| 10 meters is one of the many amateur radio bands available to hams worldwide. In the US, the allocation ranges from 28.0 to 29.7 MHz, leading to wavelengths of 10.7 and 10.1 meters at the two band edges.
This band is one of the most popular ham radio bands out of all the ones in the HF spectrum. It's unique in that it's unusually large in terms of relative bandwidth (1.7 MHz), compared to other HF bands where the maximum allocations are around 400 kHz of space.
It's also called the magic band, and with good reason. When the sunspot numbers are high, and there exists enough ionization in the F layers of the ionosphere, signals transmitted on 10 meters will bounce around the earth for a really long time. Far enough in fact that when conditions are right, you can talk to people on the opposite sides of the earth (15k-20k miles).
At the 10 meter wavelength, directional antenna designs such as quads and yagis with large numbers of directive elements (8-10) become practical, allowing you to get a antenna with some BIG gain (10-15 db over ground compared to a dipole antenna) in the transmitting system. The only downside of antenna building for 10 meters is that it is quite difficult to build an antenna that has large gain and good SWR over the entire 1.7 MHz of the band. Often, compromises have to be made, i.e. designing the antenna for a slice of the band and sticking to that piece only.
When the band is really "open", signals are easily bouncing off the ionosphere allowing you to make long distance contacts, and elaborate antennas aren't necessary to talk a long way. Simple dipole and vertical antennas will do the job. Portable and handheld radios will also work, and work well. Amazingly, when 10 meters is hot, the power output really doesn't matter all that much. You can be in Kansas and talk to Australia with a vertical antenna and 5 watts just as well as a guy with a $1,200 yagi antenna and 1,000 watts of power. I've done it. Hence, the "magic" band.
Since 10 meters is very dependent on the ionizing radiation of the sun, once the F layers have given up their ions at night, the band is generally useless except for local communication. There exists however a phenomenon called sporadic E, where 10 meter signals will bounce off random patches of ionization in the E layer of the ionosphere at night time. This allows point to point communication over distances up to 2,000 miles. Generally these phenomena are most prevalent in the late spring and early summer (in the US), but have been known to occur at other times of the year too. Predicting a sporadic-E opening is not an easy task - the band may be dead six nights in a row, and then signals pour in on the seventh. The best way to look for openings is to turn on your radio and listen. You may hear a couple of local guys talking 1,000 miles away who think no one can hear them .. break in and suprise them!
How and where will 10 meters be open? From the eastern US, openings to Europe and Africa generally occur in the first few hours after the sun rises in the morning, where it illuminates the ionosphere for the eastern path. Communication on the band throughought North and South America is usually possible throughout the day. Openings to Oceania and Asia usually occur late in the afternoon as the sun is setting, in much the same way as openings to the east earlier in the day. Conditions from other locations will of course vary.
When sunspot numbers are low, 10 meters can be a very lame experience. This amounts to turning on the radio for a week at a time and hearing nothing at all. Unfortunately, this occurs often during lows in the solar cycle. If you find yourself in this situation, go down to 17 meters and bide your time until the next peak!
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