Abstract: A transmission line balun comprising a tubular ferrite having a longitudinal passageway concentrically positioned over a conductive sleeve having a longitudinal passageway. The end of a coax feeder is positioned in the longitudinal passageway of the sleeve and the sleeve is grounded at its proximal end to the shield of the coax cable. The sleeve buffers the effects of the parasitic line caused by using ferrite in a balun.

Abstract: A broadband impedance matching circuit using high pass and low pass filter sections alternatingly cascaded together to yield considerably broader band matching than two high pass sections or two low pass filter sections. By alternating the high pass filter sections with the low pass filter sections, significantly fewer elements are required for a given result than non-alternating prior art cascaded filter sections. Consequently, the alternating filter sections according to the present invention significantly improves the return loss at increased bandwidths.

Abstract: A transmission line balun comprising a tubular ferrite having a longitudinal passageway concentrically positioned over a conductive sleeve having a longitudinal passageway. The end of a coax feeder is positioned in the longitudinal passageway of the sleeve and the sleeve is grounded at its proximal end to the shield of the coax cable. The sleeve buffers the effects of the parasitic line caused by using ferrite in a balun.

Abstract: A method and circuit for detecting and reducing the impedance mismatch between the directional coupler and the antenna of an RF communications system exposed to externally generated RF signals. The impedance mismatch is detected by the quadrature multiplication of the signal passing through a directional coupler in the forward and reverse directions with the detection being enhanced by the use of a forward direction signal substantially devoid of externally generated RF signal components.

Abstract: A circuit for reducing the effect of acoustic and electrical feedback in duplex "hands free" telephone sets. The circuit uses relatively simple and inexpensive gain control circuits and expanders to reduce the effects of feedback by controlling the gain of a transmitted signal in inverse relationship to the strength of a the received signal.

Abstract: A communications system including a central station and a plurality of remote stations, for example, a mobile telephone system, is disclosed in which communications channel establishing signalling transmissions between the central and remote stations are conducted in a clear (unenciphered) mode and subsequent voice transmissions between the central and remote stations are conducted in a secure (enciphered) mode. Each remote station has a unique code assigned thereto which is used by it to at least decipher incoming enciphered voice transmissions from the central station and by the central station to encipher outgoing voice transmissions to the remote station. The unique code may also be used by the remote station to encipher outgoing voice transmissions and by the central station to decipher incoming voice transmissions from the remote station.

Abstract: A communications system including a central station and a plurality of remote stations, for example, a mobile telephone system, is disclosed in which communications channel establishing signalling transmissions between the central and remote stations are conducted in a clear (unenciphered) mode and subsequent voice transmissions between the central and remote stations are conducted in a secure (enciphered) mode. Each remote station has a unique code assigned thereto which is used by it to at least decipher incoming enciphered voice transmissions from the central station and by the central station to encipher outgoing voice transmissions to the remote station. The unique code may also be used by the remote station to encipher outgoing voice transmissions and by the central station to decipher incoming voice transmissions from the remote station.