This article is from the Old Time Radio FAQ, by Lou Genco webmaster@old-time.com with numerous contributions by others.
Two ways: Many networks used telephone lines to carry the show
from the studio to transmitter sites. The show was done live at least
twice - once for the East coast, once for the West. After Bing Crosby
spearheaded the introduction of recorded shows (about 1948), the East
coast show was recorded for later telephone transmission to the West
coast.
 
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