In an analog world, operations on VHF channels (those between 2 and 13) could operate at power levels significantly lower than UHF stations (saving electricity costs), and still cover greater areas. The All-Channel Receiver Act of 1964 guaranteed that all new TVs must be designed to receive UHF channels, but the major networks were already well established. For digital transmissions VHF channels are very noisy in particular Low-VHF (channels 2–6). It is difficult to receive the signals without the standardized 30' outdoor antenna. Fewer than 40 full power stations in the USA are using Low-VHF channels since the mandatory digital conversion in 2009, and major network affiliates are mostly in large sparsely populated direct marketing areas where outdoor antennas are common.