In radiocommunication and radio broadcasting, QSL is one of the Q codes used in radiocommunication. A Q code message can stand for a statement or a question. In this case, QSL means either "do you confirm receipt of my transmission" or "I confirm receipt of your transmission". A QSL card is a written confirmation.
QSL cards are written confirmations of either a two-way radiocommunication between two amateur radio stations or a one-way reception of a signal from an AM radio, FM radio, or television station. They can also confirm the reception of a two-way radiocommunication by a third party. A typical QSL card is the same size and made from the same material as a typical postcard, and many are sent through the mail as a standard postcard.
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. The earliest reference seems to be a card sent in 1916 from 8VX in Buffalo, New York to 3TQ in Philadelphia, Pennsylvania (in those days ITU prefixes were not used). The standardized card with callsign, frequency, date, etc. may have been developed in 1919 by C.D. Hoffman, 8UX, in Akron, Ohio. In Europe, W.E.F. "Bill" Corsham, 2UV, first used a QSL when operating from Harlesden, England in 1922
Amateur radio operators exchange QSL cards to confirm two-way communications between stations. A QSL card sent from one amateur radio operator to another contains details about the contact and the station. At a minimum, this includes the call sign of both stations participating in the communications, the time and date of the contact (usually specified in UTC), the radio frequency used, the mode of transmission used, and a signal report. One national association of amateur radio operators, the ARRL, recommends a size of 3½ by 5½ inches (89 mm by 140 mm)
QSL cards are a ham radio operator's calling card and are frequently an expression of individual creativity—from a photo of the operator at his radio rig to original artwork, images of the operator's home town or surrounding countryside, etc. They are frequently taken with a good dose of individual pride. Consequently, the collecting of QSL cards of especially unique designs has become an add-on hobby to the simple gathering of printed documentation of a ham's communications over the course of his or her radio career. Some QSL cards contain an image, often something associated with the station or the operator.
QSL cards are sent either direct, using the ordinary postal system or via each country's centralized amateur radio association QSL bureau, which saves considerable postage fees by sending large numbers of cards to other bureaux using parcel services, although with a considerable delay. For rare countries, places with no reliable (or even existing) postal systems, and for expeditions to remote areas, a volunteer manager may handle the mailing of cards. (For expeditions this may amount to thousands of cards, and payment for at least postage is appreciated.)
Today, millions of cards annually move around the world. But even with batching by national societies and other organizations, postal costs are increasing. Thus, the use of electronic verification is growing and there are now at least two widely used systems for this. eQSL is the first and only global system to allow instantaneous electronic exchange of QSLs as jpeg images. The ARRL now has its Log Book of the World, LOTW, which allows confirmations to be submitted electronically for its DXCC award, but does not have actual QSLs for download.
QSL cards are often required when applying for an amateur radio operating award. Several alternatives to physical QSL cards that must be sent through the mail were developed in the 2000s. These systems use computer databases to store all the same information normally verified by QSL cards in an electronic format. Competing systems differ in their functionality and security requirements. Different sponsors of amateur radio operating awards may recognize only one such electronic QSL system in verifying award applications and many awards sponsors do not recognize any such electronic QSL system. Some awards programs use only electronic QSL information.
QSL cards are often fine historical or sentimental keepsakes of a memorable location heard or worked, or a pleasant contact with a new radio friend, and serious hams may have thousands of them. Some cards are plain, while others are multicolored and may be oversized or double paged.
An illustrated history of one amateur radio operator's life and QSL collection was published in 2003.
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 Project HAARP 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.