JPS5974708A - Traveling object mounted television receiving antenna device - Google Patents

Abstract

PURPOSE:To prevent the generation of a fading phenomenon and to obtain easy-to-see pictures by setting the upper limit value of the detecting output level and selecting an antenna showing the highest detecting output level among antennas or synthetic antennas showing a detecting output level lower than said upper limit value. CONSTITUTION:A detecting output level at which a using TV picture receiver produces a cross modulation is set at a reference level setter 40 of a TV receiving antenna device which is mounted on a traveling object. A synchronizing signal (a) sent from the TV picture receiver is applied to a control signal generator 31 to produce a sampling signal (b). Then the antennas which are connected to the picture receiver are selected successively for switch or synthesization by a switch 30. At the same time, a receiving level signal (c) is applied to storage circuits 32-34, and the detecting output level is stored in accordance with the antenna switching timing under the control of the generator 31. A level comparator 35 compares the stored detecting output level with the output level of the level setter 40. Then the switch 30 is controlled only when the detecting output level is lower than the set value. Thus, the generation of a fading phenomenon is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiving antenna device mounted on a mobile body such as a vehicle-mounted television.

When receiving TV broadcast waves using an in-vehicle TV antenna mounted on a mobile object such as a car, ghost interference due to foul waves from the ground or high-rise buildings, etc., and fading due to interference with direct waves from the transmitting antenna occur. Sometimes.

Conventional car TV antennas that use a single antenna directly receive such ghost disturbances and fading, so when the vehicle carrying the antenna moves, these disturbances appear on the screen and cause ghosting. , flutter phenomena, and out-of-synchronization occurred, making it extremely difficult to see.

Furthermore, even in a stationary state, poor reception occurred when the receiving antenna was placed at the trough of the standing wave.

Several methods have been devised to resolve such poor reception in mobile bodies.

One method is to use multiple antennas (1) as shown in Figure 1.
12.13 A method of arranging antennas with different positions and antenna orientations, selecting the antenna with the maximum reception level from the plurality of antennas using the switching controller 14, and connecting it to the television receiver 15. It is.

Another example, as shown in FIG. 2, uses an antenna system 26 having two or more antennas, and selects and combines some of these antennas with a switching controller 24 to create a plurality of composite antennas.・This is a method in which a pattern can be formed, and the combination with the maximum reception is selected from among the combinations of antenna selection and synthesis, and the combination is connected to the television receiver 15.

Now, in conventional vehicle antenna systems, whether using the above-mentioned spatial diversity method or variable directivity antenna method, the antenna that provides the maximum receiving antenna output is selected and connected to the television receiver. It is a method.

However, with this maximum receiving antenna selection method, there is no problem with reception in areas with low receiving field strength, but in areas with strong electric fields near the transmitting antenna, the input to the TV receiver becomes excessive, resulting in cross-modulation, which significantly degrades the reception quality. It may become defective. In such a case, selecting the antenna that provides the maximum reception level will cause cross modulation.

The present invention describes the cross-modulation phenomenon under a strong electric field with respect to a directional variable antenna system.

In FIG. 1, reference numerals 11 to 13 indicate a plurality of antennas installed at different positions or with different pointing directions, and the outputs of the antennas are connected to the switching controller 14 via feed lines.

In the switching controller 14, the output of any one of the antennas 11 to 13 is connected to the television receiver 1 also installed in the vehicle IO.
It is switched using a switch circuit or the like so that it is connected to the antenna input circuit No. 5.

The detected output television video signal and synchronization signal are extracted from the television receiver 15 and guided to the switching controller 14 . The switching controller 14 performs sampling to sequentially switch the antennas 11 to 13 at regular intervals in synchronization with the TV synchronization signal, etc., at a timing that does not adversely affect the image of the TV '1Ji 15. During this sampling, the detection output levels of each antenna when connected to the television receiver 15 are compared, and the antenna with the highest level is connected to the television receiver for a certain period of time until the next sampling is performed. The switching controller 14 is switched so that the connection is made.

The timing of this sampling is performed, for example, within the vertical retrace period of the television signal, and the antenna with the maximum reception level at the time of the previous sampling continues to be connected to the television receiver 15 until the next vertical retrace period.

In FIG. 2, 26 is a variable-directivity antenna system that combines a plurality of antennas, and its output is also connected to the switching controller 24 via a feed line.

The directivity of the variable directivity antenna system 260 can be controlled by sending a switching signal from the switching controller 24 to the antenna system through a switching signal line, for example, if the antenna system itself can select and combine antennas to change the directivity. Sent. In addition, if the antenna system itself does not have the selection/synthesis function, this function is included in the switching controller 24, and feed lines are connected from each antenna making up the antenna system to the switching controller 24. Ru.

