JP3101338B2 - Receive level display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception level display device capable of displaying a received electric field strength in order to set an antenna in a better direction, for example, in a satellite broadcast receiving system.

[0003]

2. Description of the Related Art In a receiver for receiving an FM modulation signal such as a satellite broadcast, a carrier-to-noise power ratio (hereinafter referred to as C / N) is proportional to a noise level in a demodulated output.
/ N indicates the quality of reception and can be displayed as a signal level. The noise of the FM demodulator has a property called triangular noise that becomes larger as the frequency increases. Therefore, the signal level can be displayed by detecting the high band of the demodulated output.

FIG. 2 is a configuration diagram showing a configuration of a conventional signal level display device. In this figure, a first IF signal output from an outdoor converter is input to a frequency down converter 11 via an input terminal 10. This frequency down converter 11 converts the first IF signal into a second IF signal having a lower frequency. This second IF signal passes through a band-pass filter (hereinafter referred to as BPF) 12,
The signal is input to an automatic gain control circuit (hereinafter referred to as AGC) 13, and the signal amplitude is controlled. The signal output from the AGC 13 is input to the FM demodulator 14 where the FM signal is demodulated.

[0005] In the conventional example, the FM signal is a BPF 15
Is supplied to the level detector 30 via the. Here, the pass frequency of the BPF 15 is set higher than the signal band of the baseband FM signal. The detection voltage from the level detector 30 is supplied to an analog / digital converter (hereinafter referred to as A / D) 17 and converted into a digital signal.

[0006] The CPU 31 performs arithmetic processing based on the level data from the A / D 17. The CPU 31 has an A / D
And a display circuit 2 for displaying display data obtained by the arithmetic processing.
5 are connected. Further, the CPU 31 is connected to a tuning circuit 27 that controls the tuning of the frequency downconverter 11. That is, the tuning circuit 27 outputs a control signal for automatically fine-tuning the frequency down-converter 11 based on tuning data, and the CPU 31 updates the display level at a predetermined timing in accordance with this operation.

The maximum value of the noise power is stored in the RAM 32. In this case, a non-channel is selected by the tuning circuit 27, and the level at this time is set as the maximum value of the noise power.
The CPU 31 stores the level data from the A / D 17 and the RAM 3
The C / N is detected by comparing the data stored in No. 2 with the data and performing arithmetic processing.

In such a device, the signal input to the frequency down-converter 11 is amplified to a constant amplitude by the AGC 13 and FM-demodulated. Here, when the cable for transmitting the first IF signal is disconnected, the carrier component is reduced and the noise component is almost completely eliminated. This signal is A
A good value may be obtained when C / N is detected after amplification to a constant amplitude by the GC 13. Therefore, there is a case where the display is far from the actual signal input level.

[0009]

SUMMARY OF THE INVENTION As described above, the first I
If the cable transmitting the F signal is disconnected, the carrier component becomes small and the noise component is almost completely absent. After amplifying this signal to a constant amplitude by the AGC 13,
When / N was detected, a good value was sometimes obtained. In this case, the display may be far from the actual signal input level.

An object of the present invention is to eliminate the above-mentioned problems and to provide a reception level display device which always displays an accurate reception level.

[Structure of the Invention]

[0012]

According to the present invention, there is provided a channel selection means for outputting a channel selection signal for channel selection of a designated channel, and a first intermediate frequency signal output from an outdoor converter as an input. Frequency conversion means for converting the station signal into a second intermediate frequency signal, first filter means for limiting the band of the second intermediate frequency signal, and constant amplitude of the signal passing through the first filter means Amplitude control means for controlling the signal to a value, demodulation means for demodulating a video signal on which an audio signal is superimposed from a signal passing through the amplitude control means, second filter means for extracting a noise component of the video signal, Detecting means for detecting C / N from the component, analog-to-digital converting means for converting the C / N detected by the detecting means into a digital signal, and extracting the audio signal component from the video signal. Filter means, a sound demodulation means for demodulating a PCM digital audio signal from a signal passed through the third filter means, a code signal generation means for generating a code signal from the PCM digital audio signal, and a MUSE In the case of a signal, a video conversion unit for converting a MUSE signal into a decoded Hi-Vision signal and an output of the demodulation unit or an output of the video conversion unit are input, and one of them is selected and output according to the state of the video signal. Selecting means, separating means for separating a synchronizing signal from a video signal output from the selecting means, and output signals of the analog / digital converting means, the code signal generating means and the separating means, and these signals Calculating means for calculating the reception level from the computer, and displaying the reception level calculated by the calculating means. Always accurate receiving level by and a display unit are displayed.

[0013]

The reception level is calculated based on the C / N of the demodulated signal, the asynchronous signal indicating that the audio signal is in an asynchronous state, and the video synchronization signal. Normally, the reception level is obtained from the C / N, but when the asynchronous signal is detected and the video synchronization signal is not detected, the reception level is set to “0” regardless of the C / N. Thus, an accurate reception level is always displayed.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of the present invention.

In FIG. 1, a first IF signal output from an outdoor converter is input to a frequency down converter 11 via an input terminal 10. This frequency down converter 11 converts the first IF signal into a second IF signal having a lower frequency. After passing through the BPF 12, the second IF signal is input to the AGC 13, where amplitude control for controlling the amplitude of the signal to a constant value is performed. The signal output from the AGC 13 is input to the FM demodulator 14 where the FM signal is demodulated.

