JP3002240B2 - Radio receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver, and more particularly to an improvement of a radio receiver suitable for use in a vehicle.

[Conventional technology]

In the radio receiver, when the level of the antenna reception signal decreases, the noise increases and the S / N decreases. Therefore, in order to prevent this S / N reduction, two filters of a wide frequency band (hereinafter, referred to as a wide filter) and a narrow frequency band (hereinafter, referred to as a narrow filter) are provided at an IF (intermediate frequency) stage. When the level of the antenna reception signal is high, the reception signal is output via the wide filter, and when the level of the antenna reception signal is reduced, the narrow filter is automatically or manually switched to improve the S / N. (For example, Japanese Utility Model Publication No. 59-6015).

[Problems to be solved by the invention]

By the way, in the conventional example described above, although effective for improving the S / N when the level of the antenna reception signal is reduced, the in-vehicle radio receiver receives a broadcast station and runs. If the broadcasting station is over-modulated or multi-path noise is generated in the state where the signal is present, a difference signal is generated due to a difference in gain and band characteristic between the wide-band and the narrow-band filters, and the switching operation may malfunction. There was a problem that it would occur.

Also, when the electric field strength of a broadcasting station adjacent to the frequency of the currently receiving broadcasting station is increased under a situation where the multipath noise is intense and inputted as a jamming wave to the currently received broadcasting, D / Because the U ratio fluctuates greatly,
There has been a problem that the wide filter and the narrow filter are frequently switched.

[Object of the invention]

The present invention is intended to solve the above-described problem. The purpose of the present invention is to automatically switch from a wide filter to a narrow filter when adjacent interfering radio waves arrive to prevent interference due to adjacent interfering radio waves. In addition, erroneous detection is reduced even if the currently receiving broadcasting station has overmodulation and multipath noise, and the hold time of the switch means becomes longer even if multipath noise occurs. Another object of the present invention is to provide a radio receiver in which the filter is not frequently switched.

[Summary of the Invention]

The radio receiver of the present invention is intended to achieve the above-mentioned object, and the output of the front end is divided into a wide filter and a narrow filter, and the output from each of the filters is detected. Demodulated by the
The difference between the demodulated outputs is subtracted by a subtractor, and when the result of the subtraction is larger than a predetermined value set by a comparator, it is determined that there is a jamming radio wave from an adjacent broadcasting station.
The switch means outputs the output from the narrow filter side to the multiplex at the subsequent stage, and changes the reference level of the comparator with the output from the S meter detector connected to the wide filter side, and the switch means When switching to the narrow filter side, over-modulation by not changing the reference level of the comparator, so that false detection due to multi-path noise is reduced,
The output from the S-meter detector is input to a waveform shaping circuit to extend the hold time of the switch means so that switching can be performed stably.

(Example of the invention)

Hereinafter, embodiments of a radio receiver according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment, wherein 1 is an antenna, 2 is a front end composed of a high-frequency amplification stage, a mixer and a local oscillation stage, selects and amplifies radio waves of a desired frequency, and Is attenuated and converted to an intermediate frequency. 3 is the front end 2
The intermediate frequency amplifying stage connected to the output is configured as follows. That is, the wide filter 3a ₁ and narrow filter 3a _2, the wide filter 3a _1, a detector 3b _1, 3b ₂ connected to the output of the narrow filter 3a _2,該検wave device 3b
A subtractor 3c for detecting a difference between outputs from ₁ , 3b _2;
a low-pass filter 3d (an active low-pass filter having a third-order maximum flat low-pass filter characteristic as shown in FIG. 3) for removing noise and a modulation signal contained in the output of c; A comparator 3e for sending an output when the output from the filter 3d is larger than a predetermined value; and the detector 3
Switch means 3f for selecting the output from 3b ₁ or 3b ₂ and sending it to the subsequent multiplex 4 and detector 3b ₁ on the wide filter 3a ₁ side, which include overmodulation and multipath noise. The comparator 3e.
And the switch means 3f
Is switched to the narrow filter 3a ₂ side,
An S-meter detector 3g that operates so as not to change the reference level of the comparator 3e.

Reference numeral 4 denotes a multiplex for converting an audio signal detected by the detectors 3b ₁ and 3b ₂ selected by the switch means 3f into a stereo signal.

Next, to explain the operation based on the above configuration, the FM radio wave from the broadcasting station input from the antenna 1 is amplified and output after the radio wave of the desired frequency is selected in the front end 2.

And the FM signal of the selected broadcasting station is a wide filter
3a ₁ through the input to the detector 3b _1, or, is input to the detector 3b ₂ via the narrow filter 3a _2. Then, the FM signals from the respective filters 3a ₁ and 3a ₂ are demodulated in the detectors 3b ₁ and 3b ₂ and input to the subtractor 3c.

Here, when there is no adjacent broadcast stations broadcast frequency are close, the output signal level than the wide filter 3a ₁ and narrow filter 3a ₂ is a substantially identical output than the subtracter 3c is small, therefore, the comparator 3e No output is sent out, and the switch means 3f is switched to the detector 3b ₁ side, and the detector 3b ₁
Is output to the multiplex 4.

