Abstract: A technique for the automatic alignment and tuning of the front end of a vehicle radio. A tuning voltage is applied to a multiplying digital-to-analog converter before being applied to a front end tuning circuitry of the radio. A tuning voltage antenna number is applied to the tuning voltage at the converter to scale the tuning voltage, and adjust the center frequency tuning of the front end. During alignment, the tuning voltage antenna number is used to modulate the tuning voltage around a mean by reprogramming the tuning voltage antenna number a few values higher and lower in sequence. This modulation of the antenna tuning voltage creates an AC modulation component on the signal strength indicator signal passing through the front end. The signal strength indicator signal is measured and compared to its value before the tuning voltage antenna number was changed.

Abstract: A technique for reducing FM intrusion in an AM section of an AM/FM receiver. In one embodiment, a first switch is provided between an FM tuner filter circuit and an AM tuner circuit. A second switch is provided between the FM tuner circuit and a reference potential. When the receiver is in an FM mode, the first switch is closed so that a tuning voltage can be applied to the FM tuner circuit, and the second switch is open to prevent the tuning voltage from being affected by the reference potential. When the receiver is switched to the AM mode, the first switch is open to prevent intermodulation product signals generated by the FM tuner circuit from reaching the AM tuner circuit, and the second switch is closed to connect the FM tuner circuit to the reference potential. By connecting the FM tuner circuit to the reference potential when the receiver is in the AM mode, the tuning of the FM tuner circuit is shifted out of the FM bandwidth, thus eliminating intermodulation products at the AM frequencies.

Abstract: A method and apparatus for suppressing noise in a radio receiver or the like due to electromagnetic interference generated by the firing of a spark plug which coordinates the operation of a noise blanker with the EST signal generated by an electronic engine control module or similar spark timing signal. The apparatus of the present invention comprises a noise blanker disposed within a radio receiver for blanking the output of the radio receiver for a predetermined duration after a predetermined time delay has elapsed after each EST signal pulse. The noise blanker is activated for a time duration slightly longer than the duration of the impulse noise. The noise blanker may also be designed to be deactivated when the desired signal level reaches a predetermined level. The apparatus of the present invention may be used in conjunction with other noise suppression systems to eliminate noise due to sources other than the electronic ignition system.