JPH0433422A - Radio receiver - Google Patents

Abstract

PURPOSE:To prevent a crosstalk due to an adjacent station disturbing radio wave by outputting a signal from a detector connected to a narrow filter to a multiplexer when an output from a subtractor reaches a preset output or above. CONSTITUTION:When outputs from detectors 3b1, 3b2 are subtracted at a subtractor 3c, since the difference output is sent, the output is compared with a reference value at a comparator 3d, and when the output from the subtractor 3c is larger than the reference value, an output is sent from the comparator 3d and a switching means 3e is changed over to the position of a narrow filter 3a2. Then a signal outputted through the narrow filter 3a2, the detector 3b1 is inputted to a multiplexer 4. Thus, a radio wave from an adjacent station is eliminated and only a broadcast from a desired broadcast station is received and listened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio receiver, and particularly to an improvement in a radio receiver suitable for use in a vehicle.

[Conventional technology]

In a radio receiver, when the level of a signal received by an antenna decreases, noise increases and the S/N ratio decreases. Therefore, this S/N
In order to prevent a drop in the antenna reception signal, two filters, a wide frequency band filter (hereinafter referred to as wide filter) and a narrow frequency band filter (hereinafter referred to as narrow filter), are connected to the IF (intermediate frequency) stage. When the level of the antenna reception signal is high, the received signal is output through the wide filter, and when the level of the above-mentioned antenna reception signal decreases, it is automatically or manually switched to the narrow filter.
were trying to improve N (for example,
Publication No.).

[Problem to be solved by the invention]

By the way, in the conventional example described above, although it is effective in improving the S/N when the level of the antenna reception signal decreases, the in-vehicle radio receiver does not receive a certain broadcast station while driving. If the electric field strength of a broadcasting station adjacent to the frequency of the broadcasting station becomes strong, it will be input as interference radio waves to the broadcast currently being received, causing interference.

[Purpose of the invention]

The present invention is intended to solve the above-mentioned problems, and its purpose is to automatically switch from the wide filter to the narrow filter when adjacent jamming waves arrive to prevent interference caused by adjacent jamming waves. We do not provide any radio receivers for you.

[Summary of the invention]

The radio receiver of the present invention is intended to achieve the above-mentioned object, and its gist is to distribute the output from the front end to a wide filter and a narrow filter,
The output from each of the filters is demodulated by a detector, the difference between the demodulated outputs is subtracted by a subtracter, and when the subtracted result reaches a certain level or more, it is determined that there is interference from an adjacent broadcasting station. As a result, the switching means is configured to output the output from the narrow filter side to the subsequent multiplex, and a delay circuit is connected between the detector connected to the wide filter and the subtracter to eliminate the delay caused by the narrow filter. In addition, a low-pass filter is connected between the subtracter and the switch means to match the difference in time.

[Embodiments of the invention]

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

FIG. 1 shows a block diagram of the first embodiment, in which 1 is an antenna, 2 is a front end consisting of a high frequency amplification stage, a mixer, and a local oscillation stage, which selects and amplifies radio waves of a desired frequency, and It attenuates other signals and converts them to intermediate frequencies. 3 is a wide filter 3a1 and a narrow filter 3a2 connected to the output of the front end 2, detectors 3bz and 3b2 connected to the outputs of the wide filter 3a1 and narrow filter 3a2, and the detector 3bt*3b2. A subtracter 3C that detects the difference in output, a comparator 3d that sends out an output when the output from the subtracter 3C is larger than a predetermined value, and the detector 3bx or 3b2 according to the output from the comparator 3d. an intermediate frequency amplification stage 4 comprising a switch means 3e for selecting an output from the output and sending it to a subsequent multiplex 4;
is a multiplex that converts the audio signal detected by the detector 3b1t3b2 selected by the switch means 3e into a stereo signal.

Next, the operation will be described based on the above-described configuration. FM radio waves from a broadcasting station inputted from the antenna 1 are amplified and outputted after a radio wave of a desired frequency is selected in the front end 2.

Then, the FM signal of the selected broadcasting station is input to the detector 3bt via the wide filter 3a1, or input to the detector 3b2 via the narrow filter 3a2.

The FM signals from the respective filters 3a1 and 3a2 are demodulated by the detectors 3b1 and 3b2, and then sent to the subtracter 3C.
is input.

Here, if there is no adjacent broadcasting station whose broadcasting frequency is close to each other, the output signal level from the wide filter 3at and the narrow filter 3a2 is between -, so the output from the subtractor 3c is small, and therefore No output is sent out, the switch means 3e is switched to the detector abs side, and the signal from the detector 3bt is output to the multiplex 4.

