JPS6340374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes FM signals directly coming from a transmitting antenna.
FM that arrives after being detoured and delayed due to reflection that mixes with the wave and causes so-called FM multipath distortion in the received output.
Regarding the display measurement method of multipath disturbance waves, in particular,
Display of multipath interference waves The FM wave to be measured can be measured under normal modulation conditions, without using a specific modulation signal to create a special test condition, regardless of the modulation signal or radio wave propagation condition.
It is designed to display and measure specifications such as delay time of multipath interference waves with respect to direct waves, relative strength, and phase difference when not modulated.

Generally, when receiving FM modulated radio waves such as FM broadcast waves, the desired wave that arrives directly from the transmitting antenna is reflected by mountains, buildings, etc., and travels through a different path than the desired wave, that is, a propagation path. When receiving FM waves mixed with interference waves that arrive after a certain delay, so-called multipath distortion occurs in the FM demodulated output signal of the FM receiver. This FM multipath distortion is greatly influenced by the delay time, unmodulated phase difference, and relative strength of the interfering wave with respect to the desired wave, that is, the delay time, phase difference, and DU ratio, each of which will be abbreviated below. Therefore, the above-mentioned three types of multipath interference waves at the input end of the FM receiver
If these elements can be measured, it is possible to quantitatively understand the degree of multipath distortion, which in turn can help determine whether the receiving antenna is installed properly or not, and whether the receiving antenna in use is Effective reception countermeasures can be taken, such as checking whether the configuration is appropriate. Furthermore, it is also possible to clarify the basic data necessary to cancel and eliminate multipath distortion using the circuit configuration of an FM receiver.

Conventionally, methods for measuring FM multipath interference waves in order to understand the extent of such multipath distortion have been broadly classified into the following two measurement methods. The first measuring method uses an indicating meter, and two examples of the configuration of a receiving measuring circuit that performs measurements using such a meter are shown in FIGS. 1 and 2, respectively.

The configuration example shown in Figure 1 uses envelope detection to detect and rectify the amplitude change in the received FM wave that occurs due to multipath interference waves being superimposed on the desired wave, and then indicates this to the meter. In addition, the configuration example shown in Fig. 2 is a receiver for FM stereo broadcast waves, and the 19KHz included in the FM demodulated output signal is
The pilot signal component of
This system instructs the meter to output directly according to the phase difference between the Hz signal components.

However, all of the conventional multipath interference measurement methods using the reception measurement circuit configured as described above have the following drawbacks.

In other words, in the first measurement method using a meter, the value indicated to the meter does not accurately correspond to the degree of occurrence of multipath distortion. Since the ratios are not expressed individually, it is insufficient to use it as a mere guideline for determining the degree of multipath distortion occurrence.

Next, the second conventional measurement method is to make an oscilloscope draw a Lissage figure related to multipath distortion. The envelope detector 9 is provided in addition to the horizontal axis input terminal of the FM receiver.
The envelope detection output signal is sent to the oscilloscope 14.
The required data is read by observing the Lissage figure obtained by supplying the data to the vertical axis input terminal of the . In other words, while the time axis of the oscilloscope is swept by the FM demodulated output signal consisting of a regenerated modulated signal in the low frequency range, the envelope detection output signal representing the amplitude change of the composite wave of the desired signal and the interference wave is detected on the vertical axis of the oscilloscope. 4, a Lissage figure consisting of a stationary single waveform is obtained as shown in FIG. Therefore, if the delay time of the interference wave relative to the desired wave is τ, the phase difference is τ, and the DU ratio is 1/r, then the relationship between these three elements and the Lissage figure is shown in Figure 4. Since this holds true, the three elements related to multipath interference waves can be accurately measured based on this relationship.
In addition, when reading these three elements from the Lissage figure, it is necessary to know the scale of the time axis of the Lissage figure, but the angular frequency indicated by the point obtained when the oscilloscope's time axis sweep stops when the FM wave is not modulated. The time axis scale of the Lissage figure can be determined from the position of ω ₀ and the time axis sweep width corresponding to the value of the maximum angular frequency deviation ω _M.

