The first use of radio control systems in models started in the 1950s with single channel self built equipment; commercial equipment came later. The advent of transistors greatly reduced the battery requirements, since the current requirements at low voltage were greatly reduced and the high voltage battery was eliminated. Crystal controlled superheterrodyne receivers with better selectivity and stability made control equipment more capable and at lower expense. Multi channel developments were of special use to aircraft, which really needed a minimum of three control dimensions, namely yaw, pitch and motor speed, as opposed to boats which only required two. As the electronics revolution took off, single channel circuit design was gradually phased out, and instead radios giving proportionally coded signal streams which a servomechanism could interpret. More recently, systems using Pulse-code modulation features have come on to the market, these provide a computerised digital bit stream signal to the receiving device, instead of analogue type pulse modulation. However, even with this coding, loss of transmission during flight has become even more common, mainly because of the increase in wireless use as a whole.