JPH06165059A - Automatic antenna switching device for automobile - Google Patents

Abstract

PURPOSE:To perform diversity reception which can prevent bar noise caused by antenna search from appearing in a picture even when a receiving state is adverse. CONSTITUTION:This automatic antenna switching device for performing the antenna search with a separated synchronizing signal as a reference by providing an antenna switching circuit 3 and a synchronizing signal separating circuit 8 for separating the synchronizing signal from the output video signal of a television receiver 4 is provided with a pseudo synchronizing signal generating means for generating a pseudo synchronizing signal when no synchronizing signal can be provided from the synchronizing signal separating circuit 8, and this pseudo synchronizing signal generating means utilizes the timer of a microcomputer built in a control circuit 2 and approximates the average cycle of the pseudo synchronizing signal to the cycle of the correct synchronizing signal by time sequentially combining generation enable cycles. When any synchronizing signal can not be provided from the synchronizing signal separating circuit 8 many times, the antenna search is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic antenna for selecting one antenna having the best reception condition from a plurality of antennas mounted on an automobile or combining a plurality of antennas and connecting them to a television receiver. Regarding the switching device, in particular,
Even when the reception condition is poor, the bar noise caused by the antenna search is prevented from appearing on the screen.

[0002]

2. Description of the Related Art In a television receiver mounted on an automobile, the receiving state changes remarkably as the vehicle travels. Therefore, a plurality of antennas should be provided on the automobile so that the antenna with the best receiving state can be selected. A diversity reception system has been conventionally known in which signals are combined and connected to a television receiver.

As shown in FIG. 3, a conventional antenna automatic switching apparatus for receiving diversity reception by a television receiver mounted on an automobile has a plurality of antennas 1a on a vehicle body.
1d are provided, and an antenna in a good reception state is connected to the television receiver 4 via an antenna switching circuit 3 controlled by the control circuit 2.

In order to control the switching operation of the switching circuit 3, a clamp circuit 5 to which a video signal output from the television receiver 4 is applied to fix the DC component of the video signal, and the clamp circuit 5. The output of the clamp circuit 5 and the sync signal separation circuit 8 for separating the sync signal from the video signal output from the antenna and guiding it to the control circuit 2 are provided for each antenna.
Sample and hold circuits 6a to 6d that sample and hold every 1a to 1d, and these sample and hold circuits 6a to 6d
A maximum level detection circuit 7 for transmitting sample / hold circuits 6a to 6d holding the highest reception level among the reception levels held in 6d to the control circuit 2 as detection signals.

As shown in FIGS. 4A and 4B, the control circuit 2 switches during the short period between the horizontal synchronizing pulses P ₁ and P ₂ existing in the vertical blanking period for each field or frame. The circuit 3 is controlled to switch the antennas 1a to 1d one by one and sequentially connect to the television receiver 4.

At this time, the waveform of the video signal output from the television receiver 4 and having the direct-current component fixed by the clamp circuit 5 is, as shown in FIG. 4B, connected antennas 1a to 1d. The signals of the crest values 11a to 11d whose reception levels fluctuate in accordance with the reception state are output, and the crest values 11a to 11d are respectively held in the sample and hold circuits 6a to 6d.

In the maximum level detection circuit 7, each of the peak values 11a to 11d held in the sample and hold circuits 6a to 6d.
The maximum reception level is detected from among the above, and the antenna having the highest reception level is selected based on the detected reception level and transmitted to the control circuit 2 as a detection signal.

In the control circuit 2, the antenna having a high reception level selected by this detection signal is continuously connected to the television receiver 4 until the next field or frame.

[0009]

In order to perform diversity reception, signals received by a plurality of antennas 1a to 1d are selected and supplied to a television receiver 4 via an automatic antenna switching device 3. In this case, even if synchronization cannot be continuously obtained due to a fading phenomenon, a pseudo synchronization signal is internally generated, and a timing such as an antenna search time is set based on the pseudo synchronization signal.

However, when the synchronization is lost several times or more in succession, the timing error of the pseudo sync signal is accumulated and increases, and the antenna search timing deviates from the vertical blanking period and the video signal There was a problem that the image was difficult to see due to white line-shaped bar noise appearing on the screen due to the antenna search.

Therefore, the present invention was conceived in order to prevent white line bar noise from appearing on the screen due to antenna search.

[0012]

According to the present invention, there is provided a vehicle antenna automatic switching device for performing diversity reception, wherein an antenna switching circuit for switching and connecting a plurality of antennas to a television receiver and an output from the television receiver. A synchronizing signal separating circuit for separating a synchronizing signal from a video signal, and an automatic antenna switching device for performing an antenna search based on the synchronizing signal separated by the synchronizing signal separating circuit. A pseudo sync signal generating means for generating a pseudo sync signal which serves as a reference for the timing of the antenna search is provided when the sync signal is no longer obtained. The pseudo sync signal generating means is built in the microcomputer. It uses a timer, and combines the cycles that can be generated in time series to generate a pseudo sync signal. To approximate the average period to the correct period of the synchronization signal.

When the sync signal cannot be obtained from the sync signal separation circuit many times, the antenna
Configure to stop the search.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the basic structure of an automatic antenna switching apparatus for performing diversity reception according to the present invention is almost the same as that of the conventional apparatus shown in FIG. , A synchronization signal detection circuit in the control circuit 2 for detecting the presence or absence of the synchronization signal separated by the synchronization signal separation circuit 8 using a microcomputer in the control circuit 2 and a timer built in the microcomputer. Prepare,
Further, a missing count counter 21 is provided for counting the number of times the vertical sync signal is missing.

