JPS641809Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vehicle television reception antenna device that is mounted on and used in a vehicle such as an automobile.

[Conventional technology]

Conventionally, in order to eliminate the fading phenomenon caused by interference between direct waves from broadcast stations and reflected waves from buildings and road surfaces, TV reception was performed using multiple TV reception antennas installed on the vehicle via an antenna switching circuit. A vehicle television reception antenna device has been proposed in which a control circuit connects the antenna with the highest reception level to the antenna input circuit of the television receiver (Japanese Patent Laid-Open No. 56-10780). issue).

[The problem that the idea attempts to solve]

However, in the case of such a conventional vehicle television reception antenna device, the detection output level of each antenna is compared every time the television signal is vertically blanked, and the antenna with the highest output level is selected. The problem was that it required the same number of comparators and logic circuits as the number of antenna bases, making the circuit configuration complicated.

The present invention was developed based on the above-mentioned problems, and its purpose is to provide television reception with a simple circuit configuration that does not require the same number of comparators and logic circuits as the number of antenna bases. It is an object of the present invention to provide a television receiving antenna device for a vehicle that can be switched to an antenna.

[Means to solve the problem]

In order to solve the above problems, the present invention has a plurality of television reception antennas installed in a vehicle, and selectively transmits one of the detected outputs from each of these antennas to a television receiver installed in the vehicle. An input antenna switching circuit, a detection means for detecting the detection output level of the antenna input to the television receiver via the antenna switching circuit, and a detection means for detecting the detection output level detected by the detection means at a preset threshold. A comparator that outputs a signal when the detected output level is smaller than a threshold value, and a delay that delays the horizontal synchronization signal obtained from the detected output of the antenna input to the television receiver by 1/2 period and outputs it. The horizontal synchronization signal and vertical synchronization signal obtained from the detected output of the antenna input to the television receiver are input to the circuit, and based on these signals, a gate pulse whose pulse width corresponds to the antenna base times the horizontal synchronization signal is generated. a first gate pulse generating circuit that generates a gate pulse, and a second gate pulse generating circuit that outputs a horizontal synchronizing signal from the delay circuit as a gate pulse when the gate pulse from the first gate pulse generating circuit is at H level. and a switching clock generation circuit which receives the gate pulse from the second gate pulse generation circuit and outputs the output signal from the comparator as a switching clock; The antenna switching circuit is characterized in that it includes a shift register that sends a switching signal to the antenna switching circuit.

[Effect]

In this invention, the detection output level of the antenna input to the television receiver via the antenna switching circuit is compared with a preset threshold value using a comparator, and if the detection output level is smaller than the threshold value, the antenna is switched on. Since the antenna is switched, it is not necessary to have the same number of comparators and logic circuits as the number of bases of antennas, and it is possible to switch to a TV reception antenna with a good reception condition with a simple circuit configuration.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a vehicle television receiving antenna device showing an embodiment of the present invention. In the same figure, 1
- 4 are TV receiving antennas installed on the roof of the vehicle, etc. at a distance of 1/4 wavelength or more from each other, and these TV receiving antennas 1 to 4 are respectively feeder wires.
It is connected to the antenna switching circuit 5 via 11-14. This antenna switching circuit 5 is connected to each antenna 1 to
This is for selectively inputting one of the detection outputs from 4 to the television receiver 7 mounted on the vehicle, and the antenna input to the television receiver 7 is controlled by a switching signal from the shift register 17, which will be described later. configured to switch.

The television receiver 7 includes a tuner 71 that converts the detection output of the antenna input from the antenna switching circuit 5 via the high frequency amplifier 6 into two intermediate frequency signals of audio and video, and a video intermediate frequency signal from the tuner 71. intermediate frequency amplifier 72 that amplifies
A video detection circuit 73 amplitude-modulates the video intermediate frequency signal amplified by the intermediate frequency amplifier 72 to extract a video signal (television signal), and a video detection circuit 73 that processes the video signal from the video detection circuit 73 and outputs it to a cathode ray tube. 75, and a sync separation circuit (not shown) that separates and extracts a horizontal sync signal and a vertical sync signal included in the video signal from the video detection circuit 73. The extracted horizontal synchronizing signal is output from the horizontal drive circuit 76 as a horizontal drive pulse HP, and the vertical synchronization signal is output from the vertical drive circuit 77 as a vertical drive pulse VP.

Further, reference numeral 9 indicates a horizontal drive pulse supplied from the horizontal drive circuit 76 via the horizontal pulse shaping circuit 8.
HP is a delay circuit that delays the horizontal synchronization signal by 1/2 period and outputs it; 10 is the peak of the horizontal synchronization signal included in the video signal (television signal) TS supplied from the video detection circuit 73 of the television receiver 7; This is a peak value detection circuit that detects the value. The peak value of the horizontal synchronizing signal detected by the peak value detection circuit 10 is held in the peak hold circuit 11, and is compared with the threshold value from the threshold setting circuit 12 in the comparator 13. ing.

Further, 14 is a horizontal drive circuit 7 of the television receiver 7.
Horizontal drive pulse HP from 6 and vertical drive circuit 77
Based on the vertical drive pulse VP from
A first gate pulse generation circuit 15 generates a gate pulse VGP corresponding to 1.times.), and 15 generates a horizontal synchronization signal from the delay circuit 9 as a gate pulse when the gate pulse VGP from the first gate pulse generation circuit 14 is at H level. The gate pulse HGP output from the second gate pulse generating circuit 15 is supplied to the switching clock generating circuit 16.

