“Obviously it is a waste of valuable spectrum space to use two frequencies to bring the same material to the same location.”
Believe it or not, it was the Federal Communications Commission in 1965. A year earlier agency ruled that no FM station broadcasting to a city of more than 100,000 people could devote more than half of its average program week to content copied from a co-owned AM station streaming to the same area. The Order went into effect a year later. I’ve got audio on the impact of this decision in one of our recent podcasts. It was a very good intervention for FM and obviously stands in stark contrast to the FCC’s recent decision to provide opportunities for AM stations to procure translator repeater stations so as to rebroadcast their stream on the FM band. Talk about turning the clock back half a century!
Anyway, I’ve been looking for the original Order for some time, to no avail. But I have found a summary of the decision on the FCC’s Audio Division engineering page, which includes pdfs of every Annual Report going back to 1935. So here’s the text of the summary from the Commission’s 1965 Annual Report:
“Hitherto, there has been no restriction on the presentation of identical programs on commonly owned FM and AM stations, and many AM-FM station combinations present the same material at the same time during their broadcast hours, using the FM station as an adjunct of the AM.
Obviously it is a waste. of valuable spectrum space to use two frequencies to bring the same material to the same location. This has been permitted in the past because it provided an easy and inexpensive start for FM broadcast. However, with the mounting number of FM sets and growing interest in the medium and competition for channels especially in the larger cities, the Commission in 1963 proposed a rule limiting the extent to which this essentially wasteful practice could be engaged in (docket 15084).
It culminated on July 1, 1964, with the adoption of a rule providing that no FM station in a city of over 100,000 population can devote more than 50 percent of its average broadcast week to duplication of the programming of a commonly owned AM station in the same local area. “Duplication” is defined to include presentation of the same material simultaneously or within 24 hours before or after it is presented on the AM station. This rule was affirmed in March 1965 but the effective date was postponed from August 1, 1965, to the following October 15.
It applies to cities of over 100,000 population because FM channels in these cities are scarce and in demand, and it is unreasonable to permit a licensee under these conditions to use two channels for the same program. The Commission believes that this non duplication requirement will further spur the development of FM. Permitting 50 percent duplication will still permit an AM-FM broadcaster to duplicate news and considerable other programming if he wishes to do so.
The Commission provided that requests for exemption could be filed and 109 such requests were received up to June 30, 1965. The following month it granted 106 exemptions until December 31, 1965, and three requests for temporary exemption until April 15, 1966.”
You can read the pdf yourself here (see page 118).