The FM signal is input to the BPFs 15 and 18, the MUSE decoder 21 and the switch 22. Of these, the noise component of the FM signal input to the BPF 15 is detected and output to the C / N detector 16. C / N detector 16
Detects the C / N value from the input signal and supplies the detected value to the A / D 17. The A / D 17 converts the detected C / N value into a digital signal and outputs the digital signal to a microcomputer (hereinafter referred to as a microcomputer) 24.

The FM signal input to the BPF 18 detects an audio signal component and is output to the QPSK demodulator 19.
The QPSK demodulator 19 demodulates a digital audio signal from the input signal and outputs it to the PCM decoder 20. PC
The M decoder 20 performs frame synchronization detection, error correction, code conversion, and the like, and outputs a digital audio signal of a binary code to the microcomputer 24. In particular, if no frame synchronization is detected, an NSYNC signal is output.

When the received FM signal is a MUSE signal, the FM signal is decoded by the MUSE decoder 21 and the switch 22 selects an output signal of the MUSE decoder 21. On the other hand, in the case of a normal FM signal, the switch 22
The FM signal output from the demodulator 14 is selected and output to the sync separation circuit 23. The switch 22 is selected by the microcomputer 2
4. The synchronization separation circuit 23 separates a synchronization signal from the input signal and supplies the synchronization signal to the microcomputer 24.

The microcomputer 24 performs an arithmetic process for determining the reception level from the input C / N detection value and the presence or absence of the NSYNC signal and the synchronization signal. The microcomputer 24 is connected to a display circuit 25 for displaying display data obtained by the arithmetic processing. In addition, microcomputer 2
4 is connected to a tuning circuit 27 for controlling the tuning of the frequency downconverter 11. That is, the tuning circuit 27 outputs a control signal for performing the automatic fine tuning control of the frequency down-converter 11 based on the tuning data, and the microcomputer 24 updates the display level at a predetermined timing in accordance with this operation.

Normally, the microcomputer 24 calculates and displays the reception level based on the C / N detection value. Here, the reception level is displayed as "0" when the C / N detection value is the same as the noise level, or when the NSYNC signal is detected and the video synchronization signal is not detected. In the latter case, the reception level is displayed as "0" regardless of the C / N detection value. This can be determined as a case where the cable for transmitting the first IF signal is disconnected.

Here, whether the reception level is determined to be "0" when the NSYNC signal is detected and the video synchronization signal is not detected will be described. When a scrambled video signal is received, a video synchronization signal cannot be detected even if it is correctly received. However, the audio signal is received properly. Therefore, the NSYNC signal is not detected. In the case of receiving a high-definition broadcast via a MUSE decoder or the like, an NSYNC signal is detected at the same time when a video synchronization signal is detected. From these facts, when the NSYNC signal is detected and the video synchronization signal is not detected, the reception level is determined to be “0”,
indicate.

As described above, the C /
N and NSYN indicating that the audio signal is out of synchronization
The reception level is calculated by calculation based on the C signal and the video synchronization signal. Normally, the reception level is obtained from C / N.
When the YNC signal is detected and the video synchronization signal is not detected, the reception level is set to “0” regardless of C / N. As a result, an accurate input level can be displayed even when the transmission cable of the first IF signal is disconnected, during a high-definition broadcast, or during a scrambled broadcast.

[0023]

The C / N of the signal demodulated as described above
And NSYNC indicating that the audio signal is in an asynchronous state.
The reception level is obtained by calculation based on the signal and the video synchronization signal. Normally, the reception level is obtained from C / N.
When the NC signal is detected and the video synchronization signal is not detected, the reception level is determined to be "0" regardless of the C / N and displayed. Thereby, an accurate reception level can always be displayed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing the configuration of the present invention.

FIG. 2 is a configuration diagram showing a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Input terminal 11 ... Frequency down converter 12,15,18 ... BPF 13 ... AGC 14 ... FM demodulator 16 ... C / N detector 17 ... A / D 19 ... QPSK demodulator 20 ... PCM decoder 21 ... MUSE decoder 22 ... Switch 23 ... Sync separation circuit 24 ... Microcomputer 25 ... Display circuit 27 ... Tuning circuit

Continuation of the front page (56) References JP-A-61-274495 (JP, A) JP-A-3-86683 (JP, U) JP-A-2-128489 (JP, U) JP-A-2-16681 (JP, A) , U) Hikaru 1-177678 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 17/00 H04B 1/06

Claims (1)

(57) [Claims] 1. A channel selection means for outputting a channel selection signal for channel selection of a designated channel, and a first intermediate frequency signal output from an outdoor converter as an input, and a second channel selection signal based on the channel selection signal. Frequency conversion means for converting to an intermediate frequency signal, first filter means for limiting the band of the second intermediate frequency signal, and amplitude control means for controlling the amplitude of the signal passing through the first filter means to a constant value Demodulating means for demodulating a video signal on which an audio signal is superimposed from the signal passed through the amplitude control means, second filter means for extracting a noise component of the video signal, and detecting C / N from the noise component Detecting means for converting the C / N detected by the detecting means into a digital signal; a third filter means for extracting an audio signal component from the video signal; Audio demodulation means for demodulating a PCM digital audio signal from the signal passed through the third filter means, code signal generation means for generating a code signal from the PCM digital audio signal, and MUSE
In the case of a signal, a video conversion unit for converting a MUSE signal into a decoded Hi-Vision signal and an output of the demodulation unit or an output of the video conversion unit are input, and one of them is selected and output according to the state of the video signal. Selecting means, separating means for separating a synchronizing signal from a video signal output from the selecting means, and output signals of the analog / digital converting means, the code signal generating means and the separating means, and these signals 1. A reception level display device comprising: a calculation means for calculating a reception level from a computer; and a display means for displaying the reception level calculated by the calculation means.