JPS5834060B2 - Multi-pass switch couch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multipath observation device suitable for use in an FM receiver.

First, a conventional multipath observation device for FM broadcast waves will be explained below with reference to FIG.

In FIG. 1, an FM broadcast wave is received by an antenna 1, the received signal is supplied to an FM front end 2 and converted into an intermediate frequency signal, and this intermediate frequency signal is sent to an intermediate frequency amplifier 3,
The signal is supplied to an intermediate frequency amplification circuit 34 having a multi-stage configuration consisting of 4 and 5, where it is amplified, and then supplied to a frequency discriminator 6 where it is demodulated.

This demodulated signal is supplied to a multiplexer circuit 7, which outputs a left signal and a right signal.

On the other hand, a portion of each output signal from the intermediate frequency amplifiers 3 and 4 is separately supplied to rectifier circuits 7 and 8, where they are rectified, combined, and smoothed by a smoothing circuit 9.

Reference numeral 12 denotes an oscilloscope, and a low frequency signal corresponding to the amplitude component of the received signal, which is an output signal of the smoothing circuit 9, is supplied to a terminal 10 and further supplied to a vertical deflection plate of the oscilloscope 12 via a terminal 11.

The demodulated signal from the frequency discriminator 6 is also supplied to the horizontal deflection plate of the oscilloscope 12 via terminals 13 and 14.

When no multipath occurs, a single horizontal line is drawn on the cathode ray tube of the oscilloscope 12.

In addition, 15 is the multipath observation terminal 10°1 of the FM receiver.
3 is a terminal board, and 16 is a terminal board having input signal supply terminals 11 and 14 of the oscilloscope 12.

However, according to the conventional multipath observation device mentioned above,
It has the following drawbacks:

When FM broadcast waves arrive at a receiver accompanied by multipath interference, the received radio waves are generally phase modulated and amplitude modulated.

The amplitude modulation component of the received signal taken out as a multipath observation signal at the terminal 10 changes depending on the depth of frequency modulation of the FM broadcast wave, so the strength of the signal to be observed changes from moment to moment, resulting in multipath interference of the received signal. It is not possible to clearly observe the degree of

Furthermore, due to the influence of each limiter operation by the intermediate frequency amplifiers 3, 4, and 5 in each stage, the multipath observation signal obtained at the terminal 10 changes depending on the strength of the received signal.

That is, when the received signal strength is low, the output signal of the FM front end 2 is subjected to a limiter action at the later stage of the intermediate frequency amplifier 34, and when the received signal strength is high, the output signal is subjected to a limiter action at the latter stage of the intermediate frequency amplifier 34. The front and rear ends of the shaft are designed to receive limiter action.

As a result, in the case of Figure 1, the multipath observation signal has bimodal characteristics depending on the received signal strength, and since it changes depending on the received signal strength, the degree of multipath interference in the received signal can be clearly observed. Can not.

In view of this, the present invention utilizes the fact that the harmonic signal components of subchannel signals of FM broadcast waves increase when multipath interference occurs, and reduces the degree of multipath interference in the received signal regardless of the received signal strength. The purpose of this project is to provide a multipath observation device that can clearly observe the

Hereinafter, an embodiment in which the present invention is applied to an FM receiver will be described with reference to FIG.

In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals and will be explained.

FM broadcast wave, that is, L+R+3L-R)・ωt Sinωj + p Sin 2 (L and R are left and right signals, respectively, ω is the subcarrier angular frequency, t is time,
An FM broadcast wave obtained by FM modulating the main carrier signal with a stereo composite signal (p is the amplitude of the pilot signal) (a pilot tone broadcast wave) is received by antenna 1,
The received signal is supplied to the FM front end 2 and converted into an intermediate frequency signal, and this intermediate frequency signal is supplied to a multi-stage intermediate frequency amplifier 34 and amplified, and then supplied to the frequency discriminator 6. demodulated.

This demodulated signal, that is, the stereo composite signal, is supplied to a multiplexer circuit 7, which outputs a left signal and a right signal.

Then, a part of the output of the frequency discriminator 6 is transmitted to the first and second
is supplied to the bandpass filters 21 and 1γ.

The first bandpass filter 21 is provided so as to pass only the channel signal with the highest frequency, that is, the subchannel signal (LR) Sillωt among the composite signals demodulated by the frequency discriminator 6.

This subchannel signal is supplied to an amplifier 22 and amplified, and then supplied to a diode 23 and detected.

Then, the detection output of the diode 23 causes the capacitor 24 to
is charged.

The second band-pass filter 17 is configured to pass only the desired harmonic signal of the high-frequency channel signal, that is, the harmonic distortion signal of the sub-channel signal, among the middle legs of the composite signal demodulated by the frequency discriminator 6. The frequency band is approximately 70 KHz to 150 KHz.

This harmonic distortion signal is supplied to an amplifier 18 and amplified, and then supplied to a diode 19 and detected.

Then, the detection output of the diode 19 causes the capacitor 2 to
0 is charged.

26 a t 26 b are switching transistors as a switching circuit, each emitter of which is grounded, and each collector of which is connected to a diode 23 and a capacitor 2.
4 connection midpoint, diode 19 and capacitor 20
are connected to the connection midpoints of each.

Reference numeral 25 denotes an astable multi-by-break for controlling these transistors 26a and 26b, and its output is supplied to each base of the transistors 26a and 26b.

These transistors 26a and 26b cause the charges in the capacitors 24 and 20 to be discharged at a predetermined frequency.

Reference numeral 12 denotes an oscilloscope as a means for supplying the detection outputs of the respective outputs of the first and second low-pass filters 21 and 17 to obtain a ratio.