Therefore, even if the reproduced modulation signal that performs the time-axis sweep is composed of several types of frequency components, the Lissage figure drawn as described above will not work as described above if the modulation frequency is in a low frequency range. Similarly, it becomes a stationary Lissage figure. However, as the modulation frequency increases, even if the modulation frequency is stationary, it is no longer possible to obtain a Lissage figure that can be read with three elements as shown in Figure 4.
The image becomes a figure as shown in the figure, making it impossible to read the three elements. Furthermore, the modulation frequency and delay time τ
If a certain relationship exists, the resulting Lissage figure may represent a constant value independent of the angular frequency and become a straight line parallel to the time axis.

Therefore, as mentioned above, it is possible to obtain a Lissage figure whose three elements can be read by using, for example, FM
Regarding broadcast waves, this is a special case in which a test radio wave modulated with a low frequency signal is transmitted using a subharmonic oscillator at night after the broadcast ends, and the general modulated signal during program broadcasting is speech or music. Since the program sound consists of program sounds such as Since the signal is a complex signal with a complex waveform, the obtained Lissage figure is a complex multiplexed figure as shown in FIG. 6, and it is impossible to read three elements.

As is clear from the above, the second multipath interference measurement method, in which three elements are read from the Lissage figure, has been conventionally only applicable to special test conditions, which is an important problem in implementation. There was a drawback.

It is an object of the present invention to eliminate the above-mentioned conventional drawbacks, and to create a test condition using a special modulation signal consisting of a special modulation frequency component when reading three elements of multipath interference waves from a Lissage figure as in the past. It is an object of the present invention to provide a method for displaying and measuring FM multipath interference waves, which allows the state of multipath interference waves to be accurately and easily measured using everyday commercial FM waves without having to do so.

Another object of the present invention is to provide a method for displaying and measuring FM multipath interference waves, which enables reliable and easy measurement of the three elements of FM multipath interference waves and facilitates consideration of measures to eliminate FM multipath distortion. It's about doing.

That is, the FM multipath interference display measurement method of the present invention draws a static, simple waveform Lissage figure in relation to FM multipath distortion, regardless of the modulation frequency of the modulation signal in the FM wave or the number of types thereof. In addition, the detection output signal of the envelope detector provided in the FM receiver is supplied to the vertical axis of the oscilloscope, and the FM receiver can be read out accurately and easily. In displaying and measuring the state of multipath interference in the received FM waves based on a Lissage figure drawn by supplying the signal component derived from the FM demodulator of the oscilloscope to the horizontal axis of the oscilloscope,
Integration of the difference between delayed and non-delayed demodulated output signals corresponding to the amount of delay between two FM waves arriving via the multipath of the FM demodulator, or corresponding to the amount of delay of the demodulated integrated output signal of the FM demodulator. 2FM by finding the difference between delayed and non-delayed
The present invention is characterized in that a difference in phase shift between waves is formed and supplied to the horizontal axis of the oscilloscope.

The invention will be explained in detail below by way of example embodiments with reference to the drawings.

First, FIG. 7 shows an example of the configuration of an FM wave reception and measurement apparatus for implementing the method of the present invention. In the FM wave reception measurement device with the configuration shown in the figure, the normal FM
The demodulated output signal of the FM demodulator 6 of the FM wave receiving circuit configured in the same manner as in the receiver is guided to the delay calculation circuit 15 which operates as described later by the configuration described later, and is processed by the oscilloscope 14.
The envelope detector 9, which is added before the amplitude limiter 5, generates an envelope representing the amplitude change of the input FM wave due to the superposition of the FM multipath interference wave. The detected output signal is taken out and supplied to the vertical input terminal V of the oscilloscope 14, and a Lissage figure is drawn on the display screen of the oscilloscope 14, allowing the reading of three elements of the FM multipath interference wave as described later.

