Just above the mediumwave broadcast band, 160 meters is the lowest radio frequency band allotted for use by amateur radio operators in most countries. Seasoned operators refer to 160 meters as Top Band; it is also referred to sometimes as the "Gentlemen's Band" in comparison to the often-freewheeling 80 meters allocation. Effective 160 meter operation can be particularly challenging, as full sized antennas (on the order of a half-wavelength or more), are difficult to come by for many amateurs with limited space. Nevertheless, many radio amateurs successfully communicate over extremely long distances with relatively small antennas. 160 meters is populated by many hightly dedicated experimenters, as it is a proving ground for ingenuity in antenna design and operating technique. Much about ionospheric propagation on 160 meters is still unknown. Phenomena such as "chordal hop" propagation are frequently observed on "top band" as well as several unexplained long-distance openings. Additionally, inexplicable radio blackouts, such as are sometimes encountered on the A.M. Broadcast band, as well, can occur on 160 meters. Much speculation about these events has been put forth by the scientific community, and 160 meter operators are in a unique position to investigate such fascinating mysteries. The original "magic of radio" is very much alive and well on 160 meters.
160 meters has an interesting history in Amateur Radio, as well. It is one of the oldest amateur bands, and was the staple of reliable communication in the early days of Amateur Radio, when the majority of communications were relatively short distance. As the higher frequency bands were developed, along with the associated smaller, more convenient antennas, 160 meters fell in to a period of relative disuse. Although there has always been activity on the band, fewer and fewer hams were willing to put up the sort of antennas necessary to take advantage of the band's unique properties. The H.F. bands were so much easier to use, and used up a lot less real estate. Additionally, after World War II, a large part of the American 160 band was allocated to Loran navigational beacons. Regional power restrictions for the remaining sections of the band were put in place as well. Many older hams recall, with no great fondness, the ear-shattering racket of nearby Loran stations. Great ingenuity was used to eliminate the pulse noise of the powerful beacons, through such famous cicuitry as the "Select-O-Ject of the late 1950s," the technology of which was adapted to modern noise blanking circuits used in most current amateur receivers and transceivers. Despite the countless challenges thrust upon the small but dedicated band of 160 operators, the band survived. With the demise of Loran, the band experienced a new birth. The regional power restrictions have been removed, and 160 is no longer the "orphan" band it had been for nearly half a century.
That's what saying Wikipedia about the 160m band - interesting isn't it?
73, Petr OK1RP