At first, radio stations depended on advertising their own products such as radio receivers rather than commercials:

Name: At first, radio stations depended on advertising their own products such as radio receivers rather than commercials:
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In the early days of radio, advertising time was mainly used for promoting the station's own products, such as radio receivers or accessories, rather than airing commercials for other companies.

At First, Radio Stations Depended on Advertising Their Own Products