The delay arithmetic circuit 15, which constitutes the main part of the FM reception and measurement apparatus for carrying out the method of the present invention with the above-described configuration, is configured as shown in FIGS. 8 and 9, for example. That is, in the delay arithmetic circuit 15 having the configuration shown in FIG. 8, the FM demodulated output signal is split into two branches, one branch output signal is directly led as is to the subtracter 17, and the other branch output signal is variable. After being delayed by the delay time τ of the multipath interference wave via the delay circuit 16, it is also led to the subtracter 17. The subtracter 17 performs subtraction to subtract the latter from the former, supplies the difference output signal to the integrator 18 for integration, and uses the integrated output signal as the output signal of the delay calculation circuit 15, as described above. is supplied to the horizontal input terminal H of the oscilloscope 14.

Furthermore, in the delay calculation circuit 15 having the configuration shown in FIG. 9, the FM demodulated output signal is subjected to almost the same delay calculation processing as in the configuration shown in FIG. This is different from the configuration shown in FIG. 8 in that the variable delay circuit 16 and the subtracter 17 perform the delay subtraction operation after the above is applied in advance.

By appropriately selecting and adjusting the delay time of the variable delay circuit 16 in the delay calculation circuit 15 according to each of the configuration examples described above, the Lissage figure drawn on the display screen of the oscilloscope 14 can be
Regardless of the modulation frequency of the modulation signal in the FM wave or the number of types thereof, for example, as shown in FIG. 11, the Lissage figure is a waveform that is almost single and always stationary. In other words, there is no need to use a special test condition using a modulation signal consisting of a special frequency component as in the conventional second measurement method described above, and it is possible to use a normal commercial modulation condition, for example. Regarding FM broadcast waves, regardless of whether they are monaural broadcasts or stereo broadcasts, it is possible to always draw a stationary Lissage figure consisting of an almost single simple waveform in the state of daily program broadcasting, and therefore, The three necessary components of the multipath interference wave, namely the delay time τ, the phase difference, and the DU ratio 1/r, can be accurately and easily read from a stable and clear Lissage figure as shown in FIG.

The operating principle of the display and measurement method of the present invention, which enables the above-mentioned remarkable effects to be obtained, will be explained in detail below.

First, for the sake of a simple explanation, assume that the modulation signal of the FM wave consists of a single frequency, and let that modulation signal be F(t).F(t)=Acos2πf _n・t Here, A is the modulation is the amplitude of the signal and f _n is the modulation frequency. Also, if the amplitudes of the desired wave and interference wave are E ₁ and E ₂ , respectively, then Desired wave: E ₁ sin (ω ₀ t + D/f _n sin2πf _n・t) Interference wave: E ₂ sin {ω ₀ (t - τ )+D/f _n sin2πf _n (t-τ)
} =E ₂ sin {ω ₀ t+D/f _n sin2πf _n (t−τ)−
} Here, ω ₀ is the angular frequency of the carrier wave, D is the amplitude A
is the frequency deviation corresponding to .

Further, ω ₀ τ=2nπ+ (n is a positive integer).

Therefore, when the interference wave is added to the desired wave, the DU
Since the ratio is E ₁ /E ₂ = 1/r, the composite wave e _a is The envelope detection output signal for such a composite wave e _a is
Assuming A _put and the FM demodulated output signal as F _put , Here, the first term on the right side of the FM demodulated output signal _Fput is a modulation signal component, and the second term is a distortion component caused by multipath interference waves. However, since the value of the second term is generally extremely small compared to the value of the first term, the FM demodulated output signal is guided to the horizontal input terminal of the oscilloscope as described above, and the envelope detection output signal is When drawing a Lissage figure by introducing the FM demodulated output signal F put to the vertical input terminal, assuming that F _put ≒ D cos2πf _n t , the value F _put ′=2π Dcos2πf _n t obtained by multiplying this FM demodulated output signal F _put by π is applied to the horizontal input terminal of the oscilloscope. The second conventional measurement method described above is such that the amount of light is supplied to the user. Therefore, in the second conventional measurement method, when the modulation frequency is low, it can be regarded as sinπf _n τ≒πf _n τ 2πf _n t−πf _n τ≒2πf _n t, and the envelope detection output Signal A _put
is, A _put ≒E ₁ √1+ ² +2 {2
2 _n +} Here, when normalized with respect to E ₁ as A _put /E ₁ = A _put ′, the normalized envelope detection output signal A _put ′ is A _put ′≒√1+ ² +2 {・_put ′+} becomes. Therefore, as mentioned above, if the modulation frequency is in a low range, the horizontal sweep input signal of the oscilloscope will be included in the vertical deflection input signal as is, and a stationary single Lissage figure will be drawn. Become.

