Abstract: A mixer circuit has a first filter connected between a local oscillator terminal and a node and another filter connected between a RF signal terminal and the node. A first circuit path extends from the node through a first diode to a first tuned circuit which can be connected to an input terminal of a balanced-to-unbalanced converter. A second circuit path extends from the node through an oppositely disposed diode which is connected to another tuned circuit which can be connected to another input terminal of the balanced-to-unbalanced converter. The diodes alternately conduct in response to opposite half cycles of the local oscillator signal and the RF signal to generate a variety of mixing components. The tuned circuits preserve the desired output signal and attenuate the other mixing components.

Abstract: Microprocessor (MPU) controlled voltage controlled oscillator (VCO) linearization circuitry locks the VCO at desired low, center and high frequencies (F.sub.1, F.sub.c and F.sub.h) and measures the magnitudes of the corresponding control voltages (V.sub.1, V.sub.c and V.sub.h). Next, the VCO is swept at a nominal clock frequency to determine the times (T.sub.1, T.sub.2 and T.sub.h) that the control voltages (V.sub.1, V.sub.c and V.sub.h) occur during the sweep cycle. The control voltage of the VCO is then swept at a first and then a second rate during a sweep cycle to assure that the center frequency (F.sub.c) of the VCO occurs at the time (T.sub.c) midpoint of the sweep cycle. As a result, each VCO frequency can be determined by MPU monitoring according to the time that the VCO frequency occurs during the sweep cycle. This circuitry is useful in spectrum analyzers for indirectly determining the otherwise unknown frequency of a received signal.

Abstract: An additional mixer is included in the feedback loop of a PLL which can be one of the local oscillators of a dual conversion system. A fine tuning frequency synthesizer is coupled to an input of the additional mixer for providing fine frequency control of the PLL. The fine tuning frequency synthesizer can include an additional phase locked loop. Also, a feedback signal for suppressing noise created by another local oscillator can also be applied to the additional mixer.

Abstract: A temperature compensated power detector utilizes a temperature compensating diode connected to an inverting input of an amplifier to enable the amplifier to substantially cancel out undesirable temperature effects caused by a power level detector diode coupled to the non-inverting input of the amplifier. As a result, the amplifier output voltage tends to remain constant over temperature in response to a fixed power level being applied to the detector. A lookup table is utilized to determine the power level corresponding to a power detector output voltage of a particular magnitude.

Abstract: In a tracking filter, which includes a conventional phase locked loop having a phase detector, a filter and a voltage controlled oscillator adapted to track a wanted signal and attenuate unwanted signals and noise from an incoming spectrum of signals, there is provided a phase modulator and an additional filter adapted to attenuate further the unwanted signals and the noise without degrading the ability of the loop to track the wanted signal.