The switching clock generation circuit 16 receives the gate pulse HGP from the second gate pulse generation circuit 15 and outputs the output signal from the comparator 13 as the switching clock CC. The switching clock CC is supplied to the shift register 17. This shift register 17 is configured to shift the register one by one each time the switching clock CC is input from the switching clock generating circuit 16, and to send a switching signal to the antenna switching circuit 5. In the figure, 18 is a malfunction detection circuit for detecting malfunction of the shift register 17, and 19 is an initial setting circuit for presetting the shift register 17.

Next, the operation of this embodiment configured as described above will be explained with reference to the waveform diagram shown in FIG.

First, when the power switch of the television receiver 7 is turned on, the initial setting circuit 19 is activated and the shift register 17 is preset. shift register 17
Preset. When the shift register 17 is preset, the antenna switching circuit 5 inputs the detected output of the antenna 1 to the television receiver 7 via the high frequency amplifier 6. The detected output of the antenna 1 input to the television receiver 7 is converted into two intermediate frequency signals of video and audio by a tuner 71, and then amplified by an intermediate frequency amplifier 72. The video intermediate frequency signal amplified by the intermediate frequency amplifier 72 is amplitude-modulated by the video detection circuit 73 and output as a video signal (television signal) TS. Video detection circuit 73
The video signal TS output from the video processing circuit 74
The signal is input to the peak value detection circuit 10, where the peak value of the horizontal synchronizing signal is detected. Then, the peak value of the horizontal synchronizing signal detected by the peak value detection circuit 10 is held in the peak hold circuit 11 and inputted to the comparator 13, where it is compared with the threshold value from the threshold setting circuit 12. be done. At this time, if the peak value of the horizontal synchronization signal is smaller than the threshold value, comparator 1
A signal is output from 3, and the switching clock generation circuit 1
6 is input.

On the other hand, when the horizontal drive pulse HP and the vertical drive pulse VP are input to the first gate pulse generation circuit 14, the gate pulse VGP whose pulse width corresponds to the antenna radix times the horizontal synchronization signal is output to the first gate pulse generation circuit 14. It is output from 14. Gate pulse output from the first gate pulse generation circuit 14
VGP is input to the second gate pulse generation circuit 15, and in the second gate pulse generation circuit 15, the first
The gate pulse from the gate pulse generation circuit 14 of
When VGP is at H level, the horizontal synchronizing signal from delay circuit 9 is output to switching clock generating circuit 16 as gate pulse HGP. The switching clock generating circuit 16 receives the gate pulse HGP from the second gate pulse generating circuit 15 and outputs the output signal from the comparator 13 to the shift register 17 as the switching clock CC. As a result, the shift register 17 shifts the register by one each time the switching clock CC is input from the switching clock generation circuit 16, and sends a switching signal to the antenna switching circuit 5 to change the antenna connected to the television receiver 7 from 1 to 1. Switch to 2. If the peak value of the horizontal synchronization signal obtained from the detection output of antenna 2 is larger than the threshold value, that state is maintained; if it is smaller than the threshold value, antenna 2 is switched to antenna 3, and the above-mentioned process is performed. The operation is repeated within the vertical retrace interval T.

In this way, in this embodiment, the peak value of the horizontal synchronization signal is compared with a threshold value set in advance by the comparator 13, and when the peak value is smaller than the threshold value, the antenna is switched. It does not require the same number of comparators and logic circuits as the number of radixes, and it is possible to switch to a TV reception antenna with a good reception condition with a simple circuit configuration.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the peak value of the horizontal synchronization signal is compared with the threshold value, but the difference between the peak value of the horizontal synchronization signal and the black level may be compared with the threshold value. . Alternatively, the color signal formed on the back porch of the horizontal synchronization signal may be compared with a threshold value.In short, the detection output level of the antenna is compared with a preset threshold value, and the detection output level is The antenna may be switched when the value is smaller than a threshold value.

[Effect of idea]

As explained above, the present invention compares the detected output level of the antenna input to the television receiver with a preset threshold value using a comparator, and switches the antenna when the output level is lower than the threshold value. As a result, it is possible to provide a television receiving antenna device for a vehicle that can switch to a television receiving antenna with a good reception condition with a simple circuit configuration without requiring the same number of comparators and logic circuits as the number of bases of antennas.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a vehicle television receiving antenna device showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment. 1-4...Television receiving antenna, 5...Antenna switching circuit, 7...Television receiver, 10...Peak value detection circuit, 12...Threshold value setting circuit, 13
... Comparator, 14, 15 ... Gate pulse generation circuit, 16 ... Switching clock generation circuit, 17
...Shift register.

Claims (1)

[Scope of utility model registration request] A plurality of television reception antennas installed on a vehicle, an antenna switching circuit that selectively inputs one of the detected outputs from each of these antennas to a television receiver installed on the vehicle, and this antenna switching circuit. a detection means for detecting the detection output level of the antenna inputted to the television receiver through the detection means; and a detection means for comparing the detection output level detected by the detection means with a preset threshold value, and determining whether the detection output level is the threshold value. a comparator that outputs a signal when the signal is smaller, a delay circuit that delays and outputs a horizontal synchronizing signal obtained from the detection output of the antenna input to the television receiver by 1/2 period, and a first gate pulse generation circuit that inputs a horizontal synchronization signal and a vertical synchronization signal obtained from the detection output of the antenna and generates a gate pulse having a pulse width corresponding to the antenna radix times the horizontal synchronization signal based on these signals; , a second gate pulse generating circuit that outputs the horizontal synchronizing signal from the delay circuit as a gate pulse when the gate pulse from the first gate pulse generating circuit is at H level; a switching clock generation circuit that receives a gate pulse from the comparator and outputs the output signal from the comparator as a switching clock; and a shift register that sends a switching signal to the antenna switching circuit each time a switching clock is input from the switching clock generation circuit. A television receiving antenna device for a vehicle, characterized by comprising: