QSL card

Collecting these cards became popular with radio listeners in the 1920s and 1930s, and reception reports were often used by early broadcasters to gauge the effectiveness of their transmissions.

[2] The concept of sending a post card to verify reception of a station (and later two-way contact between them) may have been independently invented several times.

At a minimum, this includes the call sign of both stations participating in the contact, the time and date when it occurred (usually specified in UTC), the radio frequency or band used, the mode of transmission used, and a signal report.

[4] The International Amateur Radio Union and its member societies recommend a maximum size of 3+1⁄2 by 5+1⁄2 inches (90 by 140 mm).

Consequently, the collecting of QSL cards with especially interesting designs has become a frequent addition to the simple gathering of printed documentation of a ham's communications over the course of their radio career.

[7] For rare countries, that is, ones where there are very few amateur radio operators, places with no reliable (or even existing) postal systems, including expeditions to remote areas, a volunteer QSL manager may handle the mailing of cards.

For expeditions this may amount to thousands of cards, and payment for at least postage is appreciated, and is required for a direct reply (as opposed to a return via a bureau).

[10] The High Frequency Active Auroral Research Program has occasionally requested reception information on its shortwave experiments, in return for which it sent back QSL cards.

[11] Standard frequency and time stations, such as WWV, will also send QSL cards in response to listeners reports.

[14] A simple card format might only include the user's callsign and/or "handle", home location, and note the date and time of a CB radio contact.