JPS59198007A - On-vehicle tv receiving antenna with directivity switching - Google Patents

Abstract

PURPOSE:To optimize always the receiving state by using switchingly a unipole antenna having the directivity in left and right directions of a car and a U- shaped antenna having the directivity in forward and backward directions. CONSTITUTION:An output of the unipole on-vehicle TV antenna having higher sensitivity in the left and right directions of a car and an output of the U-shaped on-vehicle TV antenna 2 having higher sensitivity in forward and backward directions are fed to a comparison amplifier 16 respectively via a distributor 10, a buffer 11, a mixer 12, an IF amplifier 14, and a detector 15. A Schmitt circuit 20 is activated in response to the output of the amplifier 16 so as to operate a switch circuit 17. Then, a receiving signal from an output synthesizer 19 is fed to a receiver 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an in-vehicle antenna for receiving VHF and UHF TV broadcasts in a car.

In recent years, TV receivers have become more compact, making it easier to watch TV broadcasts inside a car. Along with this, it has become necessary to have a receiving antenna suitable for use in vehicles.

The size, shape, and installation conditions for antennas mounted on automobiles are determined by considerations such as appearance and traffic safety, and operation under optimal conditions cannot necessarily be expected. Furthermore, since the height of a car is at most 3 meters, incoming radio waves are easily affected by shadows and reflections from buildings, etc., and reception conditions vary significantly depending on the position of the car.

Conventional in-vehicle antennas connect a single antenna with fixed directivity to a TV receiver, and if the direction of arrival of radio waves changes significantly due to the influence of buildings, etc., the receiving screen may collapse and become difficult to watch. There was a problem that disappeared. In addition, there are antennas that change the directivity by remote control to obtain the optimum reception condition, but the directivity is not always optimal, and there is a problem that the directivity has to be changed when the antenna is moving.

The present invention eliminates the above-mentioned disadvantages of conventional antennas, and its purpose is to automatically optimize the reception condition no matter where you move, and to enable you to receive good 7 TV broadcasts in your car. There is a particular thing.

The present invention will be explained in detail below.

FIG. 1 shows an embodiment of the present invention, in which a uniball type in-vehicle TV antenna 1 having directivity with high sensitivity in the left and right directions of the vehicle as shown in FIG. A directional U-shaped in-vehicle TV antenna 2 with high sensitivity, and a feed line 4 connected to each antenna. and a switching combiner 8 that connects the antenna 1 or 2, whichever has a higher signal level, to the output, and connects the output of the switching combiner to the TV receiver 5 to generate local oscillation of the TV receiver. It receives the signal and outputs a TV radio signal. (A patent application has previously been filed for the unipole-type vehicle-mounted antenna and the U-shaped vehicle-mounted antenna.) FIG. 2 shows a block diaphragm of the switching combiner. Signals from the uniball type in-vehicle TV antenna 1 and the U-shaped in-vehicle TV antenna 2 are inputted from the input terminals of ANTl and ANT2, respectively. A part of the TV signal is taken out by the distributor 10 and sent to the buffer 1
Pass through 1 and enter mixer] 2. The signal extracted from the local oscillator of the TV receiver is connected to the
8, it is divided into ANTI and ANT2 mixers.

The IF multiplied signal from the mixer 12 is amplified by the F amplifier 13. Since the dynamic range of TV radio waves is about 60 dB, the compressor 14 compresses the dynamic range to about 20 dB, and the detector 15 converts it into a DC voltage.

By the comparison amplifier 16, ANTI
When the difference between the detected voltage of ANT1 and the detected voltage of ANT2 is less than a certain value, linear amplification is performed, and when the difference exceeds a certain value, an output is obtained which becomes the power supply voltage when ANTl is high and becomes 0 when ANT2 is high. When the output of ANTI and the output of ANT2 are almost equal to E, the two switch quickly and the image quality flickers.
Since it is difficult to see, the switching is stabilized by the effect of the linear amplification part of the comparison amplifier and the Schmitt circuit 20.

Figure 8 shows the hysteresis characteristics of the Seamit circuit.
The output turns on at vth, which is close to the power supply voltage, and V close to 0.
The output is set to turn off at thz. The transition time for switching is set from several μs to several hundred ns, so as to prevent image synchronization from being disturbed. When the differential voltage between ANT1 and ANT2 applied to the comparator amplifier becomes greater than +VD, the input voltage of the Seamit circuit exceeds Vth, so the output becomes a constant voltage ■. is held and does not switch until the differential voltage reaches -VD.