Each time a vertical sync signal is detected, a timer is used to wait for the next vertical sync signal to arrive (16.68 m
sec)) and calculate a time (16.68msec + △ t)
If the vertical synchronizing signal is not detected even after the calculated time has elapsed, the missing counter 21 is incremented.
The missing count counter 21 is reset to 0 every time the vertical synchronization signal is detected. When the first vertical sync signal is not detected, the pseudo sync signal is generated with a period of time (16.68 msec + Δt).

If the pseudo sync signal is generated with a regular time (16.68 msec) as a cycle when the second and subsequent vertical sync signals are not detected, the timing error of the pseudo sync signal is not accumulated and the vertical sync signal is generated. If it detects a signal, it should be able to follow immediately.

However, since the pseudo sync signal is generated by the timer of the microcomputer, for example, 1
Even if it can be generated with a cycle such as 6.40, 16.60, 16.80, 17.00 msec, it is difficult to generate with a cycle of 16.68 msec.

Therefore, when the second and subsequent vertical synchronizing signals are not detected, the periods that can be generated by the timer of the microcomputer are combined in time series so that the average period becomes 16.68 msec which is almost the same as the vertical synchronizing signal. To generate a pseudo sync signal.

Even if the power of the television receiver 4 is turned on, when the reception condition of the antenna is poor, when a channel without broadcasting is selected, or when broadcasting is finished, the television receiver 4 The output video signal becomes an irregular noise signal, and a random signal is output from the sync signal separation circuit 8 due to this noise, and a sync signal cannot be obtained.

When the code for transmitting the video signal from the television receiver 4 is abnormal such as contact failure or disconnection, the output signal from the sync signal separation circuit 8 is at high level or low. The level is fixed, and the synchronization signal cannot be obtained.

As described above, when the vertical synchronizing signal is continuously lost many times (for example, 15 times), the power of the television receiver 4 is turned off or the cable for guiding the video signal is abnormal. It is determined that the antenna search is stopped, and white line bar noise is prevented from appearing on the screen.

The computer of the control circuit 2 is used to perform the operation shown in the flowchart of FIG.

Step 1: Examine the presence or absence of the vertical sync signal to determine whether the continuous loss of the vertical sync signal has occurred. Step 3a: If the first missing is detected, the first time Is set, the timing of the pseudo sync signal having a cycle corresponding to the omission is set, and the process proceeds to step 4, step 3b:
When the second missing is detected, the timing of the pseudo sync signal of the cycle corresponding to the second missing is set, and the process proceeds to step 4. Step 3b: When the third missing is detected, 3 The timing of the pseudo sync signal having a cycle corresponding to the loss of the first time is set, and the process proceeds to step 4. Step 4: The antenna search process is performed and the process returns to step 1.

Step 5: If it is determined in step 1 that there is a vertical synchronization signal, the missing counter is reset to 0 and the process proceeds to step 4.

Step 6: In Step 2, when N times (for example, 15 times) or more of omissions are detected, the antenna search is stopped and the process returns to Step 1.

Even if a sync signal is not obtained by performing such a series of operations, a pseudo sync signal having a cycle similar to the cycle of the sync signal can be generated. Therefore, the pseudo sync signal is used as a timing reference for the antenna. -When searching is performed, white bar noise does not appear on the screen. Moreover,
When the synchronization signal cannot be obtained many times, the antenna search is forcibly stopped, so that the white line bar noise does not appear on the screen.

[0027]

As is clear from the description based on the above embodiments, according to the automatic antenna switching apparatus for automobiles of the present invention which performs diversity reception, even if the reception condition is poor and the synchronization signal cannot be obtained, the synchronization signal can be obtained. Since the antenna search is performed using a pseudo sync signal with a cycle similar to the cycle as the timing reference, the timing of the antenna search deviates from the vertical blanking period and shifts to the period of the video signal. It is possible to avoid a situation in which white line-shaped bar noise appears and the image becomes difficult to see.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a vehicle antenna automatic switching device of the present invention,

FIG. 2 is a flow chart used to describe the operation of the device of the present invention,

FIG. 3 is a block diagram showing an example of a conventional automobile antenna automatic switching device;

FIG. 4 is a waveform diagram of a video signal used to describe the operation of the apparatus of the present invention and the conventional apparatus.

[Explanation of symbols]

 1a to 1d Antenna 2 Control circuit 21 Missing counter 3 Antenna switching circuit 4 Television receiver 5 Clamp circuit 6a to 6d Sample and hold circuit 7 Maximum level detection circuit 8 Sync signal separation circuit

Claims (2)

[Claims] 1. An antenna switching circuit for switching and connecting a plurality of antennas to a television receiver, and a synchronization signal separation circuit for separating a synchronization signal from a video signal output from the television receiver. In the automatic antenna switching device that performs an antenna search with reference to the sync signal separated by the sync signal separation circuit, when the sync signal cannot be obtained from the sync signal separation circuit,
Equipped with a pseudo-synchronization signal generating means for generating a pseudo-synchronization signal which serves as a reference for the timing of the antenna search, and the pseudo-synchronization signal generating means uses a timer built in the microcomputer and can be generated. An automatic antenna switching apparatus for an automobile, characterized in that the average cycle of the pseudo sync signal is approximated to the correct cycle of the sync signal by combining different cycles in time series. 2. The automatic antenna switching apparatus for an automobile according to claim 1, wherein the antenna search is stopped when the synchronization signal cannot be obtained from the synchronization signal separation circuit many times.