Shortwave listeners also collect QSL cards. Sometimes referred to as SWL cards, they can confirm reception of two-way amateur radio communications or commercial radio operators using HF frequencies. A more common form of QSL card for shortwave listeners to collect verifies the reception of signals from international broadcasting or utility stations.

For many international broadcasters, QSL cards serve as publicity tools rather than for gathering data on receptions. Often the cards include information about their stations or countries. Also, announcers may read on the air comments that listeners have put on their own QSL cards.

Other commercial and government television and radio stations have occasionally used QSL card requests as a means of judging the size of their audiences and distances that they can be received. Some of the very early television stations in New York City asked for listener reports, and HAARP program has occasionally requested reception information on its shortwave experiments, in return for which it sent back QSL cards. Time and frequency stations, such as WWV, will also send QSL cards in response to listeners reports. Other shortwave utility stations, such as marine and aircraft weather broadcasters, may QSL, as do some Pirate radio stations, usually through mail drop boxes.

From WIkipedia