For such a Lissage figure, for example, as shown in FIG. 4, three elements of multipath interference waves,
That is, the delay time τ, the phase difference when no modulation, and
Find the DU ratio 1/r.

Therefore, the normalized envelope detection output signal A _put ′ is
τ・F _put ′+=0, that is, at F _put ′=−/τ, therefore, at a point distanced by −/τ from the vertical axis that appears when there is no modulation where F _put ′=0, the maximum value 1+r The minimum value 1-r is obtained at a point distanced from the point -/τ by π/τ. If such maximum value points and minimum value points are read with respect to the vertical axis when no modulation is performed, the three elements of the multipath interference wave, namely, the delay time τ, the phase difference, and the amplitude ratio r, can be obtained by calculating backwards from the above-mentioned relationship. be able to.

Next, in the conventional second measurement method mentioned above, when the modulation frequency becomes high, a stationary single Lissage figure cannot be obtained, and the figure becomes complex, making it impossible to read the three elements mentioned above. is the expression of the normalized envelope detection output signal A _put ′ even if its modulation frequency is single. Regarding 2D _/ f _n sinπf _n τcos _{( 2πf n} t−πf _n τ _{) in} It cannot be considered that τ≈2πf _n t , and therefore, it cannot be considered that it is approximately equal to 2πDτ cos2πf _n t as described above.

On the other hand, the horizontal axis sweep input signal of the oscilloscope is
F _put ′=2πDcos2πf _n t, and this value and the above equation for the normalized envelope detection output signal A _put ′
Comparing the value in cos { }, we find that |2D/f _n sinπf _n τ|≦2πDτ, so even if the horizontal sweep input signal changes, the frequency of the vertical axis deflection input signal does not change sufficiently. figure,
In some cases, the maximum value is 1+ as shown in Figure 5.
It becomes impossible to take r or the minimum value 1-r.

Also, cos( _{2πf n}
t−πf _n τ) in the horizontal axis sweep input signal F _put ′
Compared to the value of cos2πf _n t, the phase is significantly delayed by πf _n τ, so at two different times
cos(2πf _{n t} −πf _n
τ) are not equal values, so the Lissage figure obtained at that time is, for example, the 10th
The result will be a double figure as shown in the figure.

Next, as mentioned above, the reason why the Lissage figure obtained when the modulation signal consists of multiple frequency components becomes a complex multiplex figure as shown in FIG.
Let f _n1 , f _n2 , ......, f _nM be the frequency deviations due to their modulation frequencies as D ₁ , D ₂ , ......, respectively.
If D _M , becomes. Therefore, in the case where the modulation frequency is single, if the single modulation frequency changes and the values of f _nk and D _k in the above equation differ, the double figure shown in FIG. All of them are different, but since the above equation is made up of M frequencies including f _nk and D _k with their different values, the mutual influence of those values is also included, but Therefore, the horizontal axis sweep input signal on the oscilloscope
The temporal change in F _put ′ and the change in the value of cos { } in the vertical axis deflection input signal A _put ′ have an extremely complicated correspondence, resulting in a complex multiplex figure as shown in Figure 6. will be drawn.

As is clear from the detailed explanation above, in the conventional second measurement method, a stationary single Lissage figure is measured by the horizontal axis sweep input signal F _put ′ and the vertical axis deflection input signal A _put ′ of the oscilloscope. It is only possible to read the three elements of multipath interference waves as shown in the figure when using a special test radio wave in which the modulation signal consists of only low frequency components. The drawback was that it was impossible to grasp the state of disturbance occurrence.

