Abstract: A Cartesian loop transmitter for transmitting baseband signals is disclosed. The disclosed Cartesian loop includes a forward path having a first input for receiving the baseband signals and a second input and a feedback path having an input from the forward path. The forward path including an upconverter to upconvert the input signals to a signal to be transmitted, an attenuator having selectable attenuation and a plurality of power amplifier stages. The feedback path including a pin diode attenuator having selectable attenuation and a downconverter to downconvert the input from the forward path. The feedback path provides an error signal indicative of the non-linearity of the forward path to the second input of the forward path.

Abstract: The present invention relates to a radio receiver, particularly to a receiver for use in single-frequency applications, such as GPS, and to a frequency generator, which may be used in such a radio receiver, or elsewhere. The frequency generator comprises a tuned circuit connected between the emitter of the transistor and ground, such that a voltage signal at the basic frequency appears on the emitter terminal of the transistor. This arrangement has the advantage that the two frequencies appear on separate ports, and provides a radio receiver including radio receiver circuitry for connection to digital signal processing circuitry, reducing the complexity of the overall circuit. Additionally, there is a radio receiver wherein separate first and second local oscillator signals are generated from the terminal of s single transistor, avoiding the need for cascade multiplication stages, again reducing the size and complexity of the overall circuit.

Abstract: The invention provides methods and apparatus for substituting a reference spread spectrum signal for a pilot tone or providing a reference spread spectrum signal where no pilot tone has been used. The invention has particular relevance when a large number of input channels are required for a broad band linear amplifier and when an omni-directional antenna is required for a repeater which may be prone to instability.

Abstract: Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of the amplifier 4 by comparison in a subtractor 11 with its input and the error signal is combined in a coupler 17 with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by means of components 24 and 25 in a multi-channel input and in the error signal by means of components 13 and 14. These components receive control signals from feedback networks 18' and 20' which each process two of three input signals from: couplers 34, 36 before the subtractor 11, a coupler 22 which passes the error signal and a coupler 21 after the coupler 17.

Abstract: Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of an amplifier by comparison in a subtractor with its input and the error signal is combined in a coupler with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by two groups of adjustment means, one group in a multi-channel input path and one group in the error signal path. These groups receive control signals from respective feedback networks which each process two of three input signals from: couplers before the subtractor, a coupler which passes the error signal and a coupler situated after the coupler which combines the amplifier output signal and the error signal.