JPS6234300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving device using a glass antenna for radio reception etc. provided on a window glass of an automobile, and is particularly suitable for use in a diversity receiving system.

When a moving car receives radio waves such as FM broadcasts, periodic fading occurs due to fluctuations in the field strength of the received radio waves in the direction of travel, and multipath distortion occurs due to movement of the receiving point. The quality of the received sound is likely to deteriorate due to fluctuations, etc. In particular, the received sound may become "busy" and cut off in short periods, making it difficult to recognize the received content.

The present invention provides a receiving system that solves this problem, and in particular, performs directional diversity reception by utilizing the difference in directivity of received outputs derived from two different points on one antenna line. The reception output is derived from a position where the output circuits connected to the two points do not affect each other's directional characteristics.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view and an electric circuit diagram of a rear window glass of an automobile showing a first embodiment of the present invention. A rear window glass 1 of an automobile shown in FIG. 1 is provided with a heating conductive wire group 2 for anti-fogging purposes, and these conductive wire groups are formed in a U-shaped pattern. The group of wires is short-circuited at the bus bar 6, and a heating current is passed from the battery 3 through the switch 4 and the bus bars 5 and 7. In order to keep the heating conductive wire group 2 above the ground point in the high frequency band, a chiyoke coil 8 exhibiting an extremely high impedance in the radio frequency band is inserted into the pair of feeder lines. In addition, a large spring capacitor 9 is installed between the output line of the battery 3 and the ground point to prevent noise on the power supply line from entering the received signal.
is inserted.

As the heating conductive wire group 2, in addition to the pattern shown in FIG. 1, for example, a pattern in which the bus bars 5, 7 are connected and a current is passed between the bus bars 5, 7 and 6 can be used.

An antenna wire 10 is provided above the heating conductive wire group 2 . This antenna wire 10 includes a main antenna 11a consisting of three parallel lines connected in a substantially E-shape, and a connecting line 11 at the top of the main antenna.
Auxiliary antenna 11c connected via b, connected to the lower stage of the main antenna and heating conductive wire group 2
It consists of an auxiliary antenna 11d that is closely opposed to the auxiliary antenna 11c, and a folded portion 11e of the upper stage of the main antenna that has an element that is closely opposed to the auxiliary antenna 11c.
The dimensions of each part of this antenna wire 10 are a=b=
300 (mm), c=250, d=100, e=130, f=g
=h=i=20, j=15, k=5, and these dimensions and the main antenna 11 of the auxiliary antennas 11c and 11d are adjusted so that an almost circular omnidirectional characteristic can be obtained.
The connection position for a is determined.

In this embodiment, FM reception outputs are extracted from two different points on the antenna wire 10, and diversity reception is performed as described later. By obtaining outputs from two points having different phases with respect to the received radio waves induced in the antenna wire 10, it is possible to easily obtain received signals in which the angular positions of the dip points of the directivity characteristics are different from each other. Therefore, even if one reception output decreases at the dip point of the directional characteristic due to the direction (azimuth angle) of the car, it is possible to obtain a reception directional characteristic with less dip by performing diversity reception in which the reception output is switched to the other reception output. I can do it.

By the way, the inventor of this application has added an output circuit (feeder line and reception input circuit such as a preamplifier) to the above two points.
We focused on the fact that when the two received signals are connected to each other, the two received signals are affected by each other due to the grounding impedance (or input impedance) of the input point of the circuit, and the tuning state of their respective omnidirectional characteristics is disrupted. We considered deriving the received signal from a point where there is little mutual influence.

The diversity reception method and the method for selecting two antenna output points of this embodiment will be explained below.

In FIG. 1, the first feeding point 1 of the antenna wire 10
2 is provided at the upper folded portion of the main antenna 11a. Further, a second power supply point 14 (or 14') is provided at a position adjacent to this power supply point 12 (or on the opposite side of the window glass 1). The second feeding point 14 is connected to the middle or lower open end A or B of the E-shaped main antenna 11a or one open end C of the lower auxiliary antenna 11d as shown by the dotted line. Note that the feeding point 14' is connected to the center point D of the joint of three parallel lines forming the main antenna 11a.

The first and second feed points 12, 14 (or 1
4') are led out to a changeover switch circuit 17 via preamplifiers 13 and 15, respectively. The preamplifiers 13 and 15 may be narrowband tuned amplifiers,
Alternatively, a non-tuned amplifier may be used. switch circuit 1
In order to minimize the influence of periodic fluctuations in fading or multipath distortion, which occur as a reception point moves when a car is moving, on received sound quality, 7 is controlled by a control signal to be described later. It is switched to the side with better antenna output. The received signal selected by the switch circuit 17 is supplied to the FM receiver. Further, the AM reception output is led out from one feed point 14 to the preamplifier 16, and further
Sent to AM receiver.

