JPS59194543A - Method for measuring separation degree of am stereophonic signal - Google Patents

Abstract

PURPOSE:To improve sharply measuring accuracy by applying a low frequency signal and a signal at the same level but different in phase by 90 deg. to two inputs of an AM stereophonic signal generator and measuring the level ratio of upper and lower side- band waves of the output on the primary side. CONSTITUTION:A low frequency signal 54 is applied from a main output terminal 52 of a low frequency oscillator 51 to an R signal input terminal 56 of the AM stereophonic signal generator 58, and a signal 55 different in phase from that of the signal 54 by 90 deg. is applied from a QUAD output terminal 53 to an L signal input terminal 57. A voltmeter 59 with an expanded scale measures both the signal levels so as to uniform the levels to adjust the output level of the oscillator 51 correctly. An AM stereophonic signal 60 of the generator 58 is measured by a spectrum analyzer 61 and the level ratio of the upper and lower side-band waves on the primary side is measured and designated as the separation degree from the channel L to the channel R. Subsequently, the signal L is reversed, the modulation degree of the L+R system is multiplied by prescribed times and the level ratio of the upper and lower waves on the primary side is measured by the analyzer 61 to use the measured value as the separation degree from the channel R to the channel L.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is based on the Magnavox method (8ivi-PM method) approved by the FCC (Federal Communications Commission).
This invention relates to a method for measuring the degree of separation of AM stereo signals, which is used to measure the degree of separation of an AM stereo signal generator.

The configuration of the conventional example and its problems Figure 1 shows the Magnavosox type AM stereo signal generator (
1 is a configuration diagram showing the principle of an AM stereo signal generator (hereinafter simply referred to as an AM stereo signal generator). The configuration and operation thereof will be explained below.

In FIG. 1, 1 is a left input terminal for stereo signals, and 2 is a right input terminal for stereo signals. Left signal 710 input to left signal input terminal 1 (hereinafter referred to as L signal) 3
, and the right signal (hereinafter referred to as R signal) 4 applied to the right signal input terminal 2 is applied to the matrix circuit 5,
(I, + R,) signal 6° (L-R) signal 7 is created. (The L-1() signal 7 is sent to the phase modulator 8 and applies phase modulation to the carrier wave oscillated by the carrier wave oscillator 9. The (L+f'L) signal 6 is phase modulated by the (L-R) signal 7. Delay circuit 1 for correctly adjusting the time relationship between
1 and is applied to the amplitude modulator 12. Amplitude modulator 12
applies amplitude modulation to the PM modulated wave 10 using the (L+R) signal 6. This is the AM stereo signal 13 of the Magnavox system, and is taken out from the output terminal 14.

Normally, as shown in Figure 2, to measure the degree of separation of AM stereo signals, a standard AM stereo signal generator 21 is created, a demodulator 22 is calibrated using that signal, and the calibrated demodulator is used to generate the AM stereo signal under test.
A method is adopted in which the degree of separation of the stereo signal generator 23 is measured.

A conventional calibration example for establishing the M stereo signal generator 21 to the standard at this time will be explained with reference to FIG.

In order to analytically determine the degree of separation of the standard AM stereo signal generator 21, at least 411 of the following items are required.

(1) Measuring the degree of separation of the matrix circuit (2) Measuring the degree of amplitude modulation (3) Measurement of the degree of phase modulation ['64I] Constant (4) Swing 1tlt? Measuring the time difference between I modulation and phase modulation (
6) Measurement of parasitic phase modulation during amplitude modulation (6) Measurement of parasitic amplitude modulation during phase modulation However, in such conventional methods, the calibration of the standard is very complicated and the resulting It is difficult to obtain a value of about 40 dB or more, and considering the value of 60 to 7 odB, which is desired as a standard device, it is hardly satisfactory.

OBJECTS OF THE INVENTION The present invention is intended to eliminate the drawbacks of the above-mentioned conventional examples, and aims to significantly improve measurement accuracy.

Structure of the Invention In order to achieve the above-mentioned object, the present invention calculates signals of the same frequency and the same level with a 90' phase difference as an L signal and an R signal. The relationship is based on the fact that the signals are at the same level with a 900 phase difference, and one side wave is eliminated by the principle of acid-containing SSB.In this case, the degree of separation can be measured from the level ratio of the upper and lower side waves. To clarify this, the degree of separation is measured by measuring the level of the upper and lower side waves using a spectrum analyzer.

