Abstract: An RF modulator/switch selectably couples a locally generated and conducted RF signal or an antenna RF signal to a broadcast radio receiver. A local RF input receives the conducted RF signal. An antenna RF input receives the antenna RF signal in response to a radiated RF broadcast in a broadcast band. A resonant network has a first node coupled to the antenna RF input and has a resonant frequency corresponding to the broadcast band. A first relay has a first output selectably coupled to either the antenna RF input or a second node of the resonant network. A second relay has a second output selectably coupled to either the local RF input or the first output of the first relay. When the second relay selects the local RF input then the first relay selects the second node of the resonant network and when the second relay selects the first output of the first relay then the first relay selects the antenna RF input.

Abstract: An RF modulator/switch selectably couples a locally generated and conducted RF signal or an antenna RF signal to a broadcast radio receiver. A local RF input receives the conducted RF signal. An antenna RF input receives the antenna RF signal in response to a radiated RF broadcast in a broadcast band. A resonant network has a first node coupled to the antenna RF input and has a resonant frequency corresponding to the broadcast band. A first relay has a first output selectably coupled to either the antenna RF input or a second node of the resonant network. A second relay has a second output selectably coupled to either the local RF input or the first output of the first relay. When the second relay selects the local RF input then the first relay selects the second node of the resonant network and when the second relay selects the first output of the first relay then the first relay selects the antenna RF input.

Abstract: An improved tuner for a varactor-tuned local oscillator in a radio receiver includes a winding of a pair of magnetically coupled inductors, preferably constructed in the form of a transformer. Preferably, the first and second windings are magnetically coupled with reduced inter-winding capacitance by axially separating the windings on a common core. The second winding is selectively coupled by a switch to a capacitive load in order to change the inductance of the first winding. The tuning range of the resonant circuit formed by the varactor diode set and the first winding is changed when the capacitive load is coupled. The magnetic coupling between the transformer windings provides DC isolation between the oscillator and the switching circuit. Preferably, a tuning actuator has overlapping ranges of movement for selection of a signal within both the AM and FM frequency bands as the intermediate frequencies for the local oscillator are generated.