about the grey line and
about decibels. Today I'm going to talk about the Sun. Using a hand-held
radio you're often using higher frequencies, 2m, or 144 MHz or higher.
These radio waves mostly travel along line-of-sight. If you look at the
lower frequencies, called HF, 28 MHz, 21 MHz, or lower, then those radio
waves also travel line-of-sight, but they also travel up into the
ionosphere surrounding the earth. If you manage to hit the angle just
right, then some of those will reflect off the ionosphere back to earth.
It's a lot like skipping a stone on a pond. If you get it right, you might
make it skip several bounces, if you get it wrong, it will go "plop" and
vanish. The same is true for these frequencies. One of the things that
makes the ionosphere reflective to radio waves of a certain frequency is
the level of ionisation in this area around the globe. Typically the
ionosphere is somewhere between 50km and 1000km above you right now. At
different heights the ionosphere reacts differently and the Sun shining on
it will alter the properties as the day unfolds. This is why when night
turns into day and day turns into night, special things start happening
along the border between day and night, the so-called grey line where it's
not quite day and it's not quite night. One way of looking at this is that
the ionosphere heats up during the day. Now heat is an interesting thing.
The Sun shining on your skin is experienced as heat, but what's actually
happening is that the radiation from the Sun is exciting the electrons on
your skin and you experience that as heat. As a matter of interest, the Sun
generates about 650 Watts per square meter in the middle of the day coming
through the atmosphere. That's about 650 Joules of Energy per second per
square meter. Lots of excitement. At the outside of the earth, there's
about 1300 Watts per square meter. The difference, 650 Watts, is absorbed
by the atmosphere. So, the equivalent of the heat you feel on your skin is
also heating up the atmosphere. Now, this "heat" is really energy that's
exciting electrons and thus also exciting the ionosphere. At the simplest
level this is making the ionosphere more reflective to radio waves. I'm
deliberately simplifying this because I don't want to get bogged down into
how precisely, because my point is about the Sun and more specifically
about Sun-spots. There I said it, Sun-spots. What are they and what do
they have to do with anything? Well, a Sun-spot is a cool place on the
Sun. When I say cool, it's about half as warm at a Sun-spot than the area
around it, only 3000 degrees Celsius, instead of 6000 degrees. Sun-spots
appear in pairs on opposite sides of the Sun and represent a point on the
Sun where an intense magnetic field comes through the Sun. You can think of
it as a huge race-track through the Sun that accelerates particles from the
Sun into space. These particles represent energy and if they happen to hit
the earth, they add a whole lot of extra energy to the ionosphere, making
it much more reflective. The more Sun-spots, the more energy, the more
excitement of the ionosphere, the more reflection, the better radio
communications. Sun-spots generally appear in groups and the density of
these groups varies over time. To get a uniform sense of how much energy
there is around, scientists came up with a Sun-spot number. It's indicative
of how much activity there is, not an actual count of the number of dots on
the Sun, since some spots are large and others are relatively small. The
increase and decrease of solar activity...
This posting includes a media file:
http://podcasts.itmaze.com.au/founda...teur-radio.mp3