On the other hand, when there is an adjacent broadcast station having a close broadcast frequency, the detector 3 output via the wide filter 3a ₁
The output than b ₁ but signal from an adjacent broadcast stations as shown in the FIG. 2 (a) is superimposed, the the output of from detector 3b ₂ output through the narrow filter 3a ₂ As shown in FIG. 2 (b), signals from adjacent broadcasting stations are not superimposed. Therefore, when the outputs from the detectors 3b ₁ and 3b ₂ are subtracted by the subtractor 3c, the output of the difference is sent out.This output is compared with the reference value in the comparator 3e, and is compared with the reference value. subtractor output from the comparator 3e and output from 3c is large is sent, the switching means 3f is switched to the narrow filter 3a ₂ side. Accordingly, the signal output through the narrow filter 3a ₂ and detector 3b ₂ is input to the multiplex 4, radio waves from the adjacent broadcasting station receives only broadcast from a broadcasting station desired are removed It can be heard.

In the present embodiment, was connected to the low-pass filter 3d downstream of the subtracter 3c is characteristic difference between the wide filter 3a ₁ and narrow filter 3a ₂ is intact, the difference detector 3b ₁ and detector 3b ₂ Appears, and even if there is no jamming radio wave from an adjacent broadcast station, the detector
Since the output difference between 3b ₁ and detector 3b ₂ is generated and there is a risk of erroneous detection, the output from subtractor 3c is
Passing through 3d removes noise and modulated signals. Therefore, it is possible to determine whether there is a radio wave from an adjacent broadcast station based on the output level of the low-pass filter 3d.
The sound of the interfering station can be heard in the audio band, the broadcast energy is generally 1 KHz or less, and even if the signal passes through the low-pass filter 3d, the adjacent station can be detected. The difference in the characteristics of the wide filter 3a ₁ and narrow filter 3a ₂ is ,, in particular,
This is remarkable in the high frequency range of the audio signal, the effect is very small, and erroneous detection is reduced.

If multipath noise is included in the output from the detector 3b ₁ or the currently received broadcast is overmodulated, a low output is sent from the S-meter detector 3g and the comparator Since the reference level of 3e is lowered, malfunction due to overmodulation and multipath noise is prevented.
Further, even when the overmodulation and multipath noise occurs, when the switch means 3f is switched narrow filter 3a ₂ side, lowering the reference level to the S meter detector 3g comparators 3f Does not send any output
The interference detection capability is not significantly impaired.

Next, a second embodiment of FIG. 4 will be described. This embodiment is different from the first embodiment in that a comparator
A waveform shaping circuit 3h such as a one-shot multivibrator is connected between 3e and the switch means 3f, and an S meter detector 3g is connected.
The only difference is that the output from the switch 3f is not fed back to the S-meter detector 3g.

Next, in explaining the operation of this embodiment, the inclusion of multipath noise in the output than similarly detectors 3b ₁ and described above, sharply lower from the S meter detector 3g is sent Lowers the reference level of the comparator 3e.
Malfunction due to multipath noise is prevented. Also, S
Since the output from the meter detector 3g is also input to the waveform shaping circuit 3h, the recovery time becomes longer than usual, the hold time of the switch means 3f becomes longer, and the switch means 3f is frequently switched. It is stable without any.

〔The invention's effect〕

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 of the filters with a detector, and subtracts the difference between the modulated outputs with a subtractor. When the result of the subtraction reaches or exceeds a level set in advance by the comparator, it is determined that there is an interfering radio wave from an adjacent broadcasting station, and the switch means outputs the output from the narrow filter side to the subsequent multiplex. As a result, the in-vehicle radio receiver is made difficult to hear due to interference, the reference level of the comparator is changed by the output from the S-meter detector connected to the wide filter side, and the switch means is provided with a narrow filter. Side, the reference level of the comparator is not changed so as to prevent over-modulation and erroneous detection due to multipath noise. In addition, since the output from the S-meter detector is input to the waveform shaping circuit to extend the hold time of the switch means, the switching means can be switched stably. It is.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram showing a detector output of the above, FIG. 3 is a circuit diagram of a low-pass filter of the above, and FIG. It is a block diagram showing other examples. 2 ... front end, 3 ... intermediate frequency amplification stage, 3a ₁ ...
… Wide filter, 3a ₂ … Narrow filter, 3b ₁ , 3b ₂ …
… Detector, 3c …… Subtractor, 3d …… Low-pass filter, 3e
... Comparator, 3f switch means, 3g S-meter detector, 3h waveform shaping circuit, 4 multiplex.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/06-1/28

Claims (2)

(57) [Claims] In an intermediate frequency amplification stage connected between a front end and a multiplex, a wide filter and a narrow filter to which an output from the front end is input, and an output from the filter connected to each of the filters. A detector for demodulating, a subtractor for obtaining a difference between outputs from the detector, a comparator for transmitting an output when an output from the subtractor becomes equal to or higher than a preset reference level, and Switch means for outputting a signal from a detector connected to the narrow filter side to the multiplex according to the output of the narrow filter, and detecting an S-meter output from the wide filter system, and the S-meter output sharply decreases. S that varies the comparison level of the comparator when
A radio receiver comprising a meter detector, wherein when the switch means is connected to the narrow filter side, the comparison level of the comparator is not changed. 2. An intermediate frequency amplifying stage connected between a front end and a multiplex, wherein a wide filter and a narrow filter to which an output from the front end is input, and an output from the filter connected to each of the filters. A detector for demodulating, a subtractor for obtaining a difference between outputs from the detector, a comparator for transmitting an output when an output from the subtractor becomes equal to or higher than a preset reference level, and Switch means for outputting a signal from a detector connected to the narrow filter side to the multiplex according to the output of the narrow filter, and detecting an S-meter output from the wide filter system, and the S-meter output sharply decreases. S that varies the comparison level of the comparator when
A meter detector, and a waveform shaping circuit such as a one-shot multivibrator for extending a hold time after a switch of the switch means is switched over when an S-meter output from the S-meter detector is lowered. A radio receiver, characterized in that: