160 metres

160 metres, often known as Top Band, is technically a Medium Frequency (MF) band, the only one licensed to amateurs. It is slightly higher in frequency than the AM broadcast band (540 kHz - 1600 kHz), and behaves similarly. 160 meters is the lowest-frequency band on which amateurs are licensed to operate.

Equipment
Most amateur HF equipment supports the 160 metre band. However, it can be challenging to put up a full-size antenna on this band. Many operators use an inverted-L antenna for 160.

Modulation
Operation on the 160 metre band is primarily CW and SSB, but operators also use modes appropriate for HF such as RTTY and SSTV.

Propagation
Radio communication on 160 metres is prone to extreme D-layer absorption during the day. This typically limits communication to 75 miles. At night, however, the D-layer weakens and contacts can be mode over thousands of kilometres. Like the HF bands, 160 metres usually supports such long-distance communication through refraction of signals via the F2 layer.