JPH055231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television antenna switching device that is effective for use in a vehicle-mounted television antenna mounted on a moving object such as an automobile.

BACKGROUND TECHNOLOGY AND PROBLEMS Traditionally, as a reception method for in-vehicle television, multiple antennas, each with different directivity, are switched.
Methods for selecting antennas with good radio wave conditions,
A variety of diversity reception methods, such as a method of switching the directivity of one antenna, are used. As a system using a plurality of antennas, an antenna switching device shown in FIG. 1 is conventionally known.

In Fig. 1, four antennas 1, 2, 3,
4 are the directivity shown in Fig. 2, respectively.
have. These antennas 1, 2, 3, 4
The television signal received by the switching circuit 5
Accordingly, the predetermined H in the vertical blanking period
Sequential sampling is performed for each antenna during a period (H: horizontal scanning period). This sampling is performed by the switching signal _S1 applied from the control circuit 11 at the timing shown in FIG. This switching circuit 5 selects one of the signals received by the antennas 1 to 4 during periods other than the H period during which sampling is performed. The signal obtained from the switching circuit 5 is tuned by a tuner 6, converted to an intermediate frequency signal, and further detected by a detection circuit 7. This detection output is supplied to the receiving circuit 8, as well as to the synchronization separation circuit 9 and the maximum level antenna detection circuit 10. The detection circuit 10 detects, during the predetermined H period, detection outputs corresponding to the received signals of the antennas 1 to 4 sequentially obtained by the sampling, based on the synchronization signal applied from the synchronization separation circuit 9. At the same time, the antenna from which the maximum level is obtained among the levels of each detected detection output is detected. This detection is performed by comparing the pedestal levels sampled during the H period. Based on this detection, the control circuit 11 applies a switching signal S ₁ to the switching circuit 5 to select the antenna that provides the maximum level of detected output. As a result, the switching circuit 5 selects the antenna from which the maximum level can be obtained until the next sampling is performed. When the next predetermined H period begins, the control circuit 11 forms a switching signal S ₁ for sampling again based on the synchronizing signal and applies it to the switching circuit 5 . Note that the above sampling is normally performed for each even field or odd field.

According to the above, in the video period of the received signal,
Since the antenna with the strongest field strength is always selected, it is possible to always receive good reception. Furthermore, since the above-mentioned sampling is performed during the vertical blanking period, the influence of sampling does not appear on the screen. However, in the case of audio signals,
During the amplification period, low-level signals sampled from antennas with weak electric field strength are momentarily mixed in, and this appears as buzz noise, which can be extremely difficult to hear. be.

OBJECTS OF THE INVENTION The present invention provides an antenna switching device for selecting the directivity direction of an antenna used in a vehicle-mounted television or the like, which reduces noise in audio signals.

Summary of the Invention The switching circuit for the television antennas 1 to 4 according to the present invention sequentially samples received signals from a plurality of directional directions of the television antenna during a vertical blanking period, thereby selecting the directional direction in which the maximum input level can be obtained. Based on this detection, the pointing direction in which the maximum input level can be obtained is selected during the period until the next sampling is performed, and the received signal from the pointing direction in which the maximum input level can be obtained reaches a predetermined level or higher. In some cases, the switching device of the television antennas 1 to 4 that stops the sampling integrates the vertical synchronization signal VD when the received signal from the directional direction where the maximum input level is obtained is at or above the predetermined level. Integrating means 18
, first and second sample and hold means 19 and 20 that sample desired portions of the output of the integration means 18, respectively, and addition means 2 to which the outputs of these sample and hold means 19 and 20 are input.
1, and a comparison means 22 to which the output of the addition means 21 and the reference signal V _P are input. This makes it possible to reduce the aforementioned audio noise in this type of antenna switching device.

Embodiment FIG. 4 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 1 are given the same reference numerals. still,
It is assumed that the four antennas 1 to 4 each have the directivity shown in FIG. 2 as in the case of FIG. 1.

