JPS626582A - Antenna changeover device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a picture quality of a received picture by changing over an antenna only when a difference between the output of a level detecting means for extracting a signal level of the antenna and the level deciding the antenna used at that time exceeds a value determined by a level difference setting means. CONSTITUTION:The receiving level of respective antennas is extracted in a level detecting gate circuit 8, passes through a level difference setting circuit 10 and is inputted to a level comparison circuit 12. The level comparison circuit 12 compares the output of the level difference setting circuit 10 with an output of a level sampling hold circuit 7 and outputs a pulse of high level only in an interval indicating the high level of the output of the level difference setting circuit 10. When viewing from the level comparison circuit 12, the level difference is constantly added to the output from the level detecting gate circuit 8 by a resistance division with respect to a hold level of the level sampling hold circuit 7. Thereby, a frequency changeover of the antenna for a small change of an electric field can be stopped by a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an antenna switching device for a vehicle, and particularly to a reception level comparison circuit thereof.

B. Overview of the Invention In the antenna switching device according to the present invention, the difference between the output of the V-pel detection + stage for extracting the signal level of each antenna and the level determined for the antenna being used at that time is determined by the level difference setting means. Antenna switching takes place only once the set value is exceeded.

C. Conventional technology When receiving television in a moving object such as a vehicle, multiple techniques propagate between direct waves from the broadcasting station and reflected waves due to the influence of geographical conditions and buildings, resulting in fluctuations in reception. , deterioration of image S/N and flutter phenomenon appear, which eventually leads to image synchronization disturbance.

Therefore, in order to reduce reception disturbances in mobile reception as much as possible, diversity reception is used in which multiple receiving antennas are placed on the wheels at intervals that do not cause mutual interference, and control is switched to the antenna with the best reception condition. has been widely adopted.

Comparison of reception levels of each antenna and antenna switching in such diversity reception are disclosed in Japanese Patent Laid-Open Nos. 12438 and 12439.

D Problems to be Solved by the Invention In such an antenna switching device, if the difference in the level of the received electric field of the antenna for each l field is minute, 1
The antenna is switched to the maximum reception level for each field, which may actually impair the quality of the received image.

In such a case, it is preferable to stop antenna switching when there is a minute difference in electric field level.

An object of the present invention is to enable the reception level of other antennas to be greater than a certain value with respect to the reception level of the antenna currently receiving, using a simple circuit, without being limited by the number of antennas for reception. An object of the present invention is to provide an antenna switching device that switches to that antenna only at a moment's notice.

In order to achieve the above object, the present invention includes a level detecting means for extracting the signal level of each antenna switched to the vertical line period circle of the video signal, and a means for holding the antenna signal level. and a means for comparing the level of each antenna signal received next with the signal held in the holding means, further capable of setting a level difference in each of the compared signals. The provision of level difference setting means is supported. It is also possible that the above level difference setting means is located on the level extraction side.l Field City Antenna @
It is also true that it is a means of holding the name.

F The action level difference setting + stage is a device 1f that imitates the conventional reception level comparison circuit and stops antenna switching in response to small electric field changes.
Add example fl.

G Practical Figure 1 is a block diagram showing the configuration of a wheel antenna switching device used in a television receiver 1' equipped with a video output line terminal. Although any number of antennas can be cut, the figure shows a case of four antennas. In the figure, the part surrounded by thick lines is the antenna switching device, and the part surrounded by dotted lines is the reception level comparison circuit.

The antennas ANT-1, 2, 3, and 4 are connected to a high-frequency switch Ml that switches to the best receiving antenna via a coaxial cable A4, and the switching output is connected to the antenna input terminal of the TV receiver 2 via a coaxial cable B. Connected. The video signal detected by the television receiver 2 is output to the antenna switching device through a coaxial cable C connected to a video output line terminal.

The video signal input to the antenna switcher is input to the video amplification circuit 3. The video output is synchronously separated by a synchronous separation circuit 4, and further divided into a horizontal synchronous timing pulse 5 and a vertical synchronous timing pulse 6Vc, which are input to a control circuit 16 that generates timing pulses necessary for antenna switching, level detection, etc.

On the other hand, the video signal output from the video amplification circuit 3 is transmitted to each anti-7 at the timing shown in FIG.
/M period, and appears as a signal [Figure 2 (dJ)] containing a video change that is equal to the reception level of each antenna. Change CN3 (d) that is equal to the reception V level of the switched antenna. ] can be obtained as is in about 13 μs.
Switch each antenna within a short interval of 8 he switch circuit 1
This is because the AGC of the television receiver does not respond because the switch is made in .

This video value +:id is simultaneously input to the level sampling and holding N path 7 and the level detection gate circuit 8.

A level detection pulse 9 is manually applied to the level detection gate circuit 8 at the timing shown in FIG. 2 in order to detect the reception level of each antenna in the video signal d. Level detection occurs at the trailing edge of the antenna switching pulse. This is because there is a time delay of about 2 μs from the high frequency switch circuit 1 until the video is detected by the television receiver 2. At this time, the reception level of each antenna is extracted by a level detection gate circuit 8, and input to a level comparison circuit 12 through a level difference setting circuit 1o.

