Letterfrack (Leitir Fraic in Irish from Leitir meaning rough hillside and perhaps from the Old Irish word Fraig meaning woman or fraoch meaning heather) is a small village in Connemara in Ireland founded by the Quakers in the mid-19th century. It is situated 15 km north-east of Clifden on Barnaderg Bay and lies at the head of Ballinakill harbour. The visitors centre for Connemara National Park is here.
Letterfrack had a reformatory industrial school which closed in 1974.
Letterfrack was selected by Marconi as the location for the transatlantic wireless receiver station for his new duplex transatlantic wireless service. At about the same time, he built a nearly identical receiver station on the other side of the Atlantic at Louisbourg, Nova Scotia. Beginning in 1913, eastbound messages were sent from his Marconi Towers, Nova Scotia high power wireless station to Letterfrack; while westbound messages were sent simultaneously from the Clifden high power wireless station to Louisbourg. The Letterfrack station was closed and the service was transferred to a modern receiver station in Tywyn, Wales after his Clifden station was destroyed in 1922 during the Irish Civil War. Duplex operation -- initially developed by Marconi at Letterfrack -- quickly became a standard practice for commercial and military radiotelegraph communication.