JP3119490B2 - Diversity type FM receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting multipath interference in a diversity type FM multiplex broadcasting receiver, and more particularly to a diversity type method for selectively controlling an antenna from among a plurality of antennas, from which a received signal with less interference is obtained. The present invention relates to an FM receiver.

[0002]

2. Description of the Related Art It is difficult for an on-vehicle FM receiver to always receive FM broadcasts in a stable state due to multipath interference or the like. Therefore, a spatial diversity system has recently been adopted in a vehicle-mounted FM receiver in order to improve reception quality.

FIG. 1 shows the configuration of a conventional FM multiplex broadcasting receiver of this type, wherein reference numerals 1 and 2 denote A and B channels,
1, 21 are antennas, 12, 22 are front ends, 1
3, 23 are intermediate frequency (IF) amplifiers and FM detectors, 3
1 is an A channel 1 / B channel 2 switching controller, 32
Is a switch, 33 is a stereo demodulator, 34 to 36 are audio amplifiers, 37 to 39 are speakers, and 40 is a multiplex signal demodulator.

FIG. 7 shows an example of a specific configuration of the switching controller 31 shown in FIG. 6, wherein 51 and 52 are ripple component detectors, 53 and 54 are negative rectifiers, 55 and 56 are adders, and 57 is a comparator. It is.

In FIG. 1, VA is a DC voltage (S-meter voltage) output from the IF amplifier & detector 13 in proportion to the input electric field strength, and vA is a ripple component superimposed on the DC voltage VA. The AC voltage increases as the multipath disturbance increases, and VA ′ is the sum of the DC voltage VA and the DC voltage obtained by negatively rectifying the AC voltage vA.

FIG. 8 shows the relationship between the DC voltage VA ' and the AC voltage vA. These VA, vA and VA 'are voltages on the A channel side. VB, vB and VB '
Is the voltage on the B channel side, and VA, vA, V
A '.

The DC voltage VA ′ of the A channel and the DC voltage VB ′ of the B channel are compared by a comparator 57, and
When A '>VB', the switch 32 is switched so that the detection output of the A channel is selected, and when VA '<VB', the detection output of the B channel is selected.

FIGS. 9A and 9B show the relationship between the S-meter voltage VA (VB) and the ripple component vA (vB) with respect to the input electric field strength, respectively. FIG. 10 shows a relationship between a ripple component and an input electric field strength in a state corresponding to a case where multipath interference is added (a state where AM is added to an FM signal).

In the example shown in FIG. 6, the IF amplifier & detector 13,
The input electric field level is detected from the 23 S-meter voltage, the degree of multipath interference is detected from the ripple component superimposed on the input electric field level, and a channel having a good reception state is selected from the A and B channels. .

[0010]

However, the amplitude level of the ripple component superimposed on the S-meter voltage is different from that shown in FIG.
As shown by 0, the amplitude varies depending on the input electric field strength and is not constant. Therefore, the amplitude level becomes large at a certain electric field strength and becomes small at another electric field strength. That is, generally, the ripple component superimposed on the S-meter voltage has a peak point or a dip point depending on the electric field intensity.
For this reason, when detecting the degree of multipath interference based on the ripple component superimposed on the S-meter voltage, it is difficult to adjust the setting of the detection sensitivity, and if the received electric field strengths of both the A and B channels are different, it is not necessarily required. There is a problem that a channel with small multipath interference is not always selected.

Another conventional multipath interference detection method for detecting a high-frequency component of the FM detection output, which is conventionally performed, is about 61 kHz to 91 kHz for FM multiplex broadcasting.
Because there are multiple signals up to kHz, higher 100 kHz
From the above, it is necessary to detect, and there is a problem in terms of an efficient detection level (a distinction between triangular noise of FM detection output and noise due to multipath interference).

An object of the present invention is to provide an FM receiver capable of detecting multipath interference without depending on the input electric field strength and free from malfunction due to multiple signals.

