Abstract: A communications system is disclosed for spectrum sharing of a microwave point-to-point system and a PCS system. The invention comprises a microwave communications system. This system includes a transmitter for transmitting a first signal and a second signal. The first signal and the second signal are oppositely circularly polarized electromagnetic waves within a predefined frequency range. The system also includes a receiver for receiving the first and second signals. In the preferred embodiment of the present invention the receiver may further include a first microwave receiver for receiving the first signal. It would then include a second receiver for receiving the second signal. The receiver would also include signal combining circuitry for combining the first signal and the second signal to generate a composite signal. It would then include a signal comparator to generate a comparison signal by comparing the average value of the amplitude of the composite signal with a predetermined value.

Abstract: A cellular telephone system is described of the type wherein a plurality of contiguous cells, each having an assigned set of identification codes, are arranged with means for maintaining continuous communication with mobile telephones moving from cell to cell. The system allows multiple access by including means for assigning at least one of the in the assigned set of identification codes to more than one mobile telephone. A unique identification code is assigned to a mobile telephone located in the cell. A signal having a unique identification code is generated for identifying the mobile telephone. The signal is coupled to the zones. A combiner is also provided for combining signals from all of the zones in the cell. A receiver is coupled to the combiner for retrieving the signals having the code.

Abstract: This invention is a multiple-frequency signal generator apparatus and method primarily for simulating a cell site interference environment for electromagnetic communications systems. The generator can produce a plurality of frequencies having a frequency-spacing of d cycles per second. The invention comprises a single frequency multiplier, at least three oscillators and two mixers for providing a multitude of frequencies closely spaced about a carrier frequency. The simple design and components avoid complexity and save costs.

Abstract: A mobile communications system uses a communications satellite and a Mobile Telephone Switching Office (MTSO) and communicates with mobile units via the satellite. A cell site has a co-located cell site converter which converts satellite signals to signals for the MTSO and vice-versa. Remote converter sites communicate with the satellite and with the mobile units in given geographical areas. A single satellite link is sufficient for adequate RSA service. Frequency and phase differences among signals from the remote sites to the satellite are synchronized to avoid frequency- and phase-drift.

Abstract: A combustion air heating system includes both an air heater for preheating the combustion air by heat exchange with flue gases and an air preheater for preheating the combustion air prior to entry into the air heater. The air preheater operates by heat exchange between the combustion air discharge from the air heater and a bypass stream of combustion air located upstream of the air preheater. The amount of combustion air flowing through the bypass duct is controlled so that the temperature in the air heater does not fall below the dew point of the acid gases present in the flue gas.