However, the disadvantage of the second conventional measurement method is that the envelope detection output, which changes in relation to the three elements of the multipath interference wave, is used as the horizontal axis sweep input signal of the oscilloscope using the vertical axis deflection input signal as the FM demodulation signal. The purpose is to draw a Lissage figure by supplying the output signal as it is. The present invention focuses on this point, and conventionally supplies the signal to the horizontal input terminal of the oscilloscope in its original form.
Appropriate arithmetic processing is applied to the FM demodulation output so that the function is the same as that contained in the vertical axis deflection input signal, and the phase shift of the desired wave and interference wave that arrived via multipath is calculated. A signal of the form 2D/f _n sinπf _n τcos (2πf _n t−πf _n τ) corresponding to the difference is formed from the FM demodulated output signal. Letting this phase shift difference be _n , the normalized envelope detection output signal A _put ′ is Since the oscilloscope's vertical axis input signal A _put ' is synchronized with the synchronization of the period _n of the horizontal axis sweep input signal, it always draws a constant trajectory and remains constant regardless of the modulation state of the modulation signal. A stationary single Lissage figure will be drawn. An example of such a Lissage figure in the display measurement method of the present invention is shown in FIG. In the Lissage figure shown, _n +=0, that is, _n =-
When A _put ′ becomes the maximum value 1+r, and furthermore,
The minimum value is 1-r at _n =-+π. Now, considering the maximum value of the phase shift difference _n , since |sinπf _n τ|≦πf _n τ, | _n |=|2D/f _n sinπf _n τcos (2πf _n t−πf _n τ)
|≦2πDτ, and therefore −2πDτ≦ _n ≦2πDτ.

Three elements of the multipath interference wave, namely the delay time τ, the phase difference, and the intensity ratio r, can be determined from the Lissage figure shown in FIG. 11 drawn as described above. Therefore, in order to form the above-mentioned phase shift difference _n as a horizontal axis sweep input signal for drawing a Lissage figure on the oscilloscope, for example, as shown in FIG. First, the delay calculation circuit 15 consisting of the FM demodulation output signal and the integrator 18
F _put ≒Dcos2πf _n t is delayed by a time equal to the delay time τ of the multipath interference wave, and Dcos2πf _n (t−
τ) and subtracting the delayed output signal from the FM demodulated output signal, Dcos2πf _n t−Dcos2πf _n (t−τ) = −2Dsinπf _n τsin (2πf _n t−πf _n τ). Then, when the subtracted output signal is integrated, it becomes 1/2π·2D/f _n sinπf _n τcos (2πf _n t−πf _n τ). Here, 1/2π can be removed by providing a gain adjuster and multiplying by 2π, so the required phase shift difference is 2D/f _n sinπf _n τcos (2πf _n t−πf _n τ). can get.

Next, in the configuration example of the delay calculation circuit 15 shown in FIG. 9, as described above, the integration in the calculation processing described above is applied to the FM demodulated output signal in advance, and then the signal processing of delay and subtraction is performed. This is done so that a delay calculation output signal _n that is exactly the same as in the configuration example shown in FIG. 8 can be obtained.

Note that the above description applies even when the modulated signal is composed of a plurality of frequency components. Furthermore, the above arithmetic processing can also be performed by logical calculations using digital circuits, and it is not necessarily necessary to use analog processing as shown in the figure.Furthermore, when observing a Lissage figure, a waveform storage device can be used instead of an oscilloscope. It is also possible to immediately calculate and display the three elements of the multipath interference wave, that is, the delay time τ, the phase difference, and the intensity ratio r, using a minicomputer. Furthermore, by connecting such a signal processing circuit device to the variable delay circuit 16, the delay time can be automatically changed and fixed as described later.

As is clear from the above explanation, according to the present invention, the FM
The three elements of multipath interference waves, namely delay time τ, phase difference, and
The DU ratio 1/r can be measured, and since these three factors significantly affect the degree of multipath distortion, accurate understanding of these three factors will help prevent FM multipath distortion. Whether or not the receiving point, that is, the installation position of the receiving antenna is appropriate, whether the directional characteristics of the receiving antenna in use are sufficient to avoid multipath interference waves, or whether there is any special This can greatly contribute to determining whether reception countermeasures are required or not. Furthermore, by knowing the delay time τ of multipath interference waves, it is possible to determine which reflecting objects cause multipath interference waves, based on the distance relationship between the transmitting point and the receiving point and the value of this delay time τ.
For example, it is also possible to estimate the location of a high-rise building.

