A linearizing circuit is described which gives a nonlinear relation between an input and an output signal of the circuit. Such a circuit can be used to compensate for the nonlinearity in, for example, a frequency modulator. The circuit includes a nonlinear element, preferably a PIN-diode connected in a voltage divider to provide a biasing current to the element. An attenuating and an amplifying circuit are connected to the input and to the output, respectively, of the circuit. By varying the values of the attenuation/amplification and the value of the operation point of the element, the nonlinearity of the circuit can be varied.
A transmitting earth station for a satellite communications system in which the channel capacity of a two-carrier-per-transponder transmitter is greatly enhanced. The transmitting station is provided with an equalizer at the input to the high power amplifier (HPA). The transfer function of this equalizer assists in the reduction (in the first order approximation) of the intelligible crosstalk due to the non-linearities of the HPA, the travelling wave tube amplifier (TWTA) and the input transponder multiplexer. With the intelligible crosstalk reduced, the input backoff of the transponder TWTA may be reduced from -12dB to -6dB, which increases the channel capacity in the order of 500 channels.
A hand held, short range FM radar device is provided employing a unique tracking circuit and a predistortion circuit to linearize the sweep function to a Gunn oscillator which produces the rf signal. A parabolic generator comprising a linear operational amplifier and passive elements connected thereto is used to shape the saw tooth sweep signal to the Gunn oscillator. The output is directly read out on an LED display; an audio signal is also produced whose frequency is a function of target distance.
Several embodiments are disclosed of a modulation equalization network associated with a phase locked loop to achieve frequency independent modulation of the VCO. The equalization network is disposed to introduce the modulation signal into the control loop ahead of the loop filter but after the phase detector output. The interposed equalization network requires only a single input port to achieve a flat modulation response thereby lending itself to a modular implementation. The modulation processing is performed totally outside the phase locked loop. The network serves to provide a boost to low frequency signals from the modulation source using an integrator network while providing a high frequency response that is essentially the inverse of the phase locked loop filter response.
A single input wideband modulation system for a phase locked loop is achieved by interposing the inverse analogue of the closed phase locked loop transfer function between the modulation source and the VCO modulation input. A first branch of the interposed circuit directly passes high frequency signals from the modulation source to a summing device tied to an input of the VCO. A second branch of the interposed circuit boosts low frequency signals and blocks high frequency signals recieved from the modulation source and passes such signal to the summing device where signals from the first and second branches are summed to permit wideband modulation of the VCO. All the modulation processing is performed outside the phase locked loop.
A modulatable oscillator for radio frequencies is disclosed in which the single resonant tank includes a tightly coupled varactor diode for wideband modulation and frequency control. Nonlinearities introduced by the varactor diode are compensated by predistortion of the modulated signal yielding a predetermined modulation characteristic which is maintained over temperature.
