12-meter band
| 12-meter band | |
|---|---|
| Frequency range | 24.890–24.990 MHz, worldwide |
| Wavelength | About 12 m |
| Group | HF |
| US license | General and above, whole band |
| Operating | |
| Common modes | SSB (upper sideband), CW, FT8 and other digital modes |
| FT8 frequency | 24.915 MHz |
| Half-wave dipole length | About 19 feet (5.7 m) |
| Best time | Daytime, in the high years of the solar cycle |
The 12-meter band, 24.890 to 24.990 MHz, is a 100 kHz HF band between the 15-meter and 10-meter bands. Its fortunes rise and fall with the solar cycle, the roughly 11-year swing in the sun's activity. Near a solar maximum it is open to much of the world by day, and low power and small antennas go a long way; near a minimum it can be silent for long stretches, broken mainly by summer openings over shorter distances.
Twelve meters is the highest of the three WARC bands, with the 30-meter and 17-meter bands. All three were allocated to amateurs at the 1979 World Administrative Radio Conference (WARC-79) and opened to US amateurs during the 1980s, and by a convention written into band plans worldwide, none of them is used for contests. Like the other WARC bands, 12 meters has the same edges in every country.
Propagation
Long-distance signals on 12 meters depend on the F2 layer of the ionosphere, which must be strongly ionized to bend such high frequencies back to earth. That happens reliably only when the sun is active. In the high years of the cycle, the band typically opens in the morning, carries DX (long-distance contacts) through the day, and closes around or soon after sunset. Absorption is low at this frequency, so signals are often strong, and a 100-watt station with a simple antenna can work the world.
In the low years, F2 openings become rare and short, and the band may be closed to long distances for days or weeks at a time. Sporadic-E openings, caused by dense patches of ionization in the ionosphere's E layer, then provide most of the activity, chiefly in late spring and summer, with contacts of roughly 500 to 1,400 miles. Many operators watch the solar flux index, a daily measure of the sun's radio output; the higher the number, the better 12 meters tends to be.
What you'll find on the band
- 24.890–24.930 MHz is CW and digital. CW occupies the lower part; FT8 is at 24.915 MHz and FT4 at 24.919 MHz, with other digital modes nearby.
- 24.930 MHz carries a beacon of the NCDXF network, one of eighteen around the world that transmit in turn. Hearing them is a quick way to tell whether, and in which directions, the band is open.
- 24.930–24.990 MHz is voice, on upper sideband by convention.
Activity follows conditions closely. Near solar maximum the voice segment can be as lively as any band on HF, with DX stations and DXpeditions drawing crowds of callers. In quiet years the FT8 frequency may be the only sign of life for days.
US privileges
As on the other WARC bands, holders of a General, Advanced or Amateur Extra license may use all of 12 meters, and no segment is reserved for Extras. Technicians, who have voice privileges on part of the neighboring 10-meter band, have none on 12 meters.
Under the FCC's Part 97 rules, CW, RTTY and data are permitted from 24.890 to 24.930 MHz, and voice (phone) and image modes from 24.930 to 24.990 MHz. CW is allowed throughout the band, and the usual maximum of 1,500 watts PEP (peak envelope power) applies.
Antennas
Antennas for 12 meters are small. A half-wave dipole is about 19 feet long, and a quarter-wave vertical about 9½ feet tall. A two- or three-element Yagi is light enough for a small rotator, and hex beams and many multiband verticals include 12 meters along with the neighboring bands. Antennas this size are also practical for mobile and portable stations, and near solar maximum a mobile whip on 12 meters can make contacts across oceans.
Current HF transceivers cover 12 meters, but some radios built before the WARC bands opened do not.