Can stations broadcast in HD only?

Can an AM or FM station ditch its analog signal and broadcast 10% or 100% power in HD? It would be suicidal, except for a few cases. Such as an AM station that mainly is heard through an FM translator. The AM could save 90% of its electricity by broadcasting only in HD. Or an FM station that wants to feed a bunch of translators with one signal, they could broadcast HD only and have 8 subchannels to feed 8 analog translators. Or an FM station in the middle of nowhere with an on-channel booster that serves 99% of its listeners. The main could broadcast in HD only, and the booster could broadcast in analog, eliminate the main/booster interference, and save electricity for the main transmitter that broadcasts to nobody.

Technically, it is possible and the Ibiquity system has a built-in migration path to all-digital. But it is not currently authorized by the FCC except on an experimental basis. There have been some limited experimental digital-only tests on the AM band, but none on FM that I know of. FM digital-only would occupy twice the bandwidth of a standard FM signal and would require a re-allocation of at least some stations in congested areas. There is also a fundamental problem with the "electricity saving" concept. HD requires a linear transmitter and although it broadcasts with less power the transmitter is far less efficient and the AC power requirements for HD are quite a bit higher, especially when you consider the additional cost of air conditioning (low efficiency means an HD transmitter emits a larger amount of heat). So no savings there at all.

Dave B.