Abstract: A millimeter wave link provides a means for easily transporting multiple high speed data channels, in excess of 100 Mb/s, a distance of up to 10 km, without requiring elaborate modulators and demodulators. This invention also provides fast setup, versatility, and is portable, which makes it desirable for field use. In addition, it can be set up for long term high speed data collection in a virtually permanent environment. The unidirectional link of the present invention is intended for use in experimental data collection systems, where portability, ease of setup and high speed data transfer are required. University environments as well as independent research and development institutions can benefit significantly from its use.

Abstract: A communications station (10) couples a bidirectional input-output signal path (16') to two unidirectional signal paths; a transmit signal path (12') and a receive signal path (14'), using a controllable hybrid (20). A feedback control system in the station minimizes the amount of transmit signal appearing at the receive output port (24) of the hybrid (20). The control system spreads the spectrum of a pilot signal (40) by means of a biphase modulator (46) and a pseudorandom generator (42) to produce a spread-spectrum pilot, which is added, in a summer 30, to the transmit signal. The spread-spectrum pilot signal covers the bandwidth of the information signal, and is reflected in an amount and with a phase which depends upon the relative impedance presented to the hybrid (20) by the bidirectional signal path (16').

Abstract: Apparatus for electronically steering a null in a total radiation-reception pattern provided by a set of angularly disposed (preferably substantially-orthogonally-positioned RF) antennae, uses: first and second N-bit binary attenuator subsystems for modifying the amplitude of a signal provided by an associated one of the pair of antennae, responsive to an associated one of first and second control data signals; a set of look-up tables, receiving null-angle input data, provide the first and second signals as the sine and cosine, respectively, of the input null-angle; and the output of the first and second attenuator means are then combined to provide an output signal in which contributions arriving at the set of antennae substantially at the null angle are substantially reduced. The signal combiner may include at least one polarity reversal circuit, possibly including a transformer and/or switch means, to accommodate nulling to all four quadrants of a full circular response pattern.

Abstract: A frequency shift keying system for transmitting a signal which is a function of supplied data, includes first and second frequency generators producing first and second frequencies which differ in value by an amount which is a function of the maximum baud rate of the data. A counter is responsive alternately to one and the other of the two frequencies supplied thereto as a function of the data values for alternately counting up and down between values which differ by some given amount. The counter output in analog form is the transmitted signal. This system is particularly adapted to minimum frequency shift keying.

Abstract: A photon energy activated PIN diode is reverse biased by a continuously supplied direct current voltage. The PIN diode is rendered conductive for passage of a radio frequency input signal when it is illuminated. Continuous illumination of the PIN diode is not required for conduction such that illumination may be pulsed on and off while the diode remains conductive.

Abstract: An apparatus for testing the crosspoints of an RF switching matrix injects a test signal having the characteristics of noise into the matrix. The test signal recovered from the matrix is mixed with a frequency-swept signal and the difference signal is applied to a bandpass filter. The filter provides a window through which all of the frequency-shifted components of the recovered signal pass during the period of the frequency-swept signal. The total energy of the components in the window is continually monitored during the sweep period. A comb generator provides the test signal having a multiplicity of substantially equal amplitude components, uniformly spaced over a selected frequency spectrum. The frequency-swept signal is provided by a VCO having a sawtooth waveform input voltage. The amplitudes of the test signal components are sufficiently low that if coupling occurs between the test signal and a configured external antenna, the resulting transmission is virtually indistinguishable from noise.

Abstract: An RF switch employing a PIN diode as the switching element includes a first bias circuit providing forward dc current through the diode to enable RF transmission therethrough, and a second bias circuit providing reverse dc voltage across the diode to disable RF transmission through the switch. Status circuitry monitors the switch for failure modes of the diode, and control circuitry selectively enables the bias circuits. A short circuit failure of the PIN diode is indicated by the flow of reverse current in the second bias circuit in excess of the diode leakage current. Under this condition, the reverse current is latched by a thyristor in the second bias circuit and the status circuitry generates an alarm signal to the control circuitry inhibiting further selection of the first bias circuit. Optical couplers provide electrical isolation of the first and second bias circuit from the control and status circuitry.

