Johnson Industries Ltd.


Technical Details

The radio choker system operates in the VHF band at a frequency of 72 to 76 MHz; each choker bell uses a microcontroller to decode transmitter data and actuate its spring-loaded latch mechanism. Transmitter range depends on the environment and typically falls between 30 and 60 metres; but, range will extend up to 300 metres under the skyline, as the steel cables on the yarder aid signal propagation. The transmitter operates on either 12 or 24 volt DC power.

Battery life for an individual choker bell depends on usage, and speed of the yarder. The choker bell draws no power when released, a few milliamps when set, and much higher current during setting and releasing. Setting and releasing both take under one second however, making the current draw when set and awaiting instructions from the transmitter the dominant source of battery drain; average battery life is 1.5 to 2 months.