JPH05300410A - Fm receiver - Google Patents

Abstract

PURPOSE:To use a compact antenna and to reduce reception cost by performing the signal processing pulse-shaped noise generated by a threshold phenomenon in the receiver so that no noise can appear at received pictures. CONSTITUTION:The part of an FM signal lowering the level of the envelop almost to zero is a part where small fish-shaped noise appears on the screen and when small fish-shaped noise (c) and (d) is detected at a scanning line N under scanning at present, signals outputted from a switcher 7 are changed over. Then, the signal of a scanning line N-1 1H delaying an FM signal is selectively outputted by a control signal pulse from a control signal generating circuit 4. Thus, the small fish-shaped noise caused by the threshold phenomenon is prevented from appearing on the screen. Since this noise is generated at random, the probability of generating the noise at the same position of the adjacent scanning lines is extremely low and since the video signals are strongly correlated between the adjacent scanning lines, the part of detecting the noise can be compensated by the video signals of the adjacent scanning lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver. The electric field of the received radio waves entering the receiver weakens,
When the influence of noise generated inside the receiver becomes large, impulse noise suddenly increases in the demodulation output of the receiver from a certain level of the input electric field, impairing the reception quality and making it impractical. The level is called the threshold level. In recent years, SHF using satellite
In broadcasting, a video signal is FM-modulated and transmitted, but a communication satellite (CS) has transmission power of a broadcasting satellite (B
Since it is smaller than S), a large antenna is required. In addition, since the radio waves from the satellites are attenuated by rainfall, even in good reception quality in fine weather, the radio waves may be attenuated and fall below the threshold level in rain, resulting in conspicuous noise on the reception screen. is there.

[0002]

2. Description of the Related Art Conventionally, therefore, a large antenna should be used in consideration of attenuation of radio waves during rainfall so that the electric field input to the receiver does not fall below a threshold level even during rainfall. I was doing

[0003]

If the antenna is enlarged, the installation place is limited and the reception cost becomes high. INDUSTRIAL APPLICABILITY The present invention prevents pulse-like noise generated by the threshold phenomenon from appearing on the reception screen by performing signal processing in the reception device, and enables the use of a small antenna, thereby reducing the reception cost. The purpose is to reduce.

[0004]

FIG. 1 is a block diagram of an electric circuit of an essential part of an FM receiver showing an embodiment of the present invention. As shown in FIG. 1, an FM signal input is applied to one horizontal scanning period. A delay circuit 5 for delaying and outputting, a switcher 7 for switching the signals by inputting the FM signal input and the output of the delay circuit 5, and an FM for FM demodulating and outputting the input from the switcher 7. The demodulator 8, the linear detector 2 that envelope-detects the FM signal input and outputs the demodulator 8, and controls by detecting the period when the envelope level of the FM signal detected by the linear detector 2 falls below a predetermined level. And a control signal generation circuit 4 for outputting a signal. The control signal from the control signal generation circuit 4 is input to the switching device 7, and normally, the FM signal input is output from the switching device 7 and the FM demodulator is output. 8 in FM
When demodulation is performed and the envelope of the FM signal input falls below a predetermined level, the output signal is switched, the input signal from the delay circuit 5 is output from the switch 7, and the FM demodulator 8 performs FM demodulation. It was done.

[0005]

FIG. 3 is an explanatory diagram of the envelope waveform of the FM wave high frequency signal. The FM wave has a flat envelope as shown in FIG. When noise is included due to the threshold phenomenon or the like, the magnitude of the amplitude of the envelope changes due to the influence of frequency components included in the noise, as shown in FIG. The portion where the envelope is close to the zero value is a portion where edgy noise appears on the reception screen. The linear wave detector 2 detects the high frequency signal of the FM wave with the envelope, and the control signal generation circuit 4 closes the envelope to the zero value. However, for example, in the diagram (B), by detecting the points a and b, outputting a control signal, and switching the switch 7 based on the control signal, the signal of the scanning line is switched, and the scanning line is switched. 1H (H represents the period of the horizontal synchronizing signal)
The signal of the scanning line which does not include the noise of the previous meditation is output and is FM-demodulated by the FM demodulator 8. The pulse-shaped noise generated by the threshold phenomenon appears on the reception screen. You can avoid it.

