Abstract: A remote control system capable of utilizing manually encoded signals is disclosed. The system is particularly suitable for use in the logging industry because it is capable of utilizing standardized whistle signals for both remove control and audible signalling purposes. The system includes a transmitter for transmitting a manually encoded signal. The control signal is received by a receiver and is decoded by a decoder that reduces the manually encoded signal to a digitized signal. The digitized signal is compared with a set of reference digitized signals, and if a match is found, a corresponding output control signal is applied to a controlled device such as a yarder.

Abstract: An improved decoder for providing a decoder output signal when a tone signal contains frequencies that are sequentially within a predetermined passband surrounding first and second detection frequencies f.sub.1, f.sub.2. A tone signal is mixed with a reference signal which alternates, at a multiplex frequency, between sine and cosine signals, each being at a predetermined reference frequency which is less than the multiplex frequency. A tone switching logic circuit normally maintains the reference frequency at a value substantially equal to the frequency f.sub.1. The mixed signal is coupled through a demultiplexer to respective inputs of first, second, third and fourth low pass filters, each of which has a cut-off frequency which is one-half of the decoder passband. The respective outputs of the filters are coupled through a multiplexer to a squarer.