JPH0433420A - Radio receiver - Google Patents

Abstract

PURPOSE:To prevent a crosstalk due to an adjacent station interference radio wave by changing over forcibly a switch to the position of a narrow filter when an electric field strength from a broadcast station is decreased. CONSTITUTION:When an electric field strength from a broadcast station is decreased, since an output from a detector 3b1 is decreased, its output as a mean electric field level is compared with a reference value of a comparator 3g2 at the comparator 3g2, and when an output from the detector 3b1 is smaller than a reference value, a high level output is sent from the comparator 3g2. The output of an OR circuit 3f1 is always at a high level by the high level output independently of the output from the comparator, the output of an inverter goes to a low level, an analog switch 3f3 is opened and an analog switch 3f4 is closed. Thus, a radio wave from an adjacent station is eliminated and only the broadcast from a desired broadcast station is received.

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 received signal to be tested drops, it is difficult to use the in-vehicle radio receiver to receive a certain broadcast station while driving. When the electric field strength of a broadcasting station adjacent to the frequency of the broadcasting station becomes strong, it is input as an interference radio wave to the broadcast currently being received, causing interference. In addition, even if there are no adjacent broadcast stations, if the electric field strength of the broadcast station you are currently listening to becomes weaker or stronger, the wide filter will frequently switch from the wide filter to the narrow filter, or vice versa. The problem was that it became difficult.

[Purpose of the invention]

The present invention is intended to solve the above-mentioned problems, and its purpose is to automatically switch from a wide filter to a narrow filter when adjacent interference waves arrive to prevent interference caused by adjacent interference waves. and also,
To provide a radio receiver that automatically fixes to the narrow filter side when the electric field strength of the broadcasting station being listened to becomes weak, thereby preventing frequent switching between the wide filter and the wide filter. be.

[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 if the subtracted result is larger than a predetermined value by a comparator, the signal from the adjacent broadcasting station is Assuming that interference radio waves exist, the switch means is configured to output the output from the narrow filter side to the subsequent multiplex, and when the electric field strength from the broadcasting station decreases, it is forcibly switched to the narrow filter side. This is to make it fixed.

[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. Reference numeral 3 denotes an intermediate frequency amplification stage connected to the output of the front end 2, which is constructed as follows. That is, a wide filter 3as, a narrow filter 3ax, and detectors 3b1 and 3 connected to the outputs of the wide filter 3a1 and the narrow filter 3a2.
bz, a subtracter 3c that detects the difference between the outputs from the detectors 3bl and 3b2, and a low-pass filter 3d (that removes noise and modulation signals contained in the output of the subtracter 3C).
An active low-pass filter (as shown in FIG. 3, which has a third-order maximum flatness low-pass filter characteristic) and a comparator that sends an output when the output from the low-pass filter 3d is larger than a predetermined value. 3e, and the output from the detector 3bs or 3b2 is selected based on the output from the comparator 3e, and the output from the multiplexer 4 at the subsequent stage is selected.
and a switch means 3f which switches to the detector 3b2 side when the output from the signal level detecting means 3g which will be described later is input, and a switch means 3f which switches the output to the detector 3b2 side when the output from the detector 3b1 becomes smaller than a preset value. The signal level detection means 3g as shown in FIG.

A multiplexer 4 converts the audio signal passed through the switch means 3r described above into a stereo signal.

Here, to explain the signal level detection means 3g shown in FIG. 4, a comparator 3g2 inputted through a low-pass filter 3g1 consisting of a resistor R and a capacitor C is compared with a preset reference voltage, and the It is configured to send an output if the result of the comparison is lower than the reference voltage.

Furthermore, to explain the switch means 3f in FIG.
The output from the comparator 3e described above is input to the OR circuit 3fx, and the output from the signal level detection means 3g is also input to the OR circuit 3fx.
is input. The output of this OR circuit 3fi is connected to an analog switch 3fs through an inverter 3f2, and directly to an analog switch 3fa.

The operation of this switch means 3f is as follows.

When the electric field strength from the broadcasting station currently being received decreases, the output from the detector 3bs decreases, so the output becomes the average electric field level by the comparator 3gz and is compared with the reference value of the comparator 3g2. , when the output from the detector 3b1 is smaller than the reference value, a high level output is sent from the comparator 3g2. Due to this high level output, the output of the OR circuit 3f1 is always at a high level regardless of the output of the comparator, the output of the inverter 3fz is at a low level, the analog switch 3fs is turned off, and the analog switch 3f4 is turned on.