Note that the gain of the preamplifiers 13 and 15 may be adjusted so that the two input levels of the switch circuit 17 are approximately equal, or the level of one received output may be adjusted with an attenuator before the input level of the switch circuit 17 is adjusted.
The signal may be supplied to the receiving circuit via a preamplifier.

Figures 2 a to c show the antenna wire 1 at the feed point 14.
Graphs showing the directivity characteristics of the outputs of feed points 12 and 14 when point A of 0 is connected (each
76MHz, 84MHz, 90MHz). Figure 2 a~
As shown in c, the outputs of the feed points 12 and 14 (solid line and dotted line) have almost the same reception level in each frequency range, and the angular positions of the dip points are different from each other. This is a received signal that can effectively perform diversity reception that mutually compensates for level drops.

However, in the case (condition) in which an output circuit (feeder line, preamplifier, etc.) is connected to both feed points 12 and 14, and in the case (condition) in which the output circuit is not connected to feed point 14, the conditions shown in Fig. 3 a to c. As shown in the directional characteristic graph of the feeding point 12, it was observed that the reception level and the directional characteristic changed significantly.
That is, the feed point 12 and the feed point 14 connected to point A
It is understood that these are terminal positions that influence each other when output circuits are connected to each other.

Other connection examples using the same method (feeding point 14 and point B or C, or feeding point 14' and point D)
As a result of investigating the mutual influence between the feed points 12 and 14 (or 14'), it was found that preferable results can be obtained when point C and the feed point 14 are connected.

FIGS. 4a to 4c are graphs showing the directivity characteristics of the outputs of the feed points 12 and 14 when point C of the antenna wire 10 is connected to the feed point 14, respectively. In this combination example as well, the outputs of the feeding points 12 and 14 have substantially the same reception level in each frequency range, as shown by solid lines and dotted lines, and the angular positions of the dip points are different from each other. Furthermore, when output circuits are connected to both feed points 12 and 14 (conditions)
In the case (condition) where no output circuit is connected to the feed point 14, there is no significant change in the reception level and directivity characteristics, as shown in the reception directional characteristic graphs of the feed point 12 shown in Figures 5a to 5c. I was able to confirm that there was no such thing. That is, the feed point 12 and the feed point 14 connected to the point C are output derivation positions that have little influence on each other when output circuits are connected to each other.

The reception outputs from the two signal derivation positions selected in this way are sent to the diversity reception circuit shown in FIG.

FIG. 6 is a block circuit diagram of an FM receiver used in the receiving system of this embodiment. 6th
In the figure, received signals obtained from feed points 12 and 14 are selected by a changeover switch circuit 17, also shown in FIG. 1, and supplied to a front end and IF circuit 24. This front end and IF
In circuit 24, tuning amplification, intermediate frequency conversion and
The received signal subjected to FM detection is supplied to a multiplexer 27 via a high-frequency cut control filter 25 and a noise blanker 26, where it is stereo demodulated and guided from the R channel and L channel output terminals to the audio power amplification section. be done. Note that the multiplexer 27 receives a stereo signal from the IF circuit 24.
A control signal c such as a monaural automatic switching signal is provided.

In the front end and IF circuit 24, detection of the received signal level (level detection of IF output or detection output) is performed in order to mute detuning noise between stations, and when the received signal level drops to a certain level, The detection output is muted. This received signal level detection signal a is IF
It is applied to a mute drive circuit in circuit 24 and to an automatic level setting circuit 28. This automatic level setting circuit 28 has a function of changing the threshold of the switching input level according to the switching frequency of the switch circuit 17, and generates a detection signal b when the switching input level is below this threshold. This detection signal b is sent to the antenna switching control circuit 30,
Here, a switching pulse d is generated in synchronization with the approximately 100 KHz clock output from the clock generator 29.
This switching pulse d is applied to the trigger input of the T-type flip-flop 31, thereby inverting the output (Q,) of the flip-flop 31.

The Q output and output of the flip-flop 31 are used as switching control signals for the switch circuit 17,
For example, when the received signal level at the feed point 12 falls below the set reference value, the flip-flop 31 is inverted and its Q output becomes a low level, and its output becomes a high level and the received signal level at the second feed point 14 is It can be switched to The output of the flip-flop 31 is also given to the automatic level setting circuit 28,
The operating mode of this circuit is switched so that it detects a drop in the reception level at feed point 14. Therefore, the next time the reception level at the feeding point 14 falls below the set reference level, the automatic level setting circuit 28 detects this, and the antenna switching control circuit 30 generates the switching pulse d again based on the detection output b. ,
The flip-flop 31 is inverted by this pulse d. Therefore, the switch circuit 17 is switched to the first feed point 12 side.

