Abstract: A communication network for an area such as an underground mine. A plurality of cascaded base stations (13) are serially interconnected in a ring structure (11) to form a network backbone. One of the base stations (13) at one end of the network backbone forms a network controller (15) for controlling the network. A plurality of portables (17) are adapted for communication with any of the base stations via a common air interface. A backbone network protocol (19) is provided for communicating between the network controller (15) and all of the base stations (13) and between the base stations (13) along the network backbone themselves. A common air interface protocol (21) is provided for communicating between a portable (17) and a base station (13). The other base stations (13) function as slaves relative to the network controller (15).

Abstract: A digital frequency detector (10) and method for digitally detecting arbitrarily small phase changes between a signal waveform and a reference waveform. Both the reference waveform and the signal waveform are sampled at a rate related to the clock frequency fc, and separately fed into two arrays of simple frequency detectors (12, 14). Each simple frequency detector in each array has a different starting phase with respect to the reference waveform and the signal waveform respectively. Phase slips between the reference waveform and the sampling frequency and phase slips between the signal waveform and the sampling frequency are measured by the detector arrays (12, 14). These phase slips, called “slip events”, are combined in circuit (16) which produces an output indicative of phase slips between the reference waveform and the signal waveform. Using this phase slip information, the instantaneous frequency difference between the signal and reference waveforms can be determined.

Abstract: A Steered Frequency Phase Lock Loop (SFPLL) comprises a phase loop that functions like a normal phase locked loop (PLL) and locks to the input signal, and a frequency loop that uses a reference frequency to influence the phase loop and effectively confines the output frequency of the phase loop and the SFPLL to be in a range of frequencies close to the reference frequency. The reference frequency is chosen to be very close to the input signal frequency that it is desired the SFPLL lock to. The SFPLL comprises a phase detector (10), a frequency detector (22), first and second gain components (12, 24), first, second and third filter components (14, 18, 26), a summer (16) and a voltage controlled oscillator (VCP)(20). By a judicious choice of the gains in the phase and frequency loops the SFPLL can be designed so that the range of frequencies to which the SFPLL will lock can be confined to an arbitrarily small region around the reference frequency (.omega.'.sub.r).

Abstract: A tool for measuring the extent of decay in a wooden object, comprising an elongated probe adapted to be inserted in an inspection hole drilled in the wooden object. The tool has at least one barb protruding therefrom adjacent to one end of the probe. The barb is designed to engage a side wall of the inspection hole so as to shear wood fibers in the side wall as the probe is withdrawn. There is indicator mechanically coupled to the probe for measuring the amount of pull-force required to shear the wood fibers in the inspection hole. The indicator includes a deflector mechanically connected to the other end of the probe and adapted to provide a measurable deflection as the pull-force required to shear the wood fibers increases. In use, when the pull-force exceeds a predetermined value, the indicator provides an indication of a transition within the wooden object from decaying wood to sound wood.

Abstract: An apparatus and method are provided for supporting a plurality of virtual channel (VC) connections within a single virtual path (VP) in a digital communications network operating in the Asynchronous Transfer Mode (ATM). The apparatus (56) is combined with the cross-connected part of a conventional VC switch (54) to form a Data Switch (40). A VP switch (42) switches and terminates incoming bandwidth-resourced VPs on lines (48), some of which are carrying non-bandwidth-resourced VCs and switched onto lines 50 on the output side of VP switch 42. VPs on lines (50) are switched and multiplexed by the Data Switch (40). Buffers (66) store cells and a VP rate server. The buffers (66) are significantly larger than in a conventional VC switch to enable smoothing of data flow peaks associated with data flowing from multiple bandwidth resourced VP tributaries into single resourced VP tributaries. Despite the large buffers in the Data Switch (40) congestion may result when data bursts occur on several converging streams.