In FIG. 4, the detection output of the detection circuit 7 is applied to an amplification circuit 10, a synchronous separation circuit 9, a determination circuit 14, and also to a sample hold circuit 12. The power of the amplifier circuit 10 is applied to the cathode ray tube 16. The sample hold circuit 12 includes switches _SW1 to _SW4 , _SW11 to _SW14 , and diodes D1 to _SW14 .
It is constructed as shown in the figure by _D4 , capacitors _C1 to _C4, etc. The switches SW ₁ to SW ₄ correspond to the antennas 1 to 4, respectively, and are switched in synchronization with the switching operation of the switching circuit 5 by a switching signal S ₁ from the control circuit 11. As a result, the detection output is sampled at the timing shown in FIG. The level of each sampled detection output is held in capacitors _C1 to _C4 through diodes _D1 to _D4 , respectively. Switch SW ₁₁ ~
SW ₁₄ is closed for a predetermined period of time by a switching signal S ₂ from control circuit 11 just before the next sampling to discharge capacitors C ₁ -C ₄ .

Capacitor C ₁ ~ corresponds to antennas 1 ~ 4
The detected output levels held at _C4 are applied to the maximum level antenna detection circuit 13.
This detection circuit 13 detects the antenna with the maximum input level and outputs a detection signal Sa indicating the antenna. This detection signal Sa is latched by a latch circuit 15. The determination circuit 14 determines whether the video signal received by the maximum input level antenna obtained from the detection circuit 7 is at a predetermined level or higher, and applies the determination signal S ₃ to the control circuit 11 . In order to make this determination, the determination circuit 14 detects, for example, the level of the synchronization pulse during the vertical blanking period. Note that an embodiment of this determination circuit 14 will be described later.

In the above configuration, it is assumed that the antenna with the maximum input level is the antenna 1 having the directivity shown in FIG. A detection signal Sa indicating the antenna 1 obtained from the latch circuit 15 is applied to the control circuit 11. The control circuit 11 responds to the detection signal Sa,
After the sampling is completed, a switching signal _S1 for selecting antenna 1 is applied to switching circuit 5.

During the period when the switching circuit 5 selects the antenna 1, the determination circuit 14 determines whether the video signal is at a predetermined level or higher that is large enough to obtain a screen that does not cause any problems in practical use. When the video signal is at a predetermined level or higher, a determination signal _S3 indicating this is applied to the control circuit 11. In response to this, control circuit 1
1 is applied to the switching circuit 5 and the sample and hold circuit 12 to stop the next sampling and to maintain the selection of the antenna ₁ . In this way, antenna 1 is continuously selected during the period when the video signal is at a predetermined level or higher. When the video signal falls below a predetermined level, a judgment signal S ₃ is sent to indicate this.
is sent to the control circuit 11. In response to this, the control circuit 11 cancels the suspension of sampling and outputs a switching signal _S1 for sampling all antennas 1 to 4 again in the next sampling period.

As described above, in this embodiment, once the video signal obtained from the selected antenna is maintained at a predetermined level, it is fixed to that antenna and sampling is not performed, so noise may be mixed into the audio. There are fewer opportunities to do so. In addition, in the conventional method, sampling is performed periodically, so audio interruptions caused by low-level signals can be heard as continuous bass sounds, but according to this embodiment, sampling is performed irregularly. The breaks in the sound are discontinuous, which greatly reduces buzzing noise. Also, while the antenna is fixed, the antenna with the maximum input level may change to another antenna, but during the period when the antenna is fixed, the video signal maintains at least a predetermined level or higher, so the screen is There is no disturbance and a practically good screen can be obtained.

Next, the determination circuit 14 of this embodiment is shown in FIGS.
The diagram will be explained.

