Two amateur radio call books: RSGB Amateur Radio Call Book First Edition, published by the Radio Society of Great Britain, British, Autumn 1951; Radio Amateur Call Book Magazine Vol.19. (worldwide), unknown publisher, Summer 1938.
Call books like these provide listings of active call signs, the series of letters and numbers that identify radio stations. They are used by amateur radio enthusiasts. The 'Radio Amateur Call Book Magazine vol. 19' dates from summer 1938, while the 'RSGB Amateur Radio Call Book' is British and dates from autumn 1951.
Science Museum, Information Age Gallery: Broadcast