As a result, diversity reception is performed in which the antenna output is always switched to a higher antenna output than the set reception level.

Furthermore, in the embodiment shown in FIG. 6, variations in multipath distortion are detected and reception can be performed by switching to the reception output with less distortion. That is, the output of the front end and IF circuit 24 is
It is also supplied to a 19KHz bandpass filter 32, where the stereo pilot signal is extracted. This pilot signal is sent to the level fluctuation detection circuit 3.
given to 3. If the received signal is distorted by multipath, the pilot signal will also be distorted, so
By detecting the level variation (distortion component variation), it is possible to detect an increase or decrease in multipath distortion due to movement of the receiving point.

When the multipath distortion increases by a certain amount or more, the high frequency cut control filter 25 is operated with the output e of the level fluctuation detection circuit 33, and the high frequency distortion component of the detection output is cut and given to the multiplexer 27. At the same time, the output e of the level fluctuation detection circuit 33 is also sent to the antenna switching control circuit 30.
A switching pulse d is generated as described above and is switched to the other reception output in the same way as in the case of reception level fluctuations. As a result, a received signal with less multipath distortion can be obtained. Note that the antenna switching control circuit 30 forms a switching pulse d when either one of the outputs b and e of the automatic level setting circuit 28 and the level fluctuation detection circuit 33 is input. That is, the switching pulse d is created by the OR logic of the signals b and e. In addition, in order to prevent input switching due to reception level fluctuations during tuning, the reception level detection signal a obtained from the front end and IF circuit 24 is given to the antenna switching control circuit 28 as an operation prohibition signal. Therefore, the formation of the switching pulse d is prohibited in the weak electric field between stations during channel selection.

As described above, according to the present invention, two reception outputs are extracted from two different points on the antenna line, so that by selecting the position of each point, it is possible to determine the fluctuation state of the reception level and the angle of the dip point of the directivity characteristic. Reception outputs at different positions can be easily obtained. Therefore, even if there are fluctuations in the reception level due to movement of the reception point (fading, etc.) or changes in reception direction, it is possible to achieve diversity reception by selecting the better reception output. This can be carried out effectively, and therefore a high-quality received signal with reduced influence due to received level fluctuations can be obtained.

Furthermore, since the receiving characteristics of one signal derivation point do not change significantly depending on whether or not an output circuit is connected to the other signal derivation point, the respective signal derivation positions are selected, so good directivity characteristics can be obtained. The output circuit can be connected without disturbing the state in which the antenna wire is tuned so that a higher quality received signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front view of a rear window glass of an automobile showing one embodiment of the present invention and a circuit diagram of a receiving system, and FIGS. Graphs showing the reception directivity characteristics (76MHz, 84MHz, 90MHz) at points, Figures 3 a to b respectively show the mutual influence when the output circuit is connected to the two selected feeding points in the case of Figure 2. Directional characteristic graphs, Figures 4a to 4c are graphs similar to Figure 2 showing the directional characteristics at two other selected preferable feeding points of the antenna wire in Figure 1, and Figures 5a to c are graphs similar to Figure 2. A directional characteristic graph similar to FIG. 3 showing the mutual influence of the two feeding points in the case of FIG. 4, and FIG. 6 used in the receiving system of the present invention.
FIG. 2 is a circuit diagram of an FM receiver. In addition, in the symbols used in the drawings, 1...
...Rear window glass, 2... Heating conductive wire group, 10
...Antenna wire, 12, 14...Feeding point, 17
. . . changeover switch circuit, 28 . . . automatic level setting circuit, 31 . . . antenna switching control circuit.

Claims (1)

[Claims] 1. A group of heating conductive wires attached to the surface of the rear window glass of an automobile, an antenna wire attached to the upper or lower part of this group of heating conductive wires, and two mutually different points of this antenna wire. The first derived from
and a second output terminal, means for detecting the radio wave reception state of the first and second output terminals, and selecting an output from the first or second output terminal according to the output of the detection means. and a changeover switch means for receiving signals, and the receiving characteristics when the output circuit is connected to one of the first and second output terminals are different from those when the output circuit is connected to the other output terminal. A receiving device for an automobile, characterized in that the lead-out position of the other output terminal from the antenna wire is selected at a position that does not change significantly over time.