Abstract: A frequency division multiplex communications system groups a plurality of communications terminals such that they are coupled onto the communications bus at a single node. Each terminal comprises a fixed-frequency receiver, a frequency-agile transmitter, or both. Each receiver in the system is tuned to a different carrier frequency. Furthermore, the receivers grouped at each node are tuned to carrier frequencies within narrow frequency bands, typically within 2.5 percent of a center frequency, with no overlap between the frequency bands of the several groups. Using this configuration, only one receiver amplifier, one preselector bandpass filter, and one transmitter low pass harmonic filter are required for the plurality of terminals within the grouping.

Abstract: An apparatus for selectively switching between either of two RF clock signal sources utilizes field effect transistors (FET's) as the switching elements. The FET's are driven at their respective base electrodes by complementary signals from open collector logic gates to provide signal source selection. In the event of loss of power to the RF switch, the energy from the RF signal passing through the previously selected switch path provides a positive (enabling) bias to the FET's in that path and a negative (disabling) bias to the FET's in the other path, thereby maintaining the selected path. The open collector logic gate circuits appear as open circuits when power is lost. During normal powered-on operation, the selection logic overrides the RF signal energy biasing circuits.

Abstract: A passive, single cable, local area network system includes two directional couplers at each cable tap to provide bi-directional communications for each communications terminal. Each coupler introduces some amount of signal power loss through the cable such that the signal power level between any two communicating terminals depends on the cable distance between them, measured in number of intervening cable taps. Selectable attenuators are provided between the directional couplers and the corresponding communications terminals to virtually equalize the signal power level between any two terminals. The value of attenuation is selected according to a relationship including the number of cable taps in the system, the signal power loss along the cable introduced by each directional coupler, and the ordinal number of the corresponding terminal from the cable termination in the direction toward which the terminal's directional coupler communicates.

Abstract: A frequency time standard monitoring system includes three highly accurate standards of substantially identical frequency. These three standards are compared in pairs by three monitoring apparatus. Each such apparatus includes a fine window detector for determining the phase relationship between the two applied frequency standard clock signals, and a phase shifter responsive to the fine window detector for shifting the phase of one of the signals until the signals are phase aligned. When this occurs, the fine window detector is disabled and a coarse window detector monitors the two clock signals to ensure that the clocks do not drift beyond tolerable limits. The output signal of the coarse window detector is applied, along with the corresponding signals from the other two monitoring apparatus, to a select logic which determines which standard should be on-line in the event of a fault detection.

Abstract: A lossless, bi-directional bus tap for connecting peripheral devices to a common bus. The tap comprises first and second combiner/divider (C/D) networks each having a first input/output (I/O) port which are connected to the two ends of an interruption in the common bus and N second ports with Y db isolation between the I/O port and any of the N second ports and X db isolation between any two of the N second ports. The tap is responsive to an input signal supplied to the I/O port or to input signals supplied to the N second ports to produce, respectively, divided signals on the N second ports and a combined signal on the I/O port. Also provided are two Z db gain amplifiers connected in reverse direction of amplification between first ports of the N second ports of the two C/Ds and between second ports of the N second ports of the two C/Ds, where X>Z and Z.congruent.2Y, and logic bi-directionally connecting a peripheral device to third ports of the N second ports of the two C/Ds.

Abstract: Each of a plurality of circuit paths between a common input terminal and respective output terminals includes a switching device which can be switched between a high and a low impedance state. When a device in one path is switched into its low impedance state in response to a path selection signal, the devices in the remaining paths automatically are switched to their high impedance state in response to a portion of the signal to be passed through the path with the low impedance device. In this way, one of the circuit paths may be selected for coupling the input terminal to a selected output terminal and all other circuit paths are automatically blocked.

Abstract: A transceiver provides data collision detection and avoidance in a contention-formatted, FDM communications network using FSK modulation. Locally-generated baseband data is compared to recovered baseband data received from the system bus. A failure to compare indicates that there has been a data collision. The wide disparities in amplitude between locally-generated FDM signals and signals received from the bus are accommodated by a signal splitter which provides greater attenuation of the local signal than the generally weaker bus signal, and by the use of logarithmic amplifiers which generate relatively constant output levels for a wide range of input signal amplitudes. Collision avoidance is provided by monitoring the bus signal demodulators for data activity, and by inhibiting the local transmitter when such activity is detected, subject to an override during transmission by the local station.