In this case, as in the case of the example in Figure 1, each antenna is selected and combined within the sampling period, the detection output level in each case is compared, and the highest reception level at this time is used until the next sampling period. The selected/combined antenna is connected to the television receiver 15.

That is, in both of the above two examples, the antenna or composite antenna that provides the maximum reception level is selected and connected to the television receiver.

FIG. 3 is a block diagram showing an example of the configuration of a switching controller, in which a and c are respectively a synchronization signal and a received detection level signal input from a television receiver, b is a signal that controls the switching device 30, and d is the input from the antenna to the switching device 30, and e is the output to the television receiver.

In the case of a variable directivity antenna in which selection and combination are performed within the antenna itself, the switch 3o is included within the antenna.

Now, the control signal generator 81 is switched, and a sampling signal is output as a control signal for the device 3o, so that the plurality of antennas 11 to 13 are connected one by one to the television receiver 15 at a constant period. Control switch 3°. However, when using variable directivity antennas, the constituent antennas are sequentially selected and combined within the switch 8o.

The detection output level of the television signal is stored in the level storage circuit 32, 83, 84 in synchronization with the antenna switching within one sampling signal period, and this value is held until the next sampling. The stored detection output levels are compared for each sampling signal in the level comparison circuit 35, and the count number of the circuit with the highest level is incremented by one. ■At the end of multiple samplings included in a sampling period, the counts of these counters are compared by the count comparison circuit 39, and the antenna with the highest count is used as the TV receiver until the next sampling period]5
The switch 3o is controlled so as to be connected to.

When performing level comparison only once in one sampling period, the counters and count number comparison circuits 36, 37, and 38 in FIG. 3 are unnecessary, and the control signal generator 31
inputs the comparison result from the level comparison circuit 35 and determines antenna selection.

FIG. 4 shows an embodiment of the present invention. In order to avoid cross-modulation on the television receiver due to excessive input, excessive input is detected and the antenna is prevented from being connected to the television receiver.

In FIG. 4, 40 is a reference level setter, which sets the detection output level value at which the television receiver used starts to cause cross modulation.

The switching device 30 is controlled by the control signal generator 81, and the antennas connected to the television receiver are sequentially selectively switched or selectively synthesized based on the sample signal.

The detected output level of the television signal is stored and held in each level storage circuit in synchronization with antenna switching within the sampling signal. The stored detection output level is compared for each sampling signal in the level comparison circuit 35. At this time, it is also compared with the level value input from the reference level setter 4.0, and if the detection output level exceeds this level value, In this case, the detection output level is ignored and excluded from comparison and selection. The subsequent operation is similar to that of the circuit shown in FIG.

By doing this, as long as the set level value sent from the reference level setter 40 to the level comparator 35 is set below the level at which the television receiver starts to cause cross modulation, it is possible to avoid excessive noise that causes cross modulation. There is no need to connect human power to the television receiver, and therefore the occurrence of cross modulation can be suppressed.

Actual television receivers have individual differences in the input level at which cross-modulation occurs due to variations in characteristics, but in this case, the set level value of the reference level setter 40 can be made variable and the set value can be changed manually. It is a good idea to keep it like this.

[Brief explanation of drawings]

1 and 2 are block diagrams of a conventional television receiving antenna device mounted on a mobile body, FIG. 3 is a block diagram of a conventional switching controller, and FIG. 4 is a block diagram of a conventional television receiving antenna device mounted on a mobile body. 1 shows a configuration block diagram of a switching controller used in a television reception antenna device. In the figure, 11112.18 is an antenna, 14 is a switching controller,
15 is a television receiver, 30 is a switch, 31 is a control signal generator, 32, 33, 34 is a level storage circuit, 35 is a level comparison circuit, 36, 37, 38 is a counter, 39 is a count number comparison circuit, 40 is a reference level setter. 71 figure 72 figure 0

Claims (2)

[Claims] (1) Select one of the multiple television receiving antennas mounted on the mobile body and the outputs of these antennas, or select and combine two or more antennas, and send the output to the mobile body. The antenna input circuit I/ζ of a television receiver mounted on (In a television reception antenna device having a switching controller in which an antenna with a high M level is connected to the antenna input circuit for the primary television reception and maintains that state until the next sampling period, the detection An upper limit value is set for the output level, antennas or composite antennas that exceed the upper limit are excluded from selection, and the antenna that exhibits the maximum detection output level is selected from among the antennas or composite antennas that exhibit a detection output level below the upper limit value. What is claimed is: 1. A television reception antenna device mounted on a mobile body, characterized in that the antenna device is connected to the television receiver. (2) The television reception antenna device for mounting on a mobile object according to claim (1), wherein the setting of the upper limit value of the detection output level is manually variable.