JPS6033632Y2 - multipath detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multipath detector particularly suitable for receivers used in car stereos and the like.

Conventionally, in order to detect the presence or absence of multipath occurrence, high frequency components included in the detection output of the receiver, for example 100kHz, are used.
By detecting the above distortion and noise components, the presence or absence of the multipath has been detected.

However, although the above method is relatively effective in detecting multipath in a medium-weak electric field, it cannot detect multipath in the case of multipath generated under a weak electric field, as explained below.

That is, when the electric field level at the time of generation is 50 to 70 dBμv or more, the S/N of the received signal is good, and the distortion component (output)
In some cases, the absolute value of becomes small, making it impossible to detect multipaths.

Furthermore, since it is not possible to distinguish between a normal state under a medium-weak electric field and a multipath generation state under a strong electric field, multipath detection is often impossible when noise other than multipath occurs, such as ignition noise. It was possible.

On the other hand, it is known that when multipath noise occurs, the amplitude component of the carrier drops, so by detecting this, multipath noise can be detected.

However, once the signal passes through the intermediate frequency amplifier, the amplitude remains constant due to a limiter within the intermediate frequency amplifier, so it has not been possible to detect a drop in the amplitude component under a strong electric field.

The present invention has been made to eliminate the above-mentioned drawbacks and to make it possible to detect changes in the amplitude component. A detector that performs automatic gain control of an intermediate frequency amplifier and detects the amplitude component of the received input and the average voltage of the carrier, a level adjuster that adjusts the output from the detector, and the level adjuster. It consists of a voltage comparator that compares the detected output of the amplitude component passed through the carrier with the average voltage of the carrier, and outputs a multipath control signal when the detected output of the amplitude component is lower than the average voltage of the carrier. The purpose of this invention is to provide a multipath detector with

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating a first embodiment of an antenna receiving system to which a multipath detector according to the present invention is applied, in which 2 is an antenna side terminal, 3 is an RF amplifier, 4 is a mixer, 5 is an oscillator, and 6 7 is an intermediate frequency amplifier, 7 is an MPX decoder, 8 is an output terminal for the left channel, 9 is an output terminal for the right channel, and 10 is a multipath detector.

In the multipath detector 10, 11 is a second intermediate frequency amplifier including a bandpass filter provided in parallel with the intermediate frequency amplifier 6, and 12 is a first detector for detecting the amplitude component in the output. 13 is a second detector for detecting the average value voltage of the carrier; 14 and 15 are level adjusters corresponding to the first detector 12 and second detector 13, respectively; 16 is a level adjuster A voltage comparator 17 is an output terminal for outputting a multipath control signal.

As mentioned above, the second intermediate frequency amplifier 11 does not have a limiter because it uses the amplitude component of the output as information, but instead has a second limiter to keep the output voltage approximately constant. Automatic gain control is applied from the wave detector 13.

FIG. 2 shows the multipath detector 10 used in the above embodiment.
In this timing chart, A is the waveform of the detection output sent from the mixer 4 to the multipath detection circuit 10, B1 is the output waveform of the amplitude component that has passed through the level adjuster 14, and B2 is the waveform that has passed through the level adjuster 15. C is the output waveform of the average value voltage of the carrier, and C is the output waveform of the multipath control signal output to the output terminal.

Next, the function of detecting multipath noise in the antenna receiving system shown in FIG. 1 will be explained.

When multipath noise occurs during reception, an amplitude component appears in the output A from the mixer 4, as shown in FIG.

The output A is transmitted through the second intermediate frequency amplifier 11 and the detector 12.
, via the level adjuster 14, becomes the detected output B1 of the above amplitude component shown in FIG. Become.

The voltage comparator 16 compares the detected output B1 and the detected output B2, and outputs the multipath control signal C from the output terminal 17 when the detected output B1 becomes lower than the detected output B2.

In the multipath detector 10 according to the present invention, even if the transmitting station is far away and the electric field becomes low, there is no problem because the detection output B2 used as the reference voltage decreases.

Furthermore, by adjusting the level adjusters 14 and 15, it is possible to make the reproduced sound insensitive to amplitudes that do not affect practical use.

Therefore, malfunctions due to spatial noise etc. can be prevented.

FIG. 3 is a circuit diagram illustrating another embodiment 300 of the multipath detection circuit according to the present invention, in which 301 is a low-pass filter for intermediate frequency bypass, 302 is a low-pass filter for bypassing the intermediate frequency, and 302 is a circuit diagram for smoothing the amplitude component to obtain an average value of the carrier. A low-pass filter for obtaining an output voltage according to the voltage, 303 is a voltage comparator, 304
305 is a level adjuster configured with a variable resistor for adjusting the detected output of the amplitude component, and 305 is a level adjuster configured with a variable resistor for adjusting the average value voltage of the carrier.

306 is an input side terminal from the second intermediate frequency amplifier 11, 307 is an output terminal for a multipath control signal, 308 is a power supply terminal, and 309 is an output terminal for an automatic gain conversion signal.

310. 311, 312, 313 are resistors with predetermined values, 314, 315 are coils, 316, 317, 318
319 is an electrolytic capacitor, 320 is a transistor, and 321 is a diode.

In the above embodiment, the terminals 321 .
322 are supplied with the detected output B1 of the amplitude component and the average value voltage B2 of the carrier shown in FIG. 2 from the level adjusters 304 and 305, respectively.

In the multipath detection circuit 300, the level adjuster 30
When the detected output B1 from the level adjuster 305 becomes lower than the detected output B2 from the level adjuster 305, the voltage comparator 303 outputs a multipath control signal to the output terminal 307.

As explained above, the present invention accurately outputs multipath control signals even under strong electric fields, and furthermore,
It has a relatively simple circuit configuration and the sensitivity to multipath noise can be easily adjusted, making it particularly suitable for a detection circuit for multipath countermeasures in car stereos.

In addition, it can be produced separately from the receiver and installed as an adapter if the listener desires, which is very effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating a first embodiment of an antenna reception system to which a multipath detector according to the present invention is applied, and FIG. 2 is a block diagram illustrating the operation of the multipath detector 10 used in the first embodiment. The timing chart, Figure 3, is
FIG. 3 is a circuit diagram of an embodiment 300 of a multipath detection circuit. 3...-RF amplifier, 4...mixer,
5... Oscillator, 6, 11... Intermediate frequency amplifier, 7... MPX decoder, 10...
...Multipath detector, 12.13...Detector, 14,15,304,305...Level adjuster, 16,303...Voltage comparator, A, B
l, B2. C・・・・・・Output waveform, 301°30
2...Low pass filter.

Claims (2)

[Scope of utility model registration request] (1) In an antenna reception system, a second intermediate frequency amplifier without a limiter is provided in parallel with the intermediate frequency amplifier, automatic gain control is performed on the second intermediate frequency amplifier, and the amplitude component of the reception input and the carrier are It consists of a detector that detects the average voltage of the carrier, a level adjuster that adjusts the output from the detector, and a voltage comparator that compares the detected output of the amplitude component with the average voltage of the carrier. Multipath detector. (2) The detector comprises a low-pass filter for intermediate frequency bypass and a low-pass filter for obtaining an output voltage according to the average voltage of the carrier. path detector.