High frequency (HF) is the range of radio frequency electromagnetic waves “radio waves” between 3 and 30 MHz. It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters [ten to one hundred metres]. Frequencies immediately below HF are denoted medium frequency [MF], while the next band of higher frequencies is known as the very high frequency [VHF] band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere, a method known as “skip” or “skywave” propagation, these frequencies are suitable for long-distance communication across intercontinental distances. The band is used by international shortwave broadcasting stations (2.31–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.
The dominant means of long distance communication in this band is skywave “skip” propagation, in which radio waves directed at an angle into the sky reflect, actually refract, back to Earth from layers of ionized atoms in the ionosphere. By this method HF radio waves can travel beyond the horizon, around the curve of the Earth, and can be received at intercontinental distances. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:
- Sunlight/darkness at site of transmission and reception
- Transmitter/receiver proximity to solar terminator
- Sunspot cycle
- Solar activity
- Polar aurora
Amateur Radio HF Bands
- 80 meters – 3.5-4 MHz (3500–4000 kHz) – Best at night, with significant daytime signal absorption. Works best in winter due to atmospheric noise in summer. Only countries in the Americas and few others have access to all of this band, in other parts of the world amateurs are limited to the bottom 300 kHz or less. In the US and Canada the upper end of the sub-band from 3600–4000 kHz, permits use of single-sideband voice as well as amplitude modulation, voice; often referred to as 75 meters.
- 60 meters – 5 MHz region – A relatively new allocation and originally only available in a small number of countries such as the United States, United Kingdom, Ireland, Norway, Denmark, and Iceland, but now continuing to expand. In most ( but not all ) countries, the allocation is channelized and may require special application. Voice operation is generally in upper sideband mode and in the USA it is mandatory.
- 40 meters – 7.0–7.3 MHz – Considered the most reliable all-season DX band. Popular for DX at night, 40 meters is also reliable for medium distance (1500KM) contacts during the day. Much of this band was shared with broadcasters, and in most countries the bottom 100 kHz or 200 kHz are available to amateurs. However, due to the high cost of running high power commercial broadcasting facilities; decreased listener-ship and increasing competition from net based international broadcast services, many ‘short wave’ services are being shut down leaving the 40 meter band free of other users for amateur radio use.
- 30 meters – 10.1–10.15 MHz – a very narrow band, which is shared with non-amateur services. It is recommended that only Morse Code and data transmissions be used here, and in some countries amateur voice transmission is actually prohibited. For example, in the US, data, RTTY and CW are the only modes allowed at a maximum 200w peak envelope power (PEP) output. Not released for amateur use in a small number of countries. Due to its location in the centre of the shortwave spectrum, this band provides significant opportunities for long-distance communication at all points of the solar cycle. 30 meters is a WARC band. “WARC” bands are so called due to the special World Administrative Radio Conference allocation of these newer bands to amateur radio use. Amateur radio contests are not run on the WARC bands.
- 20 meters – 14.0–14.35 MHz – Considered the most popular DX band; usually most popular during daytime. QRPoperators recognize 14.060 MHz as their primary calling frequency in that band. Users of the PSK31 data mode tend to congregate around 14.071 MHz. Analog SSTV activity is centered around 14.230 MHz.
- 17 meters – 18.068–18.168 MHz – Similar to 20m, but more sensitive to solar propagation minima and maxima. 17 meters is a WARC band.
- 15 meters – 21–21.45 MHz – Most useful during solar maximum, and generally a daytime band. Daytime sporadic-E propagation (1500 km) occasionally occurs on this band.
- 12 meters – 24.89–24.99 MHz – Mostly useful during daytime, but opens up for DX activity at night during solar maximum. 12 meters is one of the new WARC bands.
- 10 meters – 28–29.7 MHz – Best long distance (e.g., across oceans) activity is during solar maximum; during periods of moderate solar activity the best activity is found at low latitudes. The band offers useful short to medium range groundwave propagation, day or night. During the late spring and most of the summer, regardless of sunspot numbers, afternoon short band openings into small geographic areas of up to 1500 km occur due to Sporadic-E propagation. “Sporadic-E” is caused by areas of intense ionization in the E layer of the ionosphere. The causes of Sporadic-E are not fully understood, but these “clouds” of ionization can provide short term propagation from 17 meters all the way up to occasional 2 meter openings. FM operations are normally found at the high end of the band (Also repeaters are in the 29.5 – 29.7 MHz segment in a lot of countries).
- 160 meters – 1.8-2 MHz (1800–2000 kHz) – Often taken up as a technical challenge; as long distance (DX) propagation tends to be more difficult due to higher D-layer ionospheric absorption. Long distance propagation tends to occur only at night, and the band can be notoriously noisy particularly in the summer months. 160 meters is also known as the “top band”. Allocations in this band vary widely from country to country. This band lies just above the commercial AM broadcast band.
Contesting is one of the great activities of Amateur Radio. It boosts your technical knowledge and improves your radio operating skills helping make you a better Amateur.