80 Metres, 3.5 – 3.8MHz
During the day, absorption in the D-layer of the ionosphere limits contacts to a few hundred miles, but at night and especially in winter when noise levels are lower, it offers worldwide DX possibilities.
In the UK, and most of Region 1, the band is shared with other services which may be heard occasionally using upper sideband (USB). Outside Region 1, the 80 metre allocation extends up to 4MHz, so amateur signals, especially from the US, may be heard at night above 3.8MHz and will often work split if looking for Region 1 contacts. In the US, these frequencies from 3.8 – 4.0MHz are referred to as the 75 metre band.
The CW segment from 3560 – 3580kHz and the SSB segment from 3650 – 3700kHz are designated as contest-free sections of the band in Region 1 and should be kept free of contest activity during Region 1 contests, although during major international events, it is likely that the whole band will be occupied. Likely! hi hi no it is a certainty!
There are designated DX windows from 3500 – 3510kHz (CW) and 3775 – 3800kHz (SSB) which should be kept clear for intercontinental traffic and not used for local QSOs.