On the other hand, the sampling and holding operation of the video signal manually input to the level sampling and holding circuit 7 is performed as follows. First, reset pulse 1 shown in Figure 2]
Since the output is reset at low level, the output is input to the level comparison circuit 12 at a low level.

At the same time, the level comparison circuit 1 comes from the V-pel difference setting circuit 10.
The input level of No. 2 always indicates a high level, and the level comparator circuit 12 outputs a high level with the level detection gate pulse width. In this way, the level comparison circuit 12 is configured as a level difference setting circuit I.
The output of the level difference setting circuit 10 is compared with the output of the level sampling and holding circuit 7, and the level comparison circuit 12 outputs a cylinder-level pulse only during the period in which the output of the level difference setting circuit 10 is at a high level. By using this high level pulse output as the sampling and holding pulse 13 of the level sampling and holding circuit 7, the first antenna reception level is sampled and held.

When the reception level of the first antenna is sampled and held, this hold level is sequentially compared with the reception level of the fourth antenna of 2.3 degrees, and the level comparison circuit 12 selects a high level for the antenna that shows a level higher than the hold level. A level pulse is output, and the hold level of the level sampling hold circuit 7 is replaced with a new one. Therefore, the output of the level sampling and holding circuit 7 always holds the level of the maximum receiving antenna immediately before being reset. In addition, the output of the level comparison circuit 12 is inputted to the Kakunta decoder circuit 14, which selects the antenna with the highest reception level among the antennas using the control clock 15 output from the control circuit 16, and corresponds to each antenna. Signal Q□.

Q2 + Q3 p Q4 (see Figure 2) is output. In this way, the output pulse of the level comparison circuit is outputted at a position corresponding to which antenna within the received level detection horizontal interval (IUH), and the output pulse is determined by the power-wander decoder 14 to determine which antenna is the maximum receiving antenna. decide.

FIG. 2 shows the timing when ANT-1 is held at the maximum reception level. Further, the antenna level comparison operation is performed sequentially starting from the antenna selected in the previous field, as shown in Table 1.

Kawanta decoder episode! Output signal Q1 p of Rr14
Q2 pQ3. Q4 is manually inputted to the high frequency switch drive circuit 17, and its output drives the high frequency switch circuit 1.

As described above, antenna switching and level detection using a high frequency switch are performed using one level detection gate circuit 8.
, level sampling and holding circuit 7 and level comparison circuit 7 are processed in series in time, so even if the number of antennas for diversity increases, changes to the circuit corresponding to the number of antennas are independent of the configuration of the received level comparison circuit. becomes.

Table 1 Receiving Antenna Level Comparison) @IntroductionHere, the operation of the level difference setting circuit 10 will be explained.@Without this level difference setting circuit 10, the operation of the level comparison circuit 12 is dependent on the level sampling and holding circuit 7 and level detection. The respective outputs of the gate circuits 8 will be directly compared.

In this case, as described above, the quality of the received image may be deteriorated. Therefore, according to the present invention, the reception level t of the antenna selected in the previous field is detected at the beginning of the next field, and the levels of other reception antennas are differentiated from that level.

That is, from the perspective of the level comparator circuit 12, the output from the level detection gate port 8 is always divided by the level difference N from the hold level of the level sampling and hold circuit 7 by resistance division. The level difference setting circuit 10 is a circuit for dividing the output level of the level detection gate circuit 8 using an n'' variable resistor and a fixed resistor, which enables arbitrary level difference setting.

FIG. 3 is a specific circuit diagram of the reception level comparison circuit.

As described above, frequent antenna switching in response to minute electric field changes can be stopped with a simple circuit.

As another method, the V-Pell difference setting circuit 10 may of course be added to the output side of the level sampling and holding circuit 7 instead of the output side of the level detection gate circuit 8.

Although the present invention has been described above using a system using a television receiver with a video output line terminal, it is of course possible to incorporate the antenna switching device according to the present invention into the television receiver.

As explained in detail about the invention H, according to the present invention, there is no limit to the number of antennas for communication reception, and it is possible to add the function of stopping antenna switching in response to minute electric field changes with a simple circuit. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a vehicle antenna switching device that uses a television receiver with a video output line terminal.
FIG. 2 is a timing diagram of a video signal and an antenna switch drive pulse, and FIG. 3 is a circuit diagram of a reception level comparison circuit. l...High frequency switch circuit, 2...TV receiver,
3... Video tank @ circuit, 4... Synchronous separation circuit, 5...
・Horizontal synchronization timing pulse, 6... Vertical synchronization timing yf pulse, 7... Level sampling halt circuit, 8... V # detection circuit, 9... Level detection pulse, 10... Leher Difference alf constant circuit, 11.
...Reset pulse, 12...Level comparison circuit, I3
... Sampling hold pulse, 14... Counter decoder circuit, 15... Control clock, 16.
... Control circuit, 17... High frequency switch drive - Video path.

Claims (1)

[Scope of Claims] Level detecting means for extracting the signal level of each antenna switched within the vertical retrace period of the video signal, means for holding the antenna signal level, and the level of each antenna to be received next and the holding. and means for comparing signals held in the means, further comprising: (a) level difference setting means capable of setting a level difference between the signals to be compared. Switcher.