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A QSL card is a written confirmation 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, television or shortwave broadcasting station. It can also confirm the reception of a two-way radiocommunication by a third party listener. A typical QSL card is the same size and made from the same material as a typical postcard, and most are sent through the mail as such.
QSL card derived its name from the Q code "QSL". A Q code message can stand for a statement or a question (when the code is followed by a question mark). In this case, QSL? means "do you confirm receipt of my transmission?" while QSL means "I confirm receipt of your transmission".
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.
Usage in amateur radio 
Amateur radio operators exchange QSL cards to confirm two-way radio contact between stations. Each card contains details about one or more contacts, the station and its operator. 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. The International Amateur Radio Union and its member societies recommend a maximum size of 3½ by 5½ inches (140 mm by 90 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 station to original artwork, images of the operator's home town or surrounding countryside, etc. They are frequently created with a good dose of individual pride. Consequently, the collecting of QSL cards of especially interesting 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.
Normally sent using ordinary, international postal systems, QSL cards can be sent either direct to an individual’s address, or via a country's centralized amateur radio association QSL bureau, which collects and distributes cards for that country. This saves postage fees for the sender by sending several cards destined for a single country in one envelope, or large numbers of cards using parcel services. The price for lower postage, however, is a delay in reaching its destination because of the extra handling time involved.  In addition to such incoming bureaus, there are also outgoing bureaus in some countries. These bureaus offer a further postage savings by accepting cards destined for many different countries and repackaging them together into bundles that are sent to specific incoming bureaus in other countries. Most QSL bureaus operated by national amateur radio societies are both incoming and outgoing, with the notable exception of the United States of America, and are coordinated by the International Amateur Radio Union (IARU).
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).
Recently, the Internet has enabled electronic transmission as an alternative to the need for mailing a physical card. These systems use computer databases to store all the same information normally verified by QSL cards in an electronic format. Some sponsors of amateur radio operating awards, which normally accept QSL cards for proof of contacts, may also recognize a specific electronic QSL system in verifying award applications.
- One such system, called eQSL, enables electronic exchange of QSLs as jpeg or gif images which can then be printed as cards on the recipient's local inkjet or laser printer, or displayed on the computer monitor. Many logging programs now have direct electronic interfaces to transmit QSO details in real-time into the eQSL.cc database. CQ Amateur Radio magazine began accepting electronic QSLs from eQSL.cc for its four award programs in January 2009. 10-10 has been accepting eQSLs since 2002.
- Another system, the ARRL’s Logbook of The World (LoTW), allows confirmations to be submitted electronically for that organization’s DX Century Club and Worked All States awards. Confirmations are in the form of database records, electronically signed with the private key of the sender. This system simply matches database records but does not allow creation of pictorial QSL cards.
Even in the presence of electronic QSLs, physical 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.
Usage in shortwave listening 
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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. Standard frequency and time stations, such as WWV, will also send QSL cards in response to listeners reports. Other shortwave utility stations, such as marine and aviation weather broadcasters, may QSL, as do some Pirate radio stations, usually through mail drop boxes.
Usage in TV-FM and AM DXing 
QSL cards are also collected by radio enthusiasts who listen for distant FM radio or TV stations. However, with digital broadcasting TV stations are now less commonly heard on the air. AM radio stations may also reply to listeners, particularly if they report receiving them at a significant distance.
See also 
- Who invented the QSL Card?
- Ellen White, W1YL, ed. (1976). ARRL Ham Radio Operating Guide. Newington, CT: American Radio Relay League. p. 55.
- Eckersley, R. J, G4FTJ (1985). Amateur Radio Operating Manual (3 ed.). Potters Bar, Herts, UK: Radio Society of Great Britain. p. 32. ISBN 0-900612-69-X.
- The Radio Amateur's Handbook 1978. Newington, CT: American Radio Relay League. 1977. p. 653.
- "IARU QSL Bureaus". 2009-02-02. Retrieved 2012-11-11.
- http://www.eqsl.cc/qslcard/ : eQSL home page
- Gregory, Danny; Paul Sahre (2003). Hello World A Life in Ham Radio. New York: Princeton Architectural Press. ISBN 1-56898-281-X.
- A HAARP QSL card sent in 2008 on flickr.com
|Wikimedia Commons has media related to: QSL cards|
- Historical data on the early QSLs
- A very large QSL gallery, more than 8500 old and very old cards (French, machine translation into English available)
- Electronic QSL Card Centre
- American Radio Relay League Logbook of the World
- Martin Elbe's QSL-Pages, a QSL collection of broadcasting stations
- What information and where to print QSL cards, by Thierry, ON4SKY
- Primer on Q, Morse, RST and SINPO Codes by Thierry, ON4SKY
- Ham Gallery QSL Museum, a collection of QSL cards from around the world
- over 100,000 QSL gathered by Friedbert, DE0BRF
- SARL Electronic QSL service
- QSL Cards from the Past list of over 40,000 cards with over 2200 scanned cards on display including one from a young Coast Guard Sailor named Arthur M. Godfrey dated 1929.
- Arquivo Portugues de QSL Portuguese QSL Archive
- QSL Museum
- tarjetasQSL, Mendoza, Argentina