On the other hand, if there is an adjacent broadcasting station whose broadcasting frequency is close to each other, the output from the detector 3bx that is outputted via the wide filter 3as has a signal from the adjacent broadcasting station as shown in (a) of FIG. Although the signals are superimposed, the narrow filter 3a
The output from the detector 3b1 which is output via the second
As shown in (b) of the figure, signals from adjacent broadcasting stations are not superimposed. Therefore, when the outputs from the detector 3bs and the detector 3bt are subtracted by the subtracter 30''?, the difference output is sent out.This output is compared with the reference value in the comparator 3d, and the reference value is When the output from the subtractor 3c is larger, the output is sent from the comparator 3d, and the switch means 3e is switched to the narrow filter 3a2 side.Thereby, the signal outputted via the narrow filter 3a2 and the detector 3b1 is Since the signal is input to the Plex 4, radio waves from adjacent broadcasting stations are removed and only the broadcasting from the desired broadcasting station can be received and listened to.

Next, the second embodiment shown in FIG. 3 will be explained. In this embodiment, the detector 3 in the embodiment shown in FIG.
The only difference is that a delay circuit 3f consisting of a capacitor and a resistor is connected between b1 and the subtracter 3c.

In the embodiment shown in FIG. 1, since the delay time in the narrow filter 3a2 is larger than that in the wide filter 3a1, there is a problem that the difference in delay time affects even after detection, making it impossible to sufficiently cancel the modulation component of the desired broadcasting station. A point occurs. Therefore, in the present embodiment, the signal outputted from the detector 3b1 via the wide filter 3a1 is delayed by the delay circuit 3f so that the phase is approximately the same as that of the signal from the narrow filter 3a2. The influence of the difference in delay time between the wide filter 3at and the narrow filter 3a2 is reduced, and the amount of cancellation of modulation components is increased (and false detections are reduced).

Next, the third embodiment shown in FIG. 4 will be explained. In this embodiment, the subtracter 3 in the embodiment shown in FIG.
The only difference is that a low-pass filter (an active low-pass filter having a third-order maximum flatness low-pass filter characteristic) 3g shown in FIG. 5 is connected between C and the comparator 3d.

In the embodiment of FIG. 1, the difference in characteristics between the wide filter 3a1 and the narrow filter 3a2 is directly applied to the detector 3
bs and the detector 3bt, and even if there is no interfering radio waves from an adjacent broadcasting station, the difference in output between the detector 3bs and the detector 3bs due to noise or modulated signals may result in false detection. A problem occurs. Therefore, in this embodiment, noise and modulation signals are removed by passing the output from the subtracter 3c through a low-pass filter 3g. Based on the output level of the low-pass filter 3g, it can be determined whether or not there is a radio wave from an adjacent broadcasting station. In other words, when a jamming signal is received from an adjacent broadcasting station, the sound of the interfering station can be heard in the audio band, and the broadcasting energy is generally below IKHz, so the adjacent station cannot be detected even if it passes through the low-pass filter 3g. can. Also,
The difference in characteristics between the wide filter 3a1 and the narrow filter 3ax is 1, which is particularly noticeable in the high frequency range of the audio signal, and in the circuit of this embodiment described above, this effect is extremely small and false detections are reduced. It is something.

〔Effect of the invention〕

As described above, the present invention distributes the output from the front end to a wide filter and a narrow filter, demodulates the output from each filter using a detector, and subtracts the difference between the demodulated outputs using a subtracter. When the result of the subtraction reaches a certain level, it is assumed that there is interference from an adjacent broadcasting station, and the switch means outputs the output from the narrow filter side to the multiplex at the subsequent stage. In addition, a delay circuit is connected between the detector connected to the wide filter and the subtracter to compensate for the difference in delay time caused by the narrow filter. Further, a low-pass filter is connected between the subtracter and the switch means to prevent false detection due to noise or modulated signals, and to prevent the false detection when there is no interfering radio wave from an adjacent broadcasting station. This has the effect that switching of the switching means does not occur.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing the output of the same detector as above, Fig. 3 is a block diagram showing a second embodiment, and Fig. 4 is a block diagram showing the output of the same detector. FIG. 5 is a circuit diagram of the same low-pass filter as described above. 2...Front end, 3...Intermediate frequency amplification stage, 3
a1...Wide filter, 3az...Narrow filter, 3b1, 3b2...Detector, 3C...Subtractor,
3d... Comparator, 3e... Switch means, 3f...
・Delay circuit, 3g...Low pass filter, 4...Multiplex circuit. Patent applicant Pioneer Corporation

Claims (3)

[Claims] (1) In the intermediate frequency amplification stage connected between the front end and the multiplex, there are a wide filter and a narrow filter into which the output from the front end is input, and a wide filter and a narrow filter that are connected to each filter and demodulate the output from the filter. a detector, a subtracter that obtains the difference between the outputs of the detector, and a signal from the detector connected to the narrow filter when the output from the subtracter exceeds a preset output; 1. A radio receiver comprising switch means for outputting to a multiplex. (2) The radio receiver according to claim 1, further comprising a delay circuit connected between the detector connected to the wide filter side and the subtracter. (3) The radio receiver according to claim 1, further comprising a low-pass filter connected between the subtracter and the switch means.