[0006]

1 is a block diagram of an electric circuit of an essential part of an FM receiver showing an embodiment of the present invention. Reference numeral 1 denotes an input terminal to which an FM signal received by the receiving section of the FM receiving device is input. The FM signal input is branched to input the first directly to the switching device 7 and the second to the delay circuit. Enter 5 and the third
Is input to the linear detector 2. In the delay circuit 5, the FM
The signal input is output after being delayed for 1H period and input to the switching unit 7. The switching unit 7 switches between the FM signal input input through the input terminal 1 and the output of the delay circuit 5 and outputs the FM signal.
Input to the demodulator 8, and the FM demodulator 8 receives the input FM
Demodulates signal and outputs video signal and audio subcarrier signal 9
, And display it on the screen based on the same video signal.
An audio signal is reproduced based on the same audio subcarrier signal. The linear detector 2 detects the envelope of the input FM signal, outputs it, and inputs it to the control signal generation circuit 4.

FIG. 2 is an explanatory diagram of the output waveform of the linear detector 2 and the control signal waveform. As shown in FIG. 2, the linear detector 2 outputs the envelope of the FM signal, and the control signal is controlled. The signal generation circuit 4 detects a period in which the envelope level drops below a predetermined level (control set level). For example, in the case of FIG. 2, the periods T1 and T2 are detected and the periods T1 and T2 are detected. A corresponding control signal pulse is generated and the control signal pulse is input to the switch 7. Normally, the switch 7 outputs the FM signal input inputted through the input terminal 1, and when the control signal pulse is inputted from the control signal generation circuit 4, during the control signal pulse periods T1 and T2, The FM signal to be output is switched to output the FM signal delayed by 1H by the delay circuit 5, so that the video signal of the scanning line being currently scanned can be partially replaced and complemented.

FIG. 4 is an explanatory diagram of noise appearing on the screen due to the threshold phenomenon. As shown in FIG.
The portion where the level of the signal envelope has dropped to near zero is a portion where edgy noise appears on the screen, and when edgy noises c and d are detected on the scanning line N which is currently being scanned, the switching unit The signal output from 7 is switched so that the signal of the scanning line (N-1) obtained by delaying the FM signal by 1H is selected and output from the control signal generation circuit 4 by the control signal pulse. The noise that appears like a lump is prevented from appearing on the screen. Since the noises that are lumpy due to the threshold phenomenon occur randomly, the probability that they will occur at the same position on adjacent scanning lines is extremely low, and the video signal has a strong correlation between the adjacent scanning lines, and noise Even if the detected portion is complemented with the video signal of the adjacent scanning line, the image quality is not deteriorated.

[0009]

As described above, according to the present invention,
By performing signal processing in the receiving device, the noise like the noise due to the threshold phenomenon can be prevented from appearing on the screen, and the receiving antenna can be downsized and the receiving cost can be reduced. A device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of an essential part of an FM receiver showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an output waveform of a linear detector and a control signal waveform.

FIG. 3 is an explanatory diagram of an envelope waveform of an FM wave.

FIG. 4 is an explanatory diagram of noise that appears on a screen due to a threshold phenomenon.

[Explanation of symbols]

 1 Input Terminal 2 Linear Detector 4 Control Signal Generation Circuit 5 Delay Circuit 7 Switcher 8 FM Demodulator 9 Output Terminal

Claims (1)

[Claims] 1. A delay circuit that delays and outputs an FM signal input for one horizontal scanning period, a switcher that inputs the FM signal input and the output of the delay circuit, and switches and outputs the signals, and the same switcher. FM demodulator for FM demodulating and outputting the input from, the linear detector for envelope detecting the FM signal input and outputting, and the level of the envelope of the FM signal detected by the linear detector is below a predetermined level. And a control signal generating circuit for detecting a lowered period and outputting a control signal. The control signal from the control signal generating circuit is input to the switch, and normally, the FM signal input is input from the switch. When the output signal is output and FM demodulated by the FM demodulator, and the envelope of the FM signal input drops below a predetermined level, the output signal is switched and the input signal from the delay circuit is switched from the switcher. An FM receiving apparatus which outputs and FM demodulates with the FM demodulator.