-Vl, the input voltage of the Schmitt circuit exceeds Vthz and the output is held at 0.

Therefore, if you change the gain of the linear amplification part of the comparison amplifier, -
The interval between (1) and (vl) changes, and the hysteresis level difference between the signal levels at which the antenna switches can be set appropriately. One of the outputs of the Schmitt circuit is passed through an inverter 21, so that when ANTI is high, o1 is high, and when ANT2 is high, an output of o1 is produced. Each output is ANTI, AN
This is used as a control signal for the switch circuit 17 of T2, and when the level of ANTl is high, the input signal of ANTI is added to the output synthesizer 19, and when the level of ANT2 is high, the output signal of ANT2 is added and output.

When radio waves arrive from the side as shown by the arrow in Figure 5,
The reception level of the unipole in-vehicle TV antenna connected to the ANT1 end becomes higher than the reception level of the U-shaped in-vehicle TV antenna connected to the ANT2 end, and the signal of the unipole in-vehicle TV antenna is output.

Also, when radio waves arrive from the front as shown by the arrow in Figure 6, the reception level of the U-shaped in-vehicle TV antenna connected to the ANT2 end is the reception level of the 4N level of the unihole-type in-vehicle TV antenna connected to the ANT1 end. The signal from the U-shaped vehicle antenna is output. Also, radio waves arriving from a diagonal direction of a car may be received at the same level by two antennas, but due to the Schmitt circuit, the level of one antenna is slightly higher than the level of the other antenna. Since the antennas have a hysteresis characteristic so that they can be switched at different times, the antennas alternately switch at high speed and do not cause flickering in the image.

As described above, according to the present invention, it is possible to automatically switch the antenna so that the highest signal level can be obtained regardless of whether TV radio waves arrive from the front or rear, right or left direction, and to obtain the optimum reception state. In addition, since the antenna is selected based only on the signal level, regardless of the structure of TV broadcast waves, it can handle any modulated signal and can also handle FM broadcasting.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the TV receiving antenna of the present invention. Figure 2 is a block diagram of the switching combiner, Figures 3, 4 and 4 are diagrams showing the directivity of a unipole antenna or U-shaped antenna, respectively, and Figures 5 and 6 are the arrival direction and directivity of radio waves. Figure 7 is a diagram showing the relationship between the detection voltage and amplified output voltage of both antennas, and Figure 8 is a diagram showing the hysteresis characteristics of the Seamit circuit. Antenna, 2 is a U-shaped in-vehicle TV antenna, 3 is a switching combiner, 4 is a feeder line, 5 is a TV receiver, 6 is a uniball type in-vehicle antenna directivity,
7 shows the directivity of the U-shaped in-vehicle TV antenna. Fig. 1 Fig. 2 1-〇3 Fig. 3 ~ -/-6 Fig. 5

Claims (1)

[Claims] (1) In-vehicle VHF and UHF band TV receiving antennas include a uniball-type in-vehicle T'V antenna that has directivity with high sensitivity in the left and right directions of the vehicle, and a co-vehicle T'V antenna with high sensitivity directivity in the front and rear directions of the vehicle. A portion of the signals received by the in-vehicle TV antenna, the feeder line connected to each antenna, the unipole antenna, and the U-shaped antenna are distributed, mixed with the local signal of the TV receiver, and then After obtaining the frequency and increasing the frequency by 11J and compressing the signal range, it is detected and the DC output voltage according to the received signal level of each antenna is obtained, until the difference between the two DC voltages becomes a constant value. is linearly amplified, and when a constant value occurs, it is passed through a comparator multiplier that becomes the power supply voltage or 0, and then passes through a Schmitt circuit that switches with hysteresis characteristics at the power supply voltage or a voltage close to 0, and the output of the Schmitt circuit is is divided into two, one is connected to a switch circuit that turns on and off the input signal of one antenna, and the other is connected through an inverter to a switch circuit that turns on and off the input signal of the other antenna, and the output signals of both switch circuits are connected. and a switching combiner that guides the signal to the output combiner and takes out the output.