JPS5810932A - Electronic tuning type car radio for discrimination of content - Google Patents

Abstract

PURPOSE:To decrease multipath nosise without accompaning switching noise at diversity reception, by taking a reception system including an antenna as two systems, through the suitable automatic channel selection of the same program broadcast. CONSTITUTION:Two systems are constituted with high frequency circuits 15a and 15b, intermediate frequency circuits 16a and 16b, FM detection circuits 17a and 17b, and stereo demodulation circuits 18a and 18b, in which the reception system is connected to antennas 11 and 12, respectively. A reception level discriminating circuit 7, a broadcast content detecting circuit 8 and a noise detecting circuit 14 are connected between the circuits 16a, 16b and the 17a, 17b, respectively. The output of the circuits 7, 8 and 14 is applied to a signal processing circuit controlling local oscillation circuits 20a and 20b. If the level of a broadcast receiving at one reception system is decreased, the automatic channel selection of the other reception system is performed with the control of the circuit 9, allowing to switch the diversity reception without switching noise.

Description

[Detailed Description of the Invention] This invention relates to improving the reception performance of an FM electronically tuned car radio, which is equipped with a noise reduction function using FM multipath and an automatic tuning function for broadcasting stations with the same program. It concerns car radios.

Regarding reception conditions on conventional car radios, the service area for decoy broadcasts is generally relatively narrow, with a radius of about 50 to 10G. It is necessary to perform a channel selection operation each time in the boundary area, which poses problems in terms of safe driving and the cumbersome operation of the radio. In addition, since fermentation transmission uses a frequency with a wavelength of around 3 m, direct waves and reflected waves from broadcasting stations interfere with each other, causing noise due to fluctuations in the received electric field level ν while driving and noise due to so-called machining path distortion. The reception conditions of in-vehicle car radios were not always satisfactory.

Figure 1 shows an example of a conventional technique used to automatically receive broadcast stations with the same broadcast content whenever driving across service area boundaries. In Figure 1, θ) is the antenna, @ is the High frequency circuit, (powder is intermediate frequency circuit, (41 is FM detection circuit, (51 is stereo demodulation circuit, (6) is local oscillation circuit, (7) is reception level judgment circuit, 1lkl is broadcast content detection circuit, 19) is a signal processing circuit port α is a memory.Next, the operation will be explained.In order to always receive broadcasting stations with the same broadcast contents while the car is running, the receiving station (hereinafter the receiving station [F ]), it is necessary to select a receivable broadcasting station at level p, and to determine whether the broadcast content of that broadcasting station 1 is the same as that of the station 0 currently being received. In order to achieve this with the receiving circuit of the system, it is necessary to momentarily interrupt the reception of the station [F] that is currently being received, and during this time to select the broadcasting station and determine the broadcast content.

One possible way to prevent the user from perceiving the momentary interruption of station 0 during reception is to use the time when the sound of the broadcast content ends. Broadcast content detection circuit (
Step 8) first detects a break in the broadcast content of station 0 that is being received. Based on this information, the signal processing circuit 19) puts the electronically variable local oscillation circuit (61) into a search state.

If a receivable station is found by the reception level determination circuit (7), the broadcast content of that station is detected by the broadcast content detection circuit (8). One way to determine whether the broadcast content is the same as that of the receiving station [F] is to check whether the sound trail is cut off. This method determines the identity of two broadcast contents in which the sound trail is cut off several times. Based on the signal from the broadcast content detection circuit (8), the signal processing circuit (9)
) determines that it is the same as receiving station 0, data corresponding to the frequency of this station is stored in the memory Itω. Furthermore, if there is a receivable station, the same process is repeated and the frequency of the station with the same broadcast content is stored in the memory IO1.

The car enters the border area of the service area and the station receiving [
When the reception condition of [F] deteriorates, other receivable stations with the same broadcast content stored in the memo tnω are automatically selected.

In the above-mentioned conventional technology, since the sameness of broadcast content is determined by one system of receiving circuits, it is necessary to restrict the use of the sound trail cut-off time of the broadcast content in order to reduce the deterioration of the quality of the broadcast content. Therefore, there are problems such as the time required to determine the identity of the broadcast contents and the time required to determine the identity greatly depending on the broadcast contents. Therefore, even if the reception condition of the receiving station [F] deteriorates, there is a drawback that it may not be possible to shift to a station with a better reception condition. Furthermore, since the audio output is muted when the sound trail ends, there is no noise during this time, resulting in an unnatural feeling.

Another problem when receiving FM broadcasts in a car is noise caused by the multi-bass phenomenon of broadcast waves. An example of a conventional technique for reducing this noise is shown in Fig. 2. In Fig. 2, (+1) is antenna A, (121 is antenna B).
, 03 is an antenna switching circuit, and 04 is a noise detection circuit.

FIG. 2 shows what is known as the so-called pre-detection dipercity reception system in which two antennas are connected to one reception system. The two antennas are designed to receive received signals with as little correlation as possible to each other in terms of noise, and an example is the so-called space diversity method, in which the antennas are spaced apart spatially by at least 1/4 wavelength of the received carrier frequency. It is well known as The reception level judgment circuit (7) and the noise detection circuit 04 compare the reception level and the noise level with a certain reference setting level, and cause the signal processing circuit (91) to determine whether to switch the antenna. With this method, it is possible to reduce multipath noise compared to when receiving with one antenna.