In FIG. 5, the vertical synchronization signal VD and other synchronization pulses shown in FIG.
The voltage VS will have the integral waveform shown in the figure. This voltage VS is applied to sample-and-hold paths 19 and 20, and sampled by sampling pulses P ₁ and P ₂ applied at predetermined timings from the control circuit 11 in FIG. 4. A voltage V ₁ corresponding to the level of the vertical synchronizing signal VD is obtained from the sample and hold circuit 19, and a voltage V ₂ corresponding to approximately the pedestal level is obtained from the sample and hold circuit 20. These voltages V ₁ and V ₂ are applied to an adder 21 to perform a subtraction of V ₁ −V ₂ =ΔV, and the difference voltage ΔV is compared with a reference voltage Vp in a comparison circuit 22. Then, the comparison circuit 22 outputs a judgment signal S 3 indicating that the video signal is above a predetermined level when ΔV≧Vp, and outputs a judgment signal S ₃ indicating that the video signal is lower than the predetermined level when ΔV<Vp _. Output.

FIG. 7 shows a reference example of the determination circuit 14.
This reference example shows the AGC voltage obtained from the AGC circuit 24.
It uses Vc.

The AGC circuit 24 responds to the output of the detection circuit 7.
The AGC voltage Vc is obtained, and the gain of the intermediate frequency amplification circuit of the tuner 6 is controlled by this voltage Vc. In this reference example, the AGC voltage Vc is detected by the level detection circuit 25.
In addition to detecting the level V ₃ for a predetermined period, this V ₃
The comparison circuit 26 compares the voltage with the reference voltage Vp to obtain the determination signal _S3 .

The embodiments and reference examples of the present invention described above are described in the second section.
As shown in the figure, the antenna with the maximum input level is selected by switching between four antennas 1 to 4, each with a different directivity, but the present invention changes the directivity of one antenna as shown in Figure 2. It can also be applied to the case where the directivity that provides the maximum input level is selected by sequentially switching. Therefore, the present invention can generally be applied to the case where a plurality of directivity directions for one or more television antennas are switched to select the directivity direction that provides the maximum input level.

Effects of the Invention Since sampling is stopped when the received signal from the direction in which the maximum input level is obtained is above a predetermined level, audio noise can be reduced.

Furthermore, since the sampling is performed irregularly, the interruption of the sound is discontinuous, so that the buzz sound can be greatly reduced.

Further, since the video signal maintains at least a predetermined level during the period when the sampling link is stopped, the screen is not disturbed and a practically good screen can be obtained.

Further, it is determined that the received signal from the pointing direction where the maximum input level is obtained is at a predetermined level or higher, and the integration means for integrating the vertical synchronization signal and the first and second input signals for sampling desired points of the output of the integration means, respectively. This is because the judgment is made by a judgment circuit comprising two sample and hold means, an addition means to which the outputs of these sample and hold means are input, and a comparison means to which the outputs of the addition means and the reference signal are input. The determination level does not vary depending on the content of the video signal, making it possible to make very stable determinations. Therefore, the above-mentioned effects can be further enhanced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a diagram showing antenna directivity, and FIG. 3 is a timing chart showing the principle of antenna switching operation.
FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 6 is a block diagram showing an embodiment of the determination circuit, FIG. 6 is a timing chart of FIG. 5, and FIG. 7 is a block diagram showing a reference example of the stabilizing circuit. In addition, in the symbols used in the drawings, 1, 2,
3, 4...Antenna, 5...Switching circuit, 11...
...Control circuit, 12...Sample hold circuit, 1
3... Maximum level antenna detection circuit, 14... Judgment circuit.

Claims (1)

[Claims] 1. By sequentially sampling received signals from a plurality of directional directions of a television antenna during a vertical blanking period, the directional direction in which the maximum input level is obtained is detected, and based on this detection, the following A television that selects the directional direction in which the maximum input level can be obtained during the period until sampling is performed, and stops the sampling when the received signal from the directional direction in which the maximum input level can be obtained is at a predetermined level or higher. In the antenna switching device, the received signal from the directional direction where the maximum input level can be obtained is at or above the predetermined level.
an integrating means for integrating a vertical synchronization signal; first and second sample-hold means for sampling desired portions of the output of the integrating means; addition means to which the outputs of these sample-hold means are input; and said addition means. 1. A switching circuit for a television antenna, characterized in that the switching circuit for a television antenna is characterized in that the determination is made by a determination circuit comprising comparison means to which the output of the antenna and a reference signal are input.