Receiving apparatus and C/N ratio indication method thereof

#The present invention relates to a receiving apparatus that receives a digital satellite broadcast and to a C/N ratio indication method of the receiving apparatus, the method being is used to adjust an antenna level or the like.

#A satellite broadcast tuner, a television receiver that has an internal satellite broadcast tuner, and so forth have an antenna level indication function that indicates the C/N (Carrier to Noise) ratio of a reception signal received from a satellite by an antenna. The antenna level indication function is used for example to adjust the direction of an antenna that is installed.

#In the satellite broadcast, a parabola antenna that has a sharp directivity is used to receive a signal from the satellite. Thus, after the antenna has been installed, the direction of the antenna should be adjusted.

#FIG. 1 is a block diagram showing an example of a satellite broadcast receiving apparatus according to the present invention.

#FIG. 2 is a block diagram describing an indication of an C/N ratio of the satellite broadcast receiving apparatus according to the present invention.

#FIG. 3 is a schematic diagram describing the arrangement of signal points on a complex plane of the QPSK modulation.

#Next, with reference to the accompanying drawings, an embodiment of the present invention will be described. FIG. 1 shows an example of a digital BS broadcast receiving apparatus according to the present invention. In FIG. 1, a radio wave of 12 GHz band of a digital satellite broadcast is transmitted from a satellite and received by a parabola antenna 1. An LNB (Low Noise Block Down Converter) 2 mounted on the parabola antenna 1 converts the radio wave into a first intermediate frequency signal of for example 1 GHz band. An output of the LNB 2 is supplied to a tuner circuit 4 through a cable 3.

#A tuning signal is supplied from a microprocessor 25 to the tuner circuit 4. The tuner circuit 4 selects a desired carrier frequency signal from the reception signal on the basis of the tuning signal supplied from the microprocessor 25. The tuner circuit 4 converts the selected carrier frequency signal into a second intermediate frequency signal.

#The intermediate frequency signal is supplied from the tuner circuit 4 to an AGC circuit 5. The AGC circuit 5 amplifies the intermediate frequency signal supplied from the tuner circuit 4. In addition, the AGC circuit 5 controls the gain of the intermediate frequency signal so that the signal level thereof becomes constant. An output of the AGC circuit 5 is supplied to a demodulation circuit 6.