Wireless anti-two-block or ATB systems eliminate the need for a wired connection between the ATB display and boom tip mounted two-block limit switch. The ATB switch on a wireless ATB uses batteries to power the ATB switch. The switch has an internal micro switch, and a wireless transmitter that can send a signal to the cab-mounted display. The RaycoWylie model R147 wireless ATB uses off-the-shelf AA batteries, which last up to a year and a half and are easy to replace.
A display mounted in the cab provides an audio and visual warning alarm when the crane's hoist block or hook gets too close to the boom tip. This is achieved by installing a two-block limit switch at the boom tip with a weight attached by a chain—the weight clamps around the hoist line above the hook block. When the block comes up near the boom tip, the weight is lifted, and the two-block switch closes. It instantly and wirelessly transmits a signal to the display in the cab. This causes the ATB alarm in the cab to alert the crane operator.
The advantage of the wireless ATB system is it does not need a spring tension reeling drum when used on a telescopic boom crane. The reeling drums are expensive and a part that tends to wear out over time. In addition, cranes used in tree cutting tend to break the cable on the reeling drum often, and this is expensive and disables the ATB alarm until its repaired. Wireless ATB systems have gained in popularity for their convenience and reliability.