JPS6216057B2 - - Google Patents

Description

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

Conventional receiving antenna devices for television receivers mounted on mobile objects such as automobiles include antennas with horizontal directionality that is close to omnidirectional, or antennas with horizontal directionality that is close to omnidirectional. There are some models that manually switch the combination of antennas held by the vehicle, but there are problems with operability while driving, and furthermore, there is a problem that ghost flutter phenomenon due to the influence of reflected waves makes it difficult to receive good reception. Ta.

An effective way to improve these problems is to use switched diversity reception, which automatically switches between multiple antennas that have unidirectionality in the horizontal plane. However, since it is difficult to achieve both reception sensitivity and unidirectional characteristics in a small size due to the condition of installing it on a mobile object, we have developed antennas that emphasize omnidirectional reception sensitivity and unidirectionality in the horizontal plane. When multiple antennas are used as receiving antennas and switching diversity is performed by level comparison, it is effective for ghost and flutter phenomena. However, unidirectional antennas have lower reception sensitivity in the horizontal plane than omnidirectional antennas that emphasize reception sensitivity, so the probability of switching is low, and diversity reception that takes full advantage of the antenna characteristics cannot be achieved.

The present invention solves the above problems,
Examples 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, 3, and 4, antennas 1 and 4 place emphasis on unidirectionality in the horizontal plane, and antennas 2 and 3 place emphasis on omnidirectional reception sensitivity. The high-frequency signals 5, 8 received by the antennas 1, 4, which emphasize unidirectionality in the horizontal plane, are directly input to the changeover switch 12, which is made of a transistor or diode. The high frequency signals 6, 7 received at 3 are input to a changeover switch 12 through attenuators 10, 11 controlled by a control signal 9. The changeover switch 12 receives drive signals 18, 19, 2 from the diversity reception control circuit 17.
0, 21, the signal is automatically switched to the high frequency signal 13 from the antenna with a high reception level and is input to the antenna input terminal of the television receiver 14. From the television receiver 14 to the diversity reception control circuit 17, a vertical synchronization pulse signal 15 is sent as a control timing reference signal necessary for diversity reception control, and a television signal is sent as a reception level signal for detecting the instantaneous reception level of each antenna. Jiyoung video signal 16 is sent. A signal 22 indicating average electric field strength such as AGC voltage is sent from the television receiver 14 to the attenuator control circuit 23. The attenuator control circuit 23 determines whether the input signal level of the attenuator control circuit 23 is high or low by comparing it with a level corresponding to the electric field strength set in advance, and determines whether the input signal level of the attenuator control circuit 23 is high or low by comparing it with a level corresponding to the electric field strength set in advance, and determines whether the input signal level of the attenuator control circuit 23 is high or low. In this case, a control signal 9 is outputted so that attenuators 10 and 11 are inserted between the omnidirectional antenna and the changeover switch 12, which emphasizes receiving sensitivity. High frequency signals 6 and 7 received by antennas that are omnidirectional and emphasize receiving sensitivity are attenuated by attenuators 10 and 11, compared to high frequency signals 5 and 8 received by antennas 1 and 4 that emphasize unidirectionality in the horizontal plane. The superiority in reception level disappears, and the probability of switching to the 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, allowing reception with less ghost and flutter phenomena. Furthermore, when receiving with an omnidirectional antenna that emphasizes reception sensitivity, the level of the received high-frequency signal will be lowered by adding an attenuator, but in places with strong electric field strength, the deterioration of the SN ratio will not be much of a problem. When the electric field strength is weak, a control signal 9 from an attenuator control circuit 23 is used to switch antennas 2 and 3 that are omnidirectional and emphasize reception sensitivity and a changeover switch 12.
Attenuators 10 and 11 are not added between the antennas, 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 attenuators 10 and 11 shown in FIG.
A ripple component is removed from the AGC voltage signal by an integrating circuit A, and an appropriate voltage characteristic corresponding to the electric field strength is obtained by a DC amplifier circuit B. In the level comparison circuit C, the reference voltage for level comparison has hysteresis, and when the input voltage changes 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 _D1 is reversed. The reference voltage V _s for level comparison with bias is the resistance of the power supply voltage +B.
It is determined by the partial pressure ratio divided by R ₂ , R ₃ , and R ₄ . In other words, when the input voltage drops below this V _s voltage,
The output of level comparison circuit C becomes 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 _D1 becomes forward biased, and current flows into the resistor _R4 through the resistor _R5 . flows in,
The current flowing through resistor R ₄ increases, the potential at point G rises, and the reference voltage V _s for level comparison also rises due to the voltage division ratio of resistors R ₂ and R ₃ . In other words, unless the input voltage becomes higher than this _Vs , 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 moves from a resistance voltage to a high voltage, it follows the trajectory H,
When the input voltage moves from a high voltage to a low voltage, I
passes through the trajectory of 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 D 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 D. Attenuator E is provided between the receiving antenna and the changeover switch, and includes capacitors C ₂ and C ₃ for DC blocking, a resistor R ₈ for attenuating high frequency signals, and a diode D for bypassing the resistor R ₈ . It is composed of ₂ . In addition,
A bias voltage divided by resistors R ₆ and R ₇ is applied to one terminal of the diode D ₂ , and a control signal from the switch circuit D is applied 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 D will be at a high potential, and the diode _D2 for bypassing the resistor _R8 will be connected.
is reverse biased, and the high frequency signal from the antenna passes through resistor R ₈ and the attenuated signal is input to changeover switch 12 . Conversely, when the electric field strength is weak, the output of switch circuit D is at a low potential, and the diode
D ₂ is forward biased, and the high frequency signal from the antenna does not pass through resistor R ₈ but is bypassed by diode D ₂ and input to changeover switch 12 .

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

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure is a characteristic diagram showing the relationship between electric field strength and AGC voltage.
Fig. 3 is a wiring diagram showing a specific circuit example of an attenuator control circuit and an attenuator that can be used in the present invention, and Fig. 4 is a characteristic diagram showing the relationship between the input voltage and output voltage of the level comparison circuit of the attenuator control circuit. It is. 1 to 4... antenna, 10, 11... attenuator,
12... Changeover switch, 14... Television receiver, 17... Diversity reception control circuit,
23...Attenuator control circuit.

Claims (1)

[Claims] 1 From high frequency signals received by multiple antennas,
The diversity receiving device is configured to select the antenna with the highest level and switch to that antenna using a changeover switch. , a circuit that attenuates the signal received by the omnidirectional antenna by adding an attenuator using a semiconductor switch, and detects the average level of the received electric field strength, and the detected signal is larger than a preset level. and an attenuator control circuit for controlling the semiconductor switch with the compared signal to add or not add an attenuator, and the attenuator control circuit the attenuator, which is operative and controlled by an attenuator control circuit, is connected between the omnidirectional antenna and the changeover switch, and the signal received by the horizontal unidirectional antenna is directly connected to the changeover switch; A diversity receiving device characterized in that it is configured to input to a switch.