Then, the terminal voltage of the capacitor 24 is detected by the oscilloscope 12.
The terminal voltage of the capacitor 20 is supplied to the vertical deflection plate of the oscilloscope 12.

Thus, an intermittent sawtooth wave voltage as shown in FIG. 3A is applied to the horizontal deflection plate of the oscilloscope 12, the amplitude of which changes depending on the level of the subchannel signal.

Further, an intermittent sawtooth wave voltage as shown in FIG. 3B, which is synchronized with that in FIG. It changes depending on.

Therefore, a triangular waveform is drawn on the display surface of the oscilloscope 12 as shown in FIG.

The length of the base of this triangular waveform changes in proportion to the level of the subchannel signal.

The angle θ between the oblique side and the base of this triangular waveform changes depending on the degree of multipath interference of the received signal.

That is, when the degree of multipath interference of the received signal is small, the angle θ is small, and when the degree is large, the angle θ is large.

This is because the FM broadcast waves are amplitude modulated by multipath interference.

This angle θ is independent of the level of the subchannel signal.

Note that even if there is no multipath interference at all, harmonic signals exist due to modulation distortion of, for example, 5% of the subchannel signal, but the angle θ of the triangular waveform due to this influence is extremely small.

Thus, according to the device shown in Fig. 2, by observing the angle θ of the triangular waveform on the display surface of the oscilloscope, multiplexing of the received signal can be accurately determined regardless of the strength of the received signal and regardless of the degree of modulation. The degree of path interference can be clearly observed.

Another embodiment of the invention will now be described with reference to FIG.

In FIG. 5, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and redundant explanation thereof will be omitted.

In FIG. 5, a divider 33 is provided in place of the oscilloscope 12 in FIG. 2 as a means of supplying the detected outputs of the respective outputs of the first and second bandpass filters 21 and 17 to obtain a ratio. This is the case.

This divider 33 will be explained below.

The anode of the diode 19 is connected to the output terminal of the amplifier 18 , the cathode of the diode 19 is connected to one end of the capacitor 20 whose other end is grounded, and the P-channel field effect transistor in the divider 33 27 and one end of resistor 28.

The other end of resistor 28 is connected to power supply -VDD.

Further, the anode of the diode 23 is connected to the output terminal of the amplifier 22, and the cathode of the diode 23 is connected to the capacitor 24.
It is connected to one end of , and also to the gate of field effect transistor 27 in divider 33 .

The other end of the capacitor 24 is grounded, the drain of the field effect transistor 21 is connected to the input end of an operational amplifier 29, and one end of a resistor 31 whose other end is grounded, and the output end of the operational amplifier 29 is It is connected to its input end via a resistor 30 and also to a meter 32, the other end of which is grounded.

Next, the operation of the apparatus shown in FIG. 5 will be explained.

The detection output of the diode 19 is supplied to the source of a P-channel field effect transistor 27, and the detection output of the diode 23
The detected output is supplied to the gate of the field effect transistor 27.

The source of the field effect transistor 27 is connected to the power supply -VDD.
A predetermined voltage is applied from the resistor 28 to the resistor 28.

The output signal taken out from the drain of the field effect transistor 27 is amplified by an operational amplifier 29 and then sent to a meter 32.
supplied to

The divider 33 includes the first and second bandpass filters 21.17
The ratio of the detection output of each output is obtained as follows.

That is, the voltage supplied to the drain of the field effect transistor 27 by the detected output of the output of the second bandpass filter 17 is set to the voltage supplied to the gate of the N1 field effect transistor 27 (VI), and the voltage supplied to the gate of the N1 field effect transistor 27 is The resistance value of the resistor 30 which is the feedback resistor of the amplifier 29 is Rf, and the drain of the field effect transistor 27 which is the input resistance of the operational amplifier 29 is Rf.
When the source-to-source resistance is Ri, the output voltage Vo of the operational amplifier 29 can be expressed as in equation (1).

It can be expressed as

In other words, this output voltage ■o is the ratio of the detection outputs of the respective outputs of the first and second bandpass filters 21 and 17, and
2.

Thus, according to the apparatus shown in FIG. 5, by observing the deflection of the needle of the meter 32, multipath interference of the received signal can be detected accurately, regardless of the strength of the received signal, and regardless of the degree of modulation. It is possible to clearly observe the degree of

According to the apparatus of the present invention described above, it is possible to reliably observe the degree of multipath interference of a received signal, regardless of the level of the received signal, and regardless of the degree of modulation.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing a conventional multipath observation device;
The figure is a system diagram showing one embodiment of the multipath observation device of the present invention, FIG. 3 is a waveform diagram, FIG. 4 is a waveform diagram of the display screen of an oscilloscope, and FIG. 5 is another embodiment of the multipath observation device of the present invention. FIG. 2 is an example system diagram. 21 and 17 are first and second band pass filters, 12 is an oscilloscope as a means for obtaining a ratio, and 33 is a divider as a means for obtaining a ratio.

Claims (1)

[Claims] I L+R+(L-R) sinωt+psin”L
! , (where L and R are the left and right signals, respectively, ω is the subcarrier angular frequency, t is time, and p is the amplitude of the pilot signal) in the stereo composite signal (L
-R) a first bandpass filter passing through sxnωt;
a second bandpass filter that passes a desired harmonic signal of the subchannel signal (L-R) sxnωt; and a detection output of each output of the first and second bandpass filters. 1. A multipath observation device comprising: means for obtaining a ratio, and the state of multipath interference is observed based on the ratio.