Abstract: An apparatus for blocking the transmission of echo signals in telephone communications circuits is disclosed. The apparatus employs a voice-activated switch in the transmit channel at each telephone terminal of the telephone circuit to block transmission of signals below a selectable threshold. Under all conditions where received speech signals are present at a telephone terminal, a higher threshold for the switch at that terminal is selected than would otherwise be used to block noise in the channel. This higher threshold is set above the level of the echo signals to prevent their transmission from that terminal by the switch.

Abstract: A solar cell coverslide, oversize to protect the cell against damage from radiation, is modified to have an edge portion configured to bend light incident on said edge portion inwardly toward an underlying solar cell. An adhesive fillet may be formed between the undersurface of the overhanging portion of the coverslide and the top edge of the solar cell to facilitate further the transmission of light striking the configured edge portion into the solar cell.

Abstract: A spatial diversity satellite communications system adapted to provide its own error control. The diversity communications system utilizes transmitting station selection or burst switching in the up-link and both probabalistic and algebraic error control in the down link to increase message accuracy and to overcome precipitation attenuation. Specialized multiple level decision demodulators are employed to exploit the inherent redundancy supplied by having available multiple signals embodying identical messages. Information is fedback, once the system is operating, and is used to select the optimum transmitter site. However, all available receivers are utilized and the received messages are statistically evaluated to accurately reproduce the received message.

Abstract: A digital voice switch for detecting speech signals in the presence of noise on a communication channel. The voice switch employs a threshold adjustment circuitry and three threshold detectors which include a speech detector, a noise detector and a disabling detector. The speech detector having a variable speech threshold level detects the presence of speech signals in the communication channel. The noise detector having a variable noise threshold level detects the presence of noise. The threshold adjustment circuitry, which is capable of providing rapid threshold adjustment, operates in conjunction with the noise detector to detect the noise level and to adjust the speech and noise threshold levels according to the level of the noise present in the communication channel. The disabling detector having a fixed maximum threshold level operates to disable the function of the threshold adjustment circuit while speech is present.

Abstract: A Space Division Multiple Access (SDMA) Communications satellite system which utilizes a pair of communications satellite relays having a communications link between them. Each satellite includes a plurality of receive spotbeam antennas which are selectively connected to a plurality of transmit spotbeam antennas by an on-board switching matrix under control of an on-board oscillator. Each spotbeam antenna communicates with a different geographical zone which includes one or more earth stations. Each station may communicate with all other stations in the system including those within the field of view of the spotbeam antennas aboard the other satellite. In order to maintain synchronization between the satellites, a designated reference station transmits a reference synchronization burst of four sequential unique words to the satellite within its field of view. The reference burst is related to the other satellite and back again to the first satellite where it is relayed back to the reference station.