[0013]

Means for Solving the Problems] To achieve the above object, FM receiver of the diversity scheme of the present invention, multiple
A plurality of antennas, a plurality of FM receiving means for receiving signals from the antennas, converting the signals into a predetermined intermediate frequency, and performing FM detection to obtain a detection output signal, and selectively receiving signals from the FM receiving means. Signal selection means for outputting,
Provided for each of the FM receiving means, from the detection output signal
An integral multiple of the pilot signal frequency and no broadcast signal component
Hand to extract the multipath interference component of standing city frequency domain
Stage and the multi-path and means for detecting the interference component level corresponding to the amount of interfering components and outputs a disturbing component level signal, the detected the FM reception electric field intensity level from the received signals
Means for outputting an electric field strength level signal for each means, and selection control means for controlling a selection operation of the signal selecting means by a control signal generated based on the interference component level signal and the electric field strength level signal. It is characterized by.

[0014]

According to the present invention, the input electric field strength is compared with each S-meter voltage of a plurality of channels, and the degree of multipath interference is compared from the FM detection output. Can be selected, so that multipath interference can be detected and compared without depending on the input electric field strength.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of an FM receiving apparatus according to the present invention. In the figure, reference numerals 14 and 24 denote bandpass filters, and the rest is the same as the conventional example of FIG.

FIG. 2 shows a specific example of the configuration of the attendant switching control unit 31 shown in FIG. 1. In the conventional apparatus, the ripple component detection is obtained from the S-meter voltage. It is obtained from the FM detection output that has passed through the filters 14 and 24. VA, vA,
Relationship VA '(VB, vB, VB ') is the same as the conventional example of FIG.

FIGS. 3A and 3B show the relationship between the S-meter voltage VA (VB) and the output vA (vB) of the 57 kHz bandpass filter 14 (24) with respect to the input electric field strength according to the present invention. A in FIG. 3B shows a weak electric field portion,
This shows how a weak electric field noise is generated at the output of the 57 kHz bandpass filter.

FIG. 4 shows the relationship between the 57 kHz band-pass filter output vA (vB) and the input electric field strength in a state where multipath interference is added. The output vA (vB) changes depending on the degree of multipath interference (depending on the amplitude ratio, phase difference, delay time difference, etc. of the direct and reflected waves of the multipath), and does not depend on the electric field strength.

FIG. 5 shows an example of an FM detection output frequency spectrum of a receiver when FM multiplex broadcasting is received. FIG. 5A shows a case where there is no multipath, and FIG. 5B shows a case where there is a multipath. Is shown. In FIG. 5, for simplification of the description, a stereo modulated signal in which a single sine wave fA is added to only the left or right channel and a multiplexed signal are used. (A)
When there is no multi-path, the sum signal f is output to the FM detection output.
A, pilot signal 19 kHz difference signal 38 kHz ± fA,
Each spectrum of the multiplex signal 61 kHz to 91 kHz exists. On the other hand, when there is the multipath of (b), in addition to the above-mentioned spectrum of (a), a multipath interference causes an interference spectrum centered on a frequency that is an integral multiple of 19 kHz. The level of this jamming spectrum is
It depends on the degree of modulation of the audio signal fA, the amplitude ratio of the multipath direct wave and the reflected wave, the phase difference, the delay time difference, and the like.

Since a multiplex signal has a frequency spectrum of about 61 kHz to 91 kHz, a multipath interference causes a problem in that an interference spectrum is generated around 76 kHz at the center. The interference spectrum due to multipath also occurs at 19 kHz, 38 kHz, 57 kHz, 95 kHz, and the like.

In the embodiment of the present invention shown in FIG. 1, 57 kHz band-pass filters 14 and 24 are provided, and a 57 kHz component (57 kHz ± 4 kHz) of a multipath interference spectrum is provided.
Band component). 57 kHz band pass filters 14 and 24 are IF amplifiers & FM detectors 13 and 23
With the M detection output as an input, a 57 kHz component is detected from the multipath interference spectrum, and this is supplied as a ripple component input to the channel switching control unit 31. As the S-meter voltage input of the channel switching control unit 31, the S-meter voltage (DC) is supplied from the IF amplifiers & FM detectors 13 and 23.

