Article: Early HDTV commercial experiments, such as NHK's MUSE, required over four times the bandwidth of a standard-definition broadcast. Despite efforts made to reduce analog HDTV to about twice the bandwidth of SDTV, these television formats were still distributable only by satellite.

Now answer this question: What kind of experiments required over four times the bandwith of a SDTV broadcast?
Early HDTV commercial experiments