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160 meters refers to the band of radio frequencies between 1,800 and 2,000 kHz, just above the mediumwave broadcast band. For many decades the lowest radio frequency band allocated for use by amateur radio, before the adoption, at the beginning of the 21st century in most countries, of the 630 and 2200 meter bands. Older amateur operators often refer to 160 meters as the Top Band[a] It is also sometimes referred to as the "Gentleman's Band" in contrast to the often-freewheeling activity in the 80 and 20 meter bands.
The 160 meter band is the oldest amateur band and was the staple of reliable communication in the earliest days of amateur radio, when almost all communications were over relatively short distances. The band was allocated on a worldwide basis by the International Radiotelegraph Conference in Washington, D.C., on 4 October 1927. The allocation at that time was 1715–2000 kHz. The International Radio Conference of Atlantic City reduced the allocation to 1800–2000 kHz under the provision that amateurs must not interfere with LORAN operation.
As the high frequency (HF) bands were developed in mid-1920s – along with their smaller, more feasible antennas – 160 meters fell into a period of relative nonuse. Although there has always been activity on the band, fewer and fewer hams are willing (or able, due to lack of sufficient real estate) to put up the antennas necessary to take advantage of the band's unique properties. For most amateurs, the HF bands are much easier to use, and HF antennas need a lot less real estate.
After World War II, the 160 meter band was apparently not coming back. A large part of the U.S. 160 meter band was allocated on a primary basis to the LORAN radio-navigation system that began operating in and around the 160 meter band in 1942. Amateurs were relegated to secondary, non-interfering status, with severe regional power limitations and restricted day/night operations on just a few narrow segments of the band.
Many older hams recall, with no great fondness, the ear-shattering buzz-saw racket of high power LORAN stations that began in 1942 until LORAN-A was phased out in North America on 31 December 1980, and most of the world by 1985. LORAN-A was still operating in China and Japan in 1995.
Great ingenuity was used to eliminate the pulse noise of the powerful LORAN-A transmitters through such famous circuitry as the "Select-O-Ject" of the late 1950s. The technology was adapted to modern noise blanking circuits used in current amateur receivers and transceivers.
Despite many obstacles and threats from commercial and military spectrum users, the efforts of a small number of determined 160 meter operators enabled the band to survive. In the UK it was the primary band for mobile operation for many years. The band experienced a rebirth with the demise of LORAN-A in the United States in December 1980, and the removal of power restrictions below 1900 kHz soon thereafter. Power restrictions above 1900 kHz were removed in March 1984, and 160 meters was then no longer regarded as the "orphan" band, as it had been for more than half a century.
Effective operation on 160 meters can be more challenging than most other amateur bands because of the sizes involved. Full-sized antennas (on the order of a quarter-wavelength or more) are over 130 feet for monopoles, which is also the recommended height for a horizontal dipole antenna, and square half-wave loops are nearly 70 feet high. If high power is used to compensate for an under-sized antenna, even the small antenna will require a similar-sized safety zone around it, free of people and animals. That much real estate may not be feasible for many amateurs, and even with space available, erecting and securing such a large antenna is a challenge. Nevertheless, many radio amateurs successfully communicate over very long distances with relatively small antennas. 160 meters is populated by many dedicated experimenters, as it is a proving ground for ingenuity in antenna design and operating technique.
During the day propagation is limited to local contacts, but long distance contacts are possible at night, especially around sunrise and sunset and during periods of sunspot minima. Much about ionospheric and propagation on 160 meters is still not completely understood. Phenomena such as "chordal hop" propagation are frequently observed, as well as other unexplained long-distance propagation mechanisms. Inexplicable radio blackouts – sometimes also encountered on the AM broadcast band – occur on 160 meters. Many of these phenomena have been investigated in the scientific community also.
The International Telecommunication Union allocated the frequencies from 1810–2000 kHz to amateur radio operations in ITU Region 1 (Europe, Greenland, Africa, the Middle East west of the Persian Gulf and including Iraq, the former Soviet Union and Mongolia) and 1800-2000 kHz in the rest of the world.
- "Top band" possibly refers to the position of 2000 kHz very nearly at the top of the medium frequency band (MF); it is the highest amateur band within MF.
- "International Radiotelegraph Conference" (PDF). Archived from the original (PDF) on 2014-03-08. Retrieved 2010-02-11.
- "International Radio Conference of Atlantic City (1947)" (PDF). Archived from the original (PDF) on 10 July 2012.
- "Amateur HF Bands". Retrieved 28 May 2013.
- "US Amateur Bands 2005" (PDF). Newington, CT: American Radio Relay League. Archived from the original (PDF) on 10 September 2005. Retrieved August 3, 2005.
- "2005 ARRL Band Plans". Newington, CT: American Radio Relay League. Archived from the original on 3 August 2005. Retrieved August 3, 2005.
- "Canada HF Band Plan" (PDF). RAC Web. Radio Association of Canada. Archived from the original (PDF) on 27 November 2010. Retrieved 8 July 2008.
- "Ham Radio QRP". Retrieved August 3, 2005.
- "UK Amateur Radio Band Plans". Retrieved February 3, 2010. (Click the [160 Meter] button at the bottom of the page.)
- "HF Amateur Bands". ITU Frequency Allocations. Retrieved January 1, 2008.
- "Bandplan" (PDF). IARU Region 1. Retrieved July 31, 2013.
- "Bandplan" (PDF). IARU Region 2. Retrieved January 1, 2008.
- "Bandplan" (PDF). IARU Region 3. Retrieved October 16, 2009.
- "Japan Bandplan" (PDF). Archived from the original (PDF) on 27 January 2011. Retrieved 30 March 2009.
- "NZ4O 160 meter propagation theory notes". Archived from the original on 23 September 2009. Retrieved 17 August 2009.
A website dedicated to layman level explanations of "seemingly" mysterious 160 meter (MF) propagation occurrences.