JPS5880939A - Antenna device - Google Patents

Abstract

PURPOSE:To improve deterioration in reception state due to abrupt variation in electric field by switching a current antenna in a reception state to other antenna reception when the varying speed of the envelope detection output of a received signal exceeds a reference value. CONSTITUTION:When the intensity of an electric field is higher than a reference level, a signal level detecting circuit 13 outputs a level 1. In this case, if a received high frequency level varies, the detection output of an envelope detecting circuit 11 varies and when the absolute value of a differential coefficient at a change point of the detection output exceeds the reference value, a speed detecting circuit 12 generates a 1-level output to open an AND circuit 14, thereby inverting the state of an FF15. If a selecting circuit 1 selects a received signal from an antenna A1, a received signal from an antenna A2 is selected through the inversion of the FF15. When the electric field intensity is lower than the reference level to the contrary, the circuit 13 generates a 0-level output and the FF15 is not inverted, so that the selection of a received signal from an antenna is not switched.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna device suitable for application to car radios, car televisions, etc.

When receiving VHF band radio waves (FM radio waves, TV waves) with a car radio or car TV, the VHP band radio waves have short wavelengths and there are almost no terrestrial waves, so the receiver moves with the vehicle. Then, in the fringe area, the input electric field suddenly weakens and the multipath interference suddenly becomes severe, resulting in sound quality deterioration (especially noticeable when receiving stereo broadcasts), first prize deterioration (snow noise, ghost,
synchronization disorder, etc.). A fringe area refers to a receiving area where the electric field strength is 60 dB/m or less, but if the receiving area moves, the electric field strength may be around 40 dB/m or above due to multipaths and the presence of houses, metal poles, etc. along the road. It changes periodically in a range of 20 dB/m. and,
When the electric field strength decreases to about 20 dB/m (trough),
When receiving FM stereo broadcasts, the distortion will be 10% or more, and when receiving television broadcasts, the synchronization of the screen will be disturbed.

Now, Figure 1 shows the input/output characteristics of a typical FM receiver. If a vehicle enters the fringe area while listening under the field strength corresponding to A, and the input to the receiver drops instantaneously to the field strength B, the broadcast being listened to will momentarily change to 8/8.
N deteriorates from 70dB to 45dBK, and the feeder rises and becomes audible. In addition, for FM receivers that have a built-in muting circuit to suppress inter-office noise, the noise level can be improved by changing the electric field from A to B, as shown in the input/output characteristics in Figure 2. The demodulated signal and the signal itself momentarily dropped by 16 dB, making the broadcast being listened to extremely loud.

By the way, the FM modulated wave should not originally contain an AM component, as shown in Figure 3 AIC, but if the electric field strength fluctuates, it will contain an isometric KAM component as shown in Figure 3 BK.
The result is the same as the modulated one. Now, if we perform envelope detection on the human signal in Figure 3 and the signal in Figure B in M3, we will not obtain a detection output in the case of Figure 3A, but in the case of Figure 3B, we will obtain a detection output that corresponds to the electric field fluctuation. This can be done, as shown in Figure 3B.
It is possible to detect the presence of electric field fluctuations in the signal and the amount of the fluctuations.

In addition, due to the nature of VHFHF radio waves, the electric field fluctuations caused by entering the 717-range area are within a narrow range and a
, *. For this reason, for example, when antennas are set up in front and behind a moving car, the one-man antenna can enjoy the strong electric field fluctuations caused by entering the fringe area, while the other antenna can hardly handle it. It is something that I have not received.

In view of these points, the present invention provides an antenna device that can improve the deterioration of receipt sheets due to fundamental electric field fluctuations.
! This is something to be concerned about.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, in the present invention, a large number of antenna elements, for example two antenna elements, are arranged on a vehicle or the like at a desired interval. In Figure 4, Rondo antenna AI is installed at the front and rear of the U.S. military, respectively.
, when A2 is installed. Also, in Figure 5, the power #J
Dipole antennas (finger 11) on the military's 1st part and the rear, respectively.
This is the case when antennas AI and A2 are installed.

Next, an example of the circuit of the antenna device according to the present invention will be explained with reference to FIG. (1) is a selection circuit that selects a received signal from one of the antenna elements A2. This selection circuit fi+ is composed of one mechanical or electronic changeover switch or two attenuators.

(2) shows the receiving circuit as a whole, in this case an FM radio receiving circuit having a muting circuit (not shown). In this receiving circuit 121, +31 is a front end (having a high frequency crystal circuit, a mixer, and a local oscillator), (4) is an intermediate frequency amplifier circuit, and (5)
is FM detection circuit, (6) is stereo demodulation circuit, (7)
, (8) is the left and right audio width circuit, +91,
(1 (l is the left and right speakers. And the selection circuit (
The received signal from 11 is fed to the front end (3).

Oe is a detection circuit that detects the reception state of at least one of the antenna elements AI and A2, and controls the selection circuit based on the detection output.

