Radio with broad band automatic gain control circuit

Claim 2

A radio in which a broad band automatic gain control of a radio frequency circuit is performed compris­ing: a first detecting means for detecting the inten­sity of the electric field of a received signal; a second detecting means for detecting whether or not said broad band-automatic gain control is operating; and a means for changing the tuning condition of a radio frequency tuning circuit in a small extent in response to the signals outputted from said first and second detect­ing means.

Claim 3

A radio comprises a radio frequency (RF) amplifier circuit for amplifying a signal received by an antenna, an RF tuning circuit for tuning an RF signal outputted from the RF amplifying circuit, a mixing circuit which mixes the RF signal with an oscillation signal outputted from a local oscillation circuit to generate an intermediate frequency (IF) signal, an IF amplifying circuit for amplifying the IF signal, IF tuning circuits for tuning the IF signal, an IF signal detecting circuit for detecting the IF signal, a phase-locked loop (PLL) for applying a tuning voltage to a varactor diode provided in the RF tuning circuit and the local oscillation circuit, a radio frequency automatic gain control (RFAGC) circuit for effecting a broad band AGC and an intermediate frequency automatic gain control (IF-AGC) circuit for performing an AGC operation in accordance with the level of a signal outputted from the detecting circuit, an antenna dumping circuit for performing a broad band AGC, a stop signal being generated while an automatic search operation is being performed through an electric field intensity-detecting circuit, a distinction circuit, and a control circuit, a first detecting circuit for detecting whether or not the intensity of the electric field of a received signal is more than a predetermined level, a second detecting circuit for detecting whether or not an RF-AGC circuit is operating, and a control circuit for generating a control signal for changing the tuning condition created by a PLL in a small extent when signals are simultaneously outputted from the first detecting circuit and the second detecting circuit.

Claim 4

A radio comprises a radio frequency (RF) amplifier circuit for amplifying a signal received by an antenna, an RF tuning circuit for tuning an RF signal outputted from the RF amplifying circuit, a mixing circuit which mixes the RF signal with an oscillation signal outputted from a local oscillation circuit to generate an intermediate frequency (IF) signal, an IF amplifying circuit for amplifying the IF signal, IF tuning circuits for tuning the IF signal, an IF signal detecting circuit for detecting the IF signal, a phase-locked loop (PLL) for applying a tuning voltage to a varactor diode provided in the RF tuning circuit and the local oscillation circuit, a radio frequency automatic gain control (RFAGC) circuit for effecting a broad band AGC and an intermediate frequency automatic gain control (IF-AGC) circuit for performing an AGC operation in accordance with the level of a signal outputted from the detecting circuit, an antenna dumping circuit for performing a broad band AGC, a stop signal being generated while an automatic search operation is being performed through an electric field intensity-detecting circuit, a distinction circuit, and a control circuit, a first detecting circuit for detecting whether or not the intensity of the electric field of a received signal is more than a predetermined level, a second detecting circuit for detecting whether or not an RF-AGC circuit is operating, and a control circuit for generating a control signal for changing the tuning condition created by a PLL in a small extent when signals are simultaneously outputted from the first detecting circuit and the second detecting circuit.

Claim 5

The radio as defined in Claim 1, wherein the tuning frequency of the RF tuning circuit is changed by changing the control voltage which is to be applied from the PLL to the varactor diode provided in the RF tuning circuit.