Abstract: A clear channel detector for use in a binary digital data transmission system in which collisions are possible between simultaneously transmitting stations all connected to a common transmission medium. The detector receives the output from each of a pair of different binary symbol detectors in the station receiver. The voltage difference between the binary symbol detector outputs is amplified, and the resulting bipolar voltage is converted to an absolute amplitude. After further amplification, a threshold adjustment is provided at a trigger subcircuit having at least one output signal indicating the presence of a clear transmission channel which is not presently in use.

Abstract: The average frequency and sweep rate of a chirped oscillator are automatically digitally controlled for correction of long term drift. During each of successive swept-frequency chirps, the swept frequency output of a voltage-controlled oscillator is counted and the overflow time of the counter is utilized to control the average frequency. A second counter counts the chirp frequency in a first direction during a first preset period at the beginning of each chirp and counts the chirp frequency in a second and opposite direction during an identical preset period later in the chirp, to provide an underflow transition related to the slope of the chirped frequency signal. Digital circuitry for synthesis of the chirped oscillator frequency ramp signal, and for correction of the average frequency and slope thereof responsive to the first and second counter transitions, is utilized.

Abstract: The operating frequency of a multi-station power-line-carrier-communications system is automatically changed to avoid narrowband interference. Any one of the plurality of stations in the system can initiate a command to shift operating frequency, when the communications signal reception degrades below a predetermined criterion. An interfering signal itself can initiate a shift in operating frequency when the characteristics of the interfering signal are sufficient to deteriorate communications on an existing operating frequency.

Abstract: The starting frequency and sweep rate of a chirped frequency-shift-keyed oscillator are automatically controlled for correction of long-term drift. The substantially linear swept frequency output of the oscillator, during each of a successive multiplicity of swept frequency chirps, is counted and the count converted to an error signal utilized to control an appropriate potential in the oscillator circuit. The initial frequency is monitored, where the swept frequency range is small compared to the initial frequency, by counting the number of cyles during a chirp period in obtaining a first error signal from the total cycle count. The frequency-chirp ramp rate is monitored by counting the number of cycles during an initial portion, e.g.

Abstract: A method for transmission of digital data utilizes a carrier frequency offset in a first frequency direction for a first binary condition, and offset in a second frequency direction for the remaining binary condition, at the start of a bit time interval. The carrier frequency is swept in a preselected frequency direction during each bit time interval, to produce a chirped frequency-shift-keyed waveform in the frequency domain, for transmission of each bit of binary data. Frequency-shift-keyed demodulation is utilized at a receiving end, with the receiver synchronized to the transmitter bit time interval, to recover the transmitted digital data. Apparatus for data transmission using this chirped frequency-shift-keyed modulation waveform is disclosed.

Abstract: In a digital data communications system having a plurality of slaved data transceivers transmitting data to, and receiving data from, a master station, the master station classifies a received signal, in each of a multiplicity of bit time intervals, as one or the other of the pair of binary signal states. The received binary signal state is echoed to all of the slaved stations, to cause those stations which did not previously transmit that binary state to cease transmitting data. Those slave stations which transmitted the echoed previous bit binary state then transmit the next bit of data, which is again echoed. Slaved stations receiving bit echoes which are different from the previous bit sent will know that there has been a collision and that the master station did not receive their bit of data, whereby the number of slave stations transmitting is reduced, in successive bit time intervals, until only one slave station remains transmitting.

Abstract: A system for providing perimeter security, intra-building communication and control functions, utilizes a pair of single wire loops placed about the periphery of the building, and spaced from one another. At least one facilities unit, for fire detection, appliance control and the like functions, has the powering battery thereof series-connected in one of the perimeter loops, and with that loop being connected to battery trickle-charging circuitry. Each of the unit batteries is bypassed by a capacitive element, selected for the frequency, partly determined by the capacitance between the pair of loops, of an oscillator for detecting proximity of intruders adjacent to the building periphery. The proximity-detection oscillator includes a transformer for coupling a data transceiver to and from the remaining loop, whereby voice and/or digital communications may be modulated upon a magnetic field extending throughout the interior of the building for communications to and from independent units therein.