JT65HF

JT65HF is a digital mode designed for weak signal communication on the High Frequency (HF) bands. It was developed by Joe Taylor, K1JT, building on his earlier work with the JT65 mode, which was originally intended for Moonbounce (EME) communication. The "HF" designation indicates its suitability for terrestrial HF operations.

The JT65HF mode is characterized by its highly efficient encoding and decoding algorithms, allowing reliable communication even with extremely weak signals, often below the audible threshold of the human ear. This is achieved by transmitting a very slow stream of data, with each transmission lasting approximately 2 minutes. The digital signal is then processed to extract the transmitted message, even in the presence of significant noise and interference.

JT65HF is primarily used by amateur radio operators for making contacts over long distances, often referred to as DXing. Its ability to work with weak signals makes it effective when propagation conditions on HF are poor. The mode typically uses specific bandwidths within the amateur radio bands, and specialized software is required to generate and decode the signals. Common operating frequencies are found within the popular HF bands like 20 meters, 40 meters, and 80 meters. While originally developed for specific purposes, its utility has made it a popular choice for many radio amateurs seeking to extend their communication reach.