In the conventional technology described above, since two antennas are switched in one receiving system, it is necessary to set a certain reference level μ regarding the reception level and noise level, and the disadvantage is that noise caused by this level setting remains. It was small. Furthermore, switching the antenna at the high frequency stage causes discontinuity of the carrier signal, which also has the disadvantage of generating noise during switching when irM detection is performed.

This invention was made in order to eliminate the drawbacks of the conventional system as described above, and by providing two receiving systems, it is possible to properly perform automatic tuning of broadcast stations with the same program.
The present invention provides a car radio that can more effectively reduce FM multipath noise.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure (ol, (121 are antennas A and B).

(15m), (Nib) are high frequency circuits A, B, (
16a), (16b) are intermediate frequency circuits A, B, (
17m), (17b) are FM detection circuits A, B, (
181) and (18b) are stereo demodulation circuits A.

B, (111 is an audio signal switching circuit, (20ri,
(20b) are local oscillation circuits A and B.

First, automatic tuning of broadcast stations with the same program will be explained. By having two receiving systems connected to antenna A (Il+ and antenna B1121), it is possible to receive station 0 on one receiving system while receiving it at an appropriate timing using the other receiving system. This makes it possible to select a station and determine the content of the broadcast.Discrimination of the broadcast content is performed by the broadcast content detection circuit (8), but instead of using the sameness of sound traces that was done with the conventional technology. By using one frequency spectrum, amplitude, cross-correlation coefficient, etc., it is possible to eliminate the conventional drawback that the chance of identity determination is limited by the broadcast content. can always be stored in the memory as the latest information, and if the receiving condition of station 0 that is currently receiving deteriorates, automatic switching to another station with the same program can be performed immediately.

Next, reduction of noise caused by multipath phenomenon will be explained. From antenna A (11) to stereo demodulation circuit A C
An audio signal switching circuit (I@
to reduce noise associated with multipath phenomena. The reception system with the best reception state is selected by comparing the reception conditions of the two systems at appropriate timing with a reception level judgment circuit (11) and a noise detection circuit (14). The drawbacks of the switching method can be eliminated.

In addition, in the above embodiment, the receiving system that performs the frequency search for automatic tuning of the same program broadcast is not specified in particular, but it may be limited to one of the two receiving systems, or , the frequency search may be performed by switching each time to a receiving system that does not output an audio signal due to diversity reception.

Furthermore, although the above embodiment has been described using two independent antennas in appearance, an antenna system having two feeding points that can be electrically considered as two antennas may be used.

As described above, according to the present invention, by providing two receiving systems, it is possible to appropriately perform automatic tuning of the same program broadcast, and without causing switching noise during diversity reception. This has the effect of reducing chime noise. Furthermore, since the two receiving systems have the two functions of automatic tuning of the same program broadcast and diversity reception, there is an effect that the performance and cost can be satisfied.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional car radio that automatically selects channels for broadcasting the same program, Fig. 2 is a block diagram of a conventional car radio that receives diversity before detection, and Fig. 3 is a block diagram of a conventional car radio that receives diversity before detection. FIG. 3 is a diagram showing a block diagram of a car fujio according to an embodiment. In the figure, (ft...reception level judgment circuit% (8)...
...Broadcast content detection circuit, 1llll...Antenna system...Antenna B, (14...Noise detection circuit,
(15m), (15b)...High frequency circuit A, B
, (lem), (lsb) - intermediate frequency circuit A, B
. (17m), (1?b)...FM detection circuit A,
B, (18a), (18b)... Stereo demodulation circuits A, B, 1lSI... Audio signal switching circuits. Note that in FIG. 1, the same reference numerals indicate the same or phase j portions. Agent Makoto Kuzuno - Figure 1 Figure 2

Claims (1)

[Scope of Claims] 0) An antenna system having two antennas provided for diversity reception or two feeding points that can be electrically considered as two antennas, and two high frequency circuits respectively connected to the antennas. , two intermediate frequency circuits connected to each of these two high frequency circuits, two FM detection circuits connected to each of these two intermediate frequency circuits, and a stereo demodulation circuit connected to these two FM detection circuits. The device is characterized by comprising a circuit, an audio signal switching circuit, a reception level determination circuit, a noise detection circuit, and a broadcast content detection circuit, and is capable of automatically selecting broadcast stations with the same broadcast content at the same time as performing diversity reception. Content-discriminating electronically tuned car radio. The content-discriminating electronic tuning type car according to claim 1, characterized in that the frequency search performed for automatically selecting broadcast stations with the same broadcast content as described in @g is specified to one of the reception systems. radio. (3) The first aspect of the present invention is characterized in that the frequency search performed in order to automatically select a broadcasting station with the same broadcast content as described above is performed by switching to a receiving system 'to which no audio signal is output each time'. Content-discriminating electronically tuned car radio as described in the section.