JPS5829227A - Diversity receiver - Google Patents

Abstract

PURPOSE:To increase a diversity effect by switching antenna elements wherein directivity in horizontal planes is valued highly and antenna elements wherein sensitivity in horizontal planes is valued highly in the best state. CONSTITUTION:An attenuation controlling circuit 23 compares an input signal level with a preset reference voltage to decided on whether the input signal level is high or low, and attenuators 10 and 11 are interposed between a changeover switch and antennas 2 and 3 whose reception sensitivity is valued highly at an intense-electric-field place where an SN ratio is not so important. Therefore, antennas 1 and 4 having highly valued directivity in horizontal planes and said antennas 2 and 3 do not have a great difference and the probability that the directivity-valued antennas 1 and 4 useful for the removal of a ghost are switched is increased. When electric field intensity is low, on the other hand, said attenuators 10 and 11 are not added, so the probability that the sensitivity- valued antennas 2 and 3 are selected is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diversity receiving device suitable for a television receiver mounted on a moving body such as an automobile.

Conventional receiving antenna devices for television receivers mounted on mobile objects such as automobiles are either antennas whose directivity in the horizontal plane is close to omnidirectional, or antennas whose directivity in the horizontal plane is close to omnidirectional. There are some antennas that can be manually switched using a combination of antennas with different characteristics, but they have problems with operability while driving, and furthermore, ghost flutter phenomenon due to the influence of reflected waves makes it difficult to receive good reception. there were.

Switched diversity reception, which automatically switches between multiple antennas with unidirectionality in the horizontal plane, is effective as a method to improve these problems. However, since it is difficult to achieve both horizontal reception sensitivity and unidirectional characteristics while being small because it is installed on a moving object, there are two types of antennas: one that emphasizes horizontal reception sensitivity and the other that emphasizes horizontal unidirectionality. When multiple antennas are used as receiving antennas and switching diversity is performed by level comparison, ghosts,
Effective against flutter phenomenon. However, unidirectional antennas have lower reception sensitivity in the horizontal plane than antennas that emphasize reception sensitivity in the horizontal plane, so the probability of switching is low, making it impossible to perform diversity reception that fully utilizes the characteristics of the antenna.

The present invention is intended to solve the above problems, and embodiments thereof will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, among receiving antennas 1.2 and 3.4, antennas 1 and 4 place emphasis on unidirectionality in the horizontal plane, and antennas 2 and 3 place emphasis on receiving sensitivity in the horizontal plane. The high-frequency signals 6, 8 received by the antennas 1, 4, which emphasize unidirectionality in the horizontal plane, are switched by a changeover switch made of a transistor or diode, and the high-frequency signals 6, 8, which are received by the antennas 2, 3, which emphasize the receiving sensitivity in the horizontal plane, are ,
It passes through attenuators 10 and 11 controlled by control signal 9 and is input to changeover switch 12 .

The changeover switch 12 is a diversity reception control circuit 17
The drive signals 18, 19, 20, and 21 are automatically switched to the high-frequency signal 13 from the antenna with a high reception level, and the high-frequency signal 13 is input to the antenna input terminal of the television receiver 14. Television receiver 14. From there, a vertical synchronization signal 16 is sent to the diversity reception control circuit 17 as a control timing reference signal necessary for diversity reception control, and a television +37 video signal is sent as a reception level signal for detecting the instantaneous reception level of each antenna. 16 is sent from the television receiver 14 to the attenuator control circuit 23. The attenuator control circuit 23 sends a signal 22 indicating the average electric field strength such as the AGC voltage. It determines whether the input signal level of the attenuator control circuit 23 is high or low compared to the level of the input signal, and in places with strong electric field strength where the S/N ratio is not a big problem, the antenna and changeover switch 120 are designed to emphasize reception sensitivity in the horizontal plane.
A control signal 9 is output so that an attenuator 10.11 is inserted between the two. The high frequency signals 6 and 7 received by the antenna that emphasizes reception sensitivity in the horizontal plane are attenuated by the attenuator 10.1.
Antenna 1 with attenuation in 1 and emphasizing unidirectionality in the horizontal plane,
The superiority of the reception level compared to the high frequency signals 6 and 8 received by antenna 4 is lost, and the probability of switching to antennas 1 and 4 that emphasize unidirectionality in the horizontal plane increases. In other words, in places where the electric field strength is strong, the influence of reflected waves is relatively small.
Enables reception with less ghost and flutter phenomena. Also.

When receiving with an antenna that emphasizes reception sensitivity in the horizontal plane,
Although the level of the received high-frequency signal is lowered by adding an attenuator, the deterioration of the S/N ratio does not become a problem in places where the electric field strength is strong. When the electric field strength is weak, the control signal 9 from the attenuator control circuit 23 is used to switch between the antennas 2 and 3 that emphasize sensitivity in the horizontal plane. attenuator 10 between
．． 11 is not added, and antenna switching is controlled based on the signal level received by each antenna as it is.