According to the present invention, the conventional limit of about 40 dB can be reduced to 70 dB.
dB or more, it can be easily measured, and it has a very large effect.

Explanation of Examples First, 90 as the L signal and R signal, which are the basis of moxibustion.
0 Same level signal with different phase e 7JII station building, + on one side of Magnavox AM stereo signal wave
1-! : + Indicates that the wave will be canceled.

When the signals are combined, the (L+R) signal 6 is ■spt.

5intrno. t, (L-)1) Signal 71 lost 0s (pt → -) = Sln (pt + π)
.

If the modulation index 'lf: m2, then the PM modulated wave 10:v
2(t) is V2(t)=sin iω,,t +m2sin(pt
+π month=:T () (1'n2) S j Ifω
, 1±J1 (m2-5inl(cc+.±p)t±π
)±72 (m2) 51 mouths ((ω.±2p)t±2π
)...(1) Then, the Magnavox AM stereo signal 13:
Vl(t) is Vl(t)== +0(m2)+1 +m1sin(p
t4) 1 sinω. t±π) +J2(m2)11+m1sin(pt+-)lsin
l(ω.±2p) t +2yr 1・・・・・・(2
) ・・・・・・(3) From now on, the primary upper and lower waves 1-10(11112)5 CO3l (t
o , +p ) t +z 1+11(m2) sinl
(ω.+p)t+π1+41(m2)cosl(ω.

+p)t+-1...(4) However, due to the properties of the Bessel function, J2(m2)+T. (m2) = J1 (m2) Since it is defined as ml-m2 in the Magnabox method, ...... (5γ and mm, the -th lower side wave is canceled. At this time, the -th lower side wave 1'O(''2)-dicosl(ω.-p)t--122-J 1 (rn2)s+01 (ω.-p)t-π
)+l2(rr12)・dicosl(ω.-p)
t --122 1-1J. (m2)−−+11(m2)−J2(rfL2
)・shi12 2cos
l (ω.-p)t--1 (6). However, Jo)■2°Next, consider the case where the L signal 3 and the R signal 4 are reversed. If we perform a calculation similar to the above calculation, -th lower side wave = Jo(m
2)・-cosl(ω.-p)t-H3P-J1(m2) cos((ω.-p)t-Fl+ 7
2 (Z112)・m, C, S, (ω, -p)t+-
122 = (Jo (m2) - ■, (m2) - 12 (m2) Chi c
osl(θ). -p)t--1 = -2J2(m2)5cosl (ω,-p)t-1
22 ・・・・・・(7) Primary upper and lower waves = 2J1(m2)cosl(c+>.+p
) t+71 ・----(B) Although V is not eliminated redundantly, 50% modulation C by L signal or R signal
(L+R): 25 channels, (L-R): 26 channels], the ratio of the primary upper and lower side waves is 42 dB, and it can be said that the side waves are almost eliminated. Strictly speaking, by doubling, the −th order lower side wave is completely eliminated.

Next, we will clarify that the level ratio of the -th order upper and lower side waves corresponds to the degree of separation.

(5) Relationship between the degree of separation due to the level difference between the (L+R) system and the (L-R) system and the level ratio of the primary upper and lower side waves (L+R) system gain is GM (GM-m12m1 is the modulation of the (L+R) system If the total gain G8 (Gs=m22m2 is the modulation index of the (L-R) system) and (L-R), equation (6)' becomes... (9), and (6 ) formula becomes...(IQ).Therefore, it follows from formula (9) I (10).

Above, L signal 3. Let's consider a case where a signal with the same level but 900 points different is applied to R signal 4.

Next, when an AM stereo signal generator with a gain of G for the (L+R) system and a gain of Gg for the (L-R) system is modulated with only the L signal 3, and it is received by the ideal receiver 48 Iso, Find the separation formula.

In FIG. 3, the input signal 33: VLS applied to the L signal input terminal 31, the R input signal 34' applied to the R signal input terminal 32, and VH2 are (L+R) inputs in the ideal magnetic IJ circuit 36. Signal 36: VMS
and (L-11() input signal 37'', VB2,
The M stereo modulator 38 generates the M stereo signal 4o, and the ideal reception/detection circuit 41 generates the (L+R) output signal 42:
vM.