Furthermore, by applying the display measurement method of the present invention
The FM receiving circuit can also be configured to remove FM multipath distortion occurring in the FM demodulated output signal of the FM receiver, and several examples of FM receiving circuits with such configurations will be shown below.

First, in the FM receiving circuit having the configuration shown in FIG. 12, the delay calculation circuit 15 having the configuration shown in FIG.
In addition to displaying and measuring multipath interference waves using the same configuration as the circuit device according to the present invention shown in FIG. FM by calculation processing by circuit 19
Multipath distortion components are removed from the demodulated output signal. That is, using the delay time and intensity ratio identified from the observation of the Lissage figure described above using an oscilloscope, the cancellation calculation circuit 19 accurately cancels out and removes the multipath interference components.

In addition, in the multipath distortion removal device having the configuration shown in FIG. 13, the cancellation calculation circuit 1
Using the output signal of 9, the delay time τ of the variable delay circuit 16 included in the delay calculation circuit 15 and the variable delay circuit included in the removal calculation circuit 19 can be adjusted in conjunction with each other, thereby eliminating multipath distortion. Since the FM demodulated output signal is used as the horizontal axis sweep input signal of the oscilloscope 14, a more accurate Lissage figure can be drawn, and the accuracy of the measured values can therefore be significantly improved.

In addition, in the multipath distortion removal device having the configuration shown in FIG. 14, the configuration shown in FIG. 12 is expanded to enable automatic identification of the delay time τ. The variable delay circuit 16 is controlled by the output signal of the multipath identification section 20 consisting of a computer.Furthermore, in the multipath distortion removal device having the configuration shown in FIG. 15, the configuration shown in FIG. 13 is expanded. As described above, the specifications of multipath interference waves can be automatically identified.

[Brief explanation of the drawing]

Figures 1 and 2 show the conventional method using an indicator meter.
FIG. 3 is a block diagram showing the configuration of a circuit device for implementing the FM multipath distortion measurement method, and FIG. 4, 5, and 6 are diagrams respectively showing aspects of Lissage figure display by the circuit device, and FIG. 7 is an example of the configuration of the circuit device implementing the FM multipath interference wave display measurement method of the present invention. FIGS. 8 and 9 are block diagrams showing examples of the configuration of the delay calculation circuit in the circuit device, and FIG. 10 shows the process of forming the multiple Lissage figure shown in FIG. 6. 11 is a diagram showing the mode of Lissage figure display by the circuit device shown in FIG.
13, 14, and 15 are block diagrams respectively showing configuration examples of an FM multipath distortion removing apparatus to which the method of the present invention is applied. 1... Receiving antenna, 2... High frequency amplifier, 3
... Mixer, 4 ... Intermediate frequency amplifier, 5 ... Amplitude limiter, 6 ... FM demodulator, 7 ... Low frequency amplifier, 8 ... Local oscillator, 9 ... Envelope detector, 1
0... Rectifier, 11... Meter, 12... 19KHz
Band pass filter, 13... Multiplier, 14... Oscilloscope, 15... Delay calculation circuit, 16...
variable delay circuit, 17... subtractor, 18... integrator, 19... removal calculation circuit, 20... multipath identification section.

Claims (1)

[Claims] 1. The detection output signal of the envelope detector provided in the FM receiver is supplied to the vertical axis of the oscilloscope, and the signal component derived from the FM demodulator of the FM receiver is supplied to the horizontal axis of the oscilloscope for drawing. In order to display and measure the state of multipath interference in the received FM waves based on the Lissage figure, the delayed and non-delayed waves corresponding to the amount of delay between the two FM waves arriving via the multipath of the FM demodulator are used. A difference in phase shift between the two FM waves is formed by integrating the difference between the demodulated output signals or by calculating a difference between delayed and non-delayed signals corresponding to the delay amount of the demodulated integrated output signal of the FM demodulator. A method for displaying and measuring FM multipath interference waves, characterized in that the signal is supplied to the horizontal axis of the oscilloscope.