FIG. 2 is a graph showing the relationship between electric field strength and AGC voltage.

FIG. 3 shows a specific circuit example of the attenuator control circuit 23 and attenuator 10.11 shown in FIG. Obtain appropriate voltage characteristics corresponding to the intensity of the stain field. In the level comparison circuit C, the reference voltage for level comparison has hysteresis, and when the input voltage moves from a high voltage to a low voltage, the output of the level comparison circuit C in the initial state is a low voltage, so the diode D is reversed. The reference voltage vs for level comparison with bias is the power supply voltage element B connected to resistors R2, R3, R
It is determined by the partial pressure ratio divided by 4. That is, when the input voltage becomes lower than the voltage of v8, the output of the level comparison circuit C becomes a high potential. Conversely, if we consider the case where the input voltage changes from a low voltage to a high voltage, the output of the level comparator circuit C is at a high potential in the initial state, so the diode D is not forward biased.

Current flows into resistor R4 through resistor R6, and resistor R4
The current flowing through increases, the potential at the 0 point rises, and the resistance R2
The reference voltage v8 for level comparison also increases due to the voltage division ratio of R3 and R3. In other words, unless the input voltage becomes higher than v8, the output of the level comparison circuit C will not become a low potential.

FIG. 4 is a graph showing the relationship between the input voltage and output voltage of the level comparison circuit C. When the input voltage changes from a low voltage to a high voltage, it follows a trajectory of H, and when the input voltage changes from a high voltage to a low voltage, it follows a trajectory of 1. Providing such hysteresis prevents the level comparison circuit from chattering when the input voltage is close to the reference voltage for level comparison.

A switch circuit is driven by the output signal of the level comparison circuit C, and an attenuator E is controlled by the output signal of the switch circuit. The attenuator E is provided between the receiving antenna and the changeover switch, and is composed of capacitors C2 and C3 for DC blocking, a resistor R for attenuating high frequency signals, and a diode D2 for bypassing the resistor R8. ing. Note that a resistor R,,, is connected to one negative terminal of the diode D2.
The divided pi and as voltages are applied through R7, and the control signal from the switch circuit is input to the other terminal. Assuming that the electric field strength is strong, the output of the level comparison circuit C will be at a low potential and the output of the switch circuit will be at a high potential, and the resistor R8
The diode D for bypass is not reverse biased, and the high frequency signal from the antenna 2 passes through the resistor R8 and the attenuated signal is transferred to the switch 1.
2. Conversely, when the electric field strength is weak, the output of the switch circuit is at a low potential and the diode D2 becomes forward biased, and the high frequency signal from the antenna does not pass through the resistor R8, but is bypassed by the diode D2 and sent to the changeover switch 12.
is input to.

As is clear from the above explanation, the present invention can perform diversity reception that makes good use of the directivity characteristics and reception sensitivity characteristics of the receiving antenna depending on the electric field strength, and in particular improves television reception in mobile objects by eliminating ghosts and flutter. It can be made less stable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between electric field strength and AGC voltage, and Fig. 3 is an attenuator control circuit and a specific circuit of the attenuator that can be used in the present invention. A wiring diagram showing an example, and FIG. 4 is a characteristic diagram showing the relationship between the input voltage and the output voltage of the level comparison circuit of the attenuator control circuit. 1-4 , , , , 77 tena , 10 , 11 , ,
, , Attenuator, 12... Changeover switch, 14
...television receiver, 17,...
, Diperity reception control circuit, 23. , Attenuator control circuit. Name of agent: Patent attorney Toshio Nakao and one other famous person
1 cause

Claims (1)

[Claims] A diversity receiving device configured to select the antenna with the highest level from high frequency signals received by a plurality of antennas and switch to that antenna using a changeover switch, the device comprising a plurality of antennas with high reception sensitivity in the horizontal plane; multiple antennas having unidirectionality in the horizontal plane;
a circuit that adds an attenuator using a semiconductor switch to attenuate the signal received by the antenna with high reception sensitivity in the horizontal plane;
Detects the average level of received electric field strength, compares whether the detected signal is larger or smaller than a preset level, and controls the semiconductor switch using the compared signal to add or not add an attenuator. and the attenuator control circuit operates according to the electric field strength, and the attenuator controlled by the attenuator control circuit is configured to switch the attenuator controlled by the attenuator control circuit to the antenna with high reception sensitivity in the horizontal plane. 1. A diversity receiving device connected between two switches, and configured such that a signal received by the antenna having unidirectionality in the horizontal plane is directly input to the changeover switch.