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 3bs via the wide filter 3a1, or input to the detector 3b2 via the narrow filter 3a2.

The FM signals from the respective filters 3a1y3a2 are demodulated by the detectors 3bt and 3b2, and then sent to the subtracter 3C.
is input.

Here, if there is no adjacent broadcasting station whose broadcast frequency is close to each other, the output signal level from the wide filter 3a1 and the narrow filter 3a2 is between -, so the output from the subtracter 3C is small, and therefore The output becomes low level. On the other hand, when the electric field strength of the receiving broadcasting station is strong enough, the output from the signal level detection means is low level, so both inputs of OR circuit 3 "1" become low level, and the analog switch 3fs On, the analog switch 3f4 turns off, and the signal from the detector 3b1 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 3b1 that is outputted via the wide filter 3a1 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 3bs 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 of the detector 3b1 and the detector 3b2 are subtracted by the subtracter 3C, the difference output is sent out.This output is compared with a reference value in the comparator 3e, and from the reference value, the subtracter 3C sends out the difference output. If the output from 3c is large, comparator 3e
Since the output becomes a high level, the output level of the OR circuit 3f1, which is related to the output level of the signal level detection means 3g, becomes a high level, the analog switch 3fa turns off, the analog switch 3f4 turns on, and the detector 3
The signal from b2 is output to multiplex 4. As a result, the signal output via the narrow filter 3a2 and the detector 3b2 is input to the multiplex 4, so radio waves from adjacent broadcasting stations are removed and only broadcasts from the desired broadcasting station can be received and listened to. It is something.

In this embodiment, the low-pass filter 3d is connected after the subtracter 3C because the difference in characteristics between the wide filter 3a1 and the narrow filter 3a2 is directly expressed as the difference between the detector 3b1 and the detector 3bt. Therefore, even if there is no interfering radio waves from an adjacent broadcasting station, the output from the subtracter 3c may be different due to noise or modulated signals, which may cause a difference in the output between the detectors 3b1 and 3b1, resulting in false detection. By passing the signal through the low-pass filter 3d, noise and modulation signals are removed. Therefore, it can be determined whether or not there is a radio wave from an adjacent broadcasting station based on the output level of the low-pass filter 3d.In other words, if interference is received from an adjacent broadcasting station, the sound of the interfering station will be heard in the audio band. , and the broadcast energy is generally IK
Hz or less, and adjacent stations can be detected even if the signal passes through the low-pass filter 3d. Further, the difference in characteristics between the wide filter 3a1 and the narrow filter 3a2 is 1, which is particularly noticeable in the high frequency range of the audio signal, and the influence thereof is extremely small, resulting in fewer false detections.

〔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 subtraction result reaches a level set in advance by the comparator, it is determined that there is interference from an adjacent broadcasting station, and the switch means is configured to output the output from the narrow filter side to the subsequent multiplex. As a result, it can be used as an in-vehicle radio receiver to eliminate the difficulty of listening due to interference, and when the electric field strength of the broadcasting station you are listening to becomes weak, the switch means multi-channels the signal sent out via the narrow filter side. Since the signal is output to the Plex, it is possible to listen to broadcasts with good sensitivity and less noise.

[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 above detector, Fig. 3 is a circuit diagram of the low-pass filter shown above, and Fig. 4 is a diagram of the signal level detection means. Circuit Diagram FIG. 5 is a circuit diagram of the switch means. 2...Front end, 3...Intermediate frequency amplification stage, 3
a1...Wide filter, 3a2...Narrow filter, 3tz, 3b2...Detector, 3c...Subtractor,
3d...Low pass filter, 3e...Comparator, 3f
...Switch means, 3g...Signal level detection means,
4...Multiplex.

Claims (1)

[Claims] 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 an output from the filter connected to each filter. a subtracter that obtains the difference between the outputs from the detector, a comparator that sends out an output when the output from the subtracter exceeds a preset reference level, and the comparator. switch means for outputting a signal from a detector connected to the narrow filter side to the multiplex by an output from the detector; A radio receiver comprising: signal level detection means for transmitting an output that switches the switch means to a narrow filter side when detected.