Radio receiver

A receiver that receives a desired signal including a transmission signal and a supervisory signal, comprising:

• a calculating circuit including
• a first filter which passes the supervisory signal from the received desired signal,
• a second filter which passes noise accompanying the received desired signal,
• a first calculator which calculates a level of the supervisory signal being transmitted through the first filter,
• a second calculator which calculates a level of the noise output from the second filter, and
• a subtractor which calculates a difference between the level of the supervisory signal and the level of the noise;
• and
• a controlling circuit that controls outputting of the transmission signal from the receiver according to the difference, with the controlling circuit including
• a gain generator which generates a gain according to the difference;
• and
• a multiplier which amplifies the transmission signal according to the gain.

A portable telephone which receives a voice signal modulated by angle modulation and a supervisory signal for supervising the condition of the propagation path through which the voice signal is transmitted, and controls outputting of the voice signal according to the supervisory signal, the portable telephone comprising:

• a receiving circuit which receives a radio wave including the voice signal and the supervisory signal;
• a first filter which passes the supervisory signal;
• a second filter which passes noise whose frequency is different from the frequency band of the voice signal and the frequency of the supervisory signal;
• a first level calculator which calculates a level of the supervisory signal passing through the first filter;
• a second level calculator which calculates a level of the noise passing through the second filter;
• a subtractor which calculates a difference between the level of the supervisory signal and the level of the noise;
• a comparator which compares the difference with a threshold defined by the angle modulation;
• and
• a controller which controls outputting of the voice signal according to the result of the comparison obtained by the comparator.

A method for use of a radio receiver which receives a transmission signal and a supervisory signal for supervising a condition of a propagation path through which the transmission signal is transmitted, and controls outputting of the transmission signal according to the supervisory signal, the method comprising the steps of:

• detecting a level of the supervisory signal;
• detecting a level of noise whose frequency is different from the frequency band of the transmission signal and the frequency of the supervisory signal;
• calculating a difference between the level of the supervisory signal and the level of the noise;
• and
• controlling the outputting of the transmission signal according to the difference.