By 1954, all U.S. networks had regained control of their programming, with higher advertising revenues: ABC's revenue increased by 67% (earning $26 million), NBC's went up by 30% ($100 million) and CBS's rose by 44% ($117 million). However that year, ABC had only 14 primary affiliates compared to the 74 that carried the majority of CBS programs and the 71 that were primarily affiliated with NBC. Most markets outside the largest ones were not large enough to support three full-time network affiliates. In some markets that were large enough for a third full-time affiliate, the only available commercial allocation was on the less-desirable UHF band. Until the All-Channel Receiver Act (passed by Congress in 1961) mandated the inclusion of UHF tuning, most viewers needed to purchase a converter to be able to watch UHF stations, and the signal quality was marginal at best even with a converter. Additionally, during the analog television era, UHF stations were not adequately receivable in rugged terrain. These factors made many prospective station owners skittish about investing in a UHF station, especially one that would have had to take on an affiliation with a weaker network.