Therefore, in the embodiment of the present invention, the multimeter is controlled by the S meter voltages of the A channel and the B channel.
Compare the input electric field strength considering the effects of path disturbance.
As a result, a signal having a good reception state is selected from both the A and B channels.

According to the above-described embodiment, the following effects can be obtained. (1) Multipath interference can be detected and compared without depending on the input electric field strength. (2) A malfunction due to the FM multiplex signal does not occur. (3) The detection sensitivity of the multipath interference amount can be easily set.
That is, as compared with the method of detecting the ripple component included in the S-meter voltage, when multipath interference does not occur, there is no interference spectrum, so that the sensitivity setting can be easily adjusted. In the embodiment described above, the antenna is 2
Although the case of the number is shown, the number is not limited to two, and generally a plurality may be provided and selected from them.

[0024]

As described above, according to the present invention, it is possible to detect multipath interference without depending on the input electric field strength in the diversity type FM receiver, and to prevent malfunction due to multiplex signals. Especially detection of jamming signals
In the frequency domain that is an integral multiple of the pilot signal frequency
By doing so, multipath interference components can be detected efficiently
Wear.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an FM receiving apparatus according to the present invention.

FIG. 2 is a configuration diagram showing an example of a specific configuration of a part of FIG. 1;

FIG. 3 is a diagram showing a relationship between an S-meter voltage and an output of a 57 kHz band-pass filter with respect to an input electric field strength according to the present invention.

FIG. 4 is a diagram showing a relationship between a 57 kHz band-pass filter output and an input electric field strength in a state in which multipath interference is added according to the present invention.

FIG. 5 is a diagram illustrating an example of an FM detection output frequency spectrum of a receiver when an FM multiplex broadcast is received.

FIG. 6 is a configuration diagram of a conventional FM receiving apparatus.

FIG. 7 is a configuration diagram showing an example of a specific configuration of a part of FIG. 6;

FIG. 8 is a diagram showing a relationship between a DC voltage VA ′ and an AC voltage vA.

FIG. 9 is a diagram illustrating a relationship between an S-meter voltage and a ripple component with respect to a conventional input electric field strength.

FIG. 10 is a diagram illustrating a relationship between a ripple component and an input electric field strength in a state corresponding to a case where conventional multipath interference is applied.

[Explanation of symbols]

 11, 21 antenna 13, 23 IF amplifier & FM detector 14, 24 57kHz band pass filter 31 A channel / B channel switching control unit 32 switch

Continuation of the front page (56) References JP-A-58-79345 (JP, A) JP-A-57-135533 (JP, A) JP-A-61-69225 (JP, A) JP-A-2-179129 (JP) JP-A-2-159833 (JP, A) JP-A-1-171139 (JP, U) JP-A-1-91353 (JP, U) (58) Fields studied (Int. Cl. ⁷ , DB H04B 1/10-1/14 H04B 15/00-15/06 H04B 7/00 H04B 7/02-7/12 H04L 1/02-1/06

Claims (1)

(57) [Claims] 1. A plurality of antennas, and inputs the received signal from the antenna, and a plurality of FM receiving means for obtaining a detection output signal to FM detection and converts to a predetermined intermediate frequency, from said FM receiver a signal selecting means for outputting a signal selectively provided for each of the FM receiver, from the detection output signal
An integral multiple of the pilot signal frequency and no broadcast signal component
Hand to extract the multipath interference component of standing city frequency domain
Stage and the multi-path and means for detecting the interference component levels outputs a disturbing component level signal corresponding to the amount of interfering components, the FM receiving and detecting the electric field intensity level from the received signals
Means for outputting an electric field strength level signal for each communication means, and selection control means for controlling a selection operation of the signal selecting means by a control signal generated based on the interference component level signal and the electric field strength level signal. A FM receiver of a diversity system.