60s & 70s QSL Cards

QSL cards, generally the size of a standard US postcard, are used by amateur "ham" radio broadcasters, and are mailed between operators as a physical record of a successful two-way radio communication. Each QSL card is unique to its broadcaster, and usually has a distinctive front design as well as spaces on front or back to denote the time, date, radio frequency, mode of transmission, and a signal quality report for the interaction.