Next, this detection circuit 1161 will be explained. Intermediate frequency 0 from any amplification stage of intermediate frequency amplifier circuit (4)! The signal is supplied to the envelope detection circuit (IIK), and the wave output at that time is supplied to the speed detection circuit α2.
1 is a circuit that controls the selection circuit (11) by indicating whether or not the speed of level fluctuation of the detection output of the transverse wave circuit O11 has exceeded a reference value. The continuous layer is the reference value (for example, 10 dB)
When this happens, the antenna is busy selecting a received signal from another antenna element.

Figure 7 shows a series of speed detection circuits G21, the +l1lr & output from the transverse wave circuit (Ill) is supplied to the input terminal (c), and this is directly supplied to the inverting input terminal of the arithmetic amplifier @411 bell. , is supplied to the non-inverting input terminal of the operational amplifier a9 via a differentiating circuit (consisting of a resistor 11.0 and a capacitor) U.An output terminal Q4 is derived from the output terminal of the quadrupler a3. In addition, resistor C71, +21
The reference value is determined by the ratio of 1.

Now, as shown in FIG. 1 and C in FIG. 42, when the electric field strength is quite low, noise causes
In order to prevent this, the signal level (strength) detection circuit a3 and the AND circuit 1141
will be established. It should be noted that the switching noise caused by the selection circuit (17) when the pulling field strength is still strong and the signal is good is removed by the limiter output of the intermediate frequency amplification circuit (4), and does not cause any audible problem. .

That is, the intermediate frequency signal from the intermediate frequency amplification circuit (4) is supplied to the signal level detection circuit α3, and the reference level (for example, 1
0dB), pressure is applied to output a detection output of "1". When the detection output of the detection circuit (ill) is equal to or higher than the reference value, the detection circuit (121) outputs the ejection output rlJ by 5I/c.Then, the detection circuit (12+,
Each output of u:a is supplied to the AND circuit UK.

In addition, the selection circuit (1) is a T-type 7-rib 70-tube circuit u5I.
is controlled by the output of 7.
AND circuit a is connected to the T input terminal of lip-flop circuit Q51.
(The output of

Next, let us explain the operation of this antenna device. First, it is assumed that the electric field strength, that is, the level of the intermediate frequency signal, is greater than the reference level. When the level of the received high frequency signal (FM modulated signal) fluctuates as shown in Figure 8, the intermediate frequency signal also fluctuates, and therefore the detection output of the detection circuit αυ changes to 5 as shown in Figure 9. Change. Then, when the absolute value of the differential coefficient of the detection output level Pl, P2 at time tl, 12 exceeds the reference value, a detection output "1" is obtained from the detection circuit u21, and the detection circuit 11. Detection output from 1
1" is obtained, an output is obtained from the AND circuit 141, and the 7 lip-flop circuit (+51 is inverted. Thus, from the selection circuit (1rK, the initial antenna element A1
If one received signal from antenna element A2 had been selected, the signal received from antenna element A2 is now selected by the inversion of the flip-flop circuit ttS.

In addition, if the electric field strength, that is, the level of the intermediate signal, is smaller than the reference level, the output of the detection circuit (131 is "0").
Therefore, even if the detection output rIJ is obtained from the detection circuit (121), the flip-flop circuit θ9 will not be inverted, and the selection of the received signal of the antenna cables AI and A2 will not be switched. A type 7 lip-flop circuit can be used for J- instead of the lip 70 tube circuit + 151 and the AND circuit I. In that case, the detection output of the 1 yellow output circuit a2
-, the clock input terminal preload of the Type 7 flip-flop circuit, and the detection output of the detection circuit I may be supplied to its J and input terminals.

According to the present invention described above, it is possible to obtain an antenna device that can improve reception condition deterioration due to rapid electric field fluctuations.

Note that the mobile object to which the above-described antenna device and receiver (radio receiver, television receiver, etc.) are attached or mounted may be a ship or an aircraft in addition to a vehicle.

Further, the number of antenna elements may also be three or more.

[Brief explanation of drawings]

@Figures 1 and 112 are characteristic curve diagrams showing the input and output characteristics of a radio receiver! ! 3 is a waveform diagram, FIGS. 4 and 5 are a side view and a plan view, respectively, showing the state in which the antenna element used in the present invention is attached to a passenger car. FIG. 6 is a block diagram showing an embodiment of the present invention. 7 and 7 are circuit diagrams showing a part of FIG. 6, and FIG. 8 and FIG. 9 are waveform diagrams. AI, A2 is the antenna element, +13 is the selection circuit, 01
1 is an envelope detection circuit, 0 is a continuous horizontal output circuit, 0 is a signal level (strength) detection circuit, and Q61 is a horizontal output circuit. Input Shib L (dB) - m - Input L Bell (dB) - No.:; shi8 11 a2 About opening - 啼

Claims (1)

[Claims] a plurality of antenna elements arranged at desired intervals; a selection circuit for selecting a received signal from one antenna element among the plurality of antenna elements; and at least one antenna among the plurality of antenna elements. It has a detection circuit that detects the receiving state of the element, and the detection circuit has an envelope detection circuit to which the reception signal of the selected antenna element is supplied, and a speed of level fluctuation of the detection output of the mosquito envelope detection circuit is the standard. and a speed detection circuit for controlling the selection circuit by detecting whether or not the selection circuit has become busier than the reference value. An antenna device characterized in that more received signals are selected.