Abstract: A tunable resonant system includes an electric element, and a core having a controllable parameter that determines the resonant frequency of the system. In order to tune the resonant system to a desired frequency, a low power, narrowband signal is applied at a selected frequency to the electric element. The reflected or transmitted power is measured and the value of the controllable parameter adjusted to vary the resonant frequency of the system in a closed loop until the reflected power is at a minimum.

Abstract: A packet data communication system includes a control station and a plurality of mobile terminals that communicate on demand with the control station over a wireless link. The control station has a data port for receiving data packets destined for the terminals, an arrangement for generating a plurality of data channels for carrying the data packets, and an arrangement for assigning the data packets destined for a particular terminal to one or more of the data channels. A control channel carries control information pertaining to the data channels. The channels are transmitted to the mobile terminals as an r.f. signal. The terminals have a receiver for receiving the r.f. signal, an analog-to-digital converter for digitizing the received signal, and a buffer for storing the digitized received signal. The terminals continually monitor the control channel to extract control information.

Abstract: In a method of providing an interactive broadcast service, broadcast signals are transmitted via a wideband satellite link to end users. Return signals are received from the users transmitted over a narrowband satellite link separate from the first link. The return signals allow users of the service to send commands back to the base station to request specific services.

Abstract: A low profile antenna with high gain at low elevations suitable for satellite communications consists of a helical loop with turns tightly spaced to provide a strong coupling therebetween. The pitch is typically 1 to 2 degrees. The helical loop behaves like a travelling-wave loop antenna.

Abstract: A system for disseminating information over a wide area network includes a central caching unit for storing data to be made available over the wide area network. Local access give users access to the wide area network. Distributed caching units associated with the local access nodes for store cacheable material. A satellite communications system establishes satellite communications between the central caching unit and the local caching units for the transfer of cacheable material from the central caching unit to the local units. A router at the local access nodes routes packets from users to a destination address. The router includes local routing tables containing the addresses of material cached at the associated local node and responds to routing requests for locally cached material by directing the requests to the local cache.

Abstract: An integrated dual-mode antenna including a quadrifilar antenna and a collocated monopole antenna. The integrated antenna is compact and unencumbered by signal blockage or isolation problems.

Abstract: A two-way satellite communications system includes an Earth station communicating with a plurality of remote terminals using a network access protocol that facilitates low power consumption by the terminals. The earth station generates forward link TDM packet data transmissions on one or-more satellite channels, and detects, despreads and decodes multiple concurrent return link slotted CDMA packet transmissions on one or more satellite channels. It communicates through a wired connection with a packet processing center which ultimately both delivers return link packet data to end-customers and receives forward link packet data from end-customers. The remote terminals receive, process and act upon forward link TDM transmissions on one or more satellite channels, and generate slotted spread spectrum CDMA transmissions on the return link on one or more satellite channels.

Abstract: A method is described for transmitting a signal over a wireless communications channel, the communications channel being common to primary and secondary communications systems that have at least partially overlapping areas of coverage. The primary system has a low duty cycle and transmits random bursts having a characteristic first duration. The method involves transmitting bursts on the secondary system, which have a duration at least equal to three times the first duration and contain forward error correcting codes to permit data contained therein to be recovered in the event of a collision with a burst on the primary system. The bursts on the secondary system have an intensity sufficiently below the intensity of the bursts on the primary system to avoid interference therewith.