(L-)L) Output signal 43: VSO and L output signal 4 at ideal matrix circuit 44. E5: VL.

and R output signal 46': becomes VRO and is taken out from L output terminal 47 and R output terminal 48. It's a waste, 39
indicates an AM stereo signal generator, and 49 indicates an ideal receiver.

Here, the gain I of the (L+R) system of the M stereo modulator
GM, (L-R) system gain kG3+, and the state where the input signal is only VLS ("R8-〇)? Think about it. Then, v33:■LS-vR8"vLS vSQ:GS@■5S0GS"vLS From now on, the stereo separation degree :S is expressed by equations (11) and (12), and the level ratio of the primary upper and lower side waves when a signal of the same level that is 90' ahead of the R signal is added to the L signal represents the degree of stereo separation. The level ratio of the L signal and the R sidewave similarly represents the degree of stereo separation.

(B) Relationship between the degree of separation due to the phase difference between the (L + R) system and the (LR) system and the level ratio of the primary upper and lower side waves In Figure 1 VC, the (L + R) signal 6 is at t:ospt
- Melt. Equation (2) is: Vl(t)=lo(tn2)h+m1sin(p
t+-month sinω, t±J1("2n11+rn1si
n(pt+-)1s+n1(c+). ±p)t ±π±
ψ )±T2(m2) 11+In1sin(pt+
-) 1S Group 1 (OJ C±2pJt±2π±2ψI
...(14) If we rearrange this in the same way as in (8), -water side wave = -J. (m2) e-j, cos l (ω.

+p)t+; 1...(16)...(16) Here, 10) Under the condition of J2, perform an approximation to delete the top of J2 (m2), and set (L +, R- river system's use inke GM, (L-R) system's gain f G s as 5, (
One phrase style.

Rewriting equation (16), we get... (17) +11(m2)cosl(cu.-p)t----ψ)・
...(18) From now on, it becomes . This result also holds when the phase relationship between the L signal and the F signal is made the same. (Under the condition that Jo>12) Next, in Fig. 3, the AM stereo modulator (L+R)
Let us consider a state in which the gain of is 1, the gain of the (LR) system is 1/ψ, and the input signal is only vLs (V us =O). Then, VMS=■LS+vR8:vLs (vSS"vLS -VB2"VLS VSO= 1 lψIIvss=vLs/ψFrom now on, the degree of separation: S becomes from equation (19) and equation (2o), and the L signal and R signal The level ratio of the primary upper and lower side waves when signals of the same level but with a 900 degree phase difference are expressed as the stereo separation degree.

Furthermore, the same result is obtained when V L B = O and only VB8 is used.

Next, when the L signal is delayed by one, and when it is -advanced, 2
Let us fully clarify the meaning of the degree of separation in 2. (100% modulation of the L-J signal in the Magnavox system is 1 rad, and in equation (3), ■1) ■2. J3.・・・・・・
Therefore, if we ignore everything after ■2, equation (3) becomes =JO(
m2) S1nω. t-J. (m2) - cosi (cuc+p)t+-1
22 +71(m2)sjn l (ω.+p)t+π)-J
l(m2)5cosl (ωo+2p)t+-122 1 +Jo (m2)'', CO3((ω.7p)t-
, -1-11(rl12) 5I11 + (ω.-p
) as -π)-Jl(m2)5cosf'(ω.-2p
)t--122 (blank space below) ・・・・・・(21) However, due to the property of Bessel function, J, (m2) + Jo(m
2) If we focus only on the primary upper and lower side waves of equation (21), these are made up of the carrier wave, (L+R) signal, and (L-R) signal, so (L+R)i signal gold*(L+R)
+ (L-R) signal k V (L-R) (!: L, (
L+R)4M+(LR) The relationship between the signal and the side waves is expressed as follows.

*CL+R)=K CCO3t (ω.+p)t-i+
cosl(ω.-p)t-H)](*(L-fL)-K Ccosl(ω.+p
)t −= l+cosl (ω.−p)t−2;−)
]・・・・・・(22) L signal @9, R signal is *R, -up side wave: (
The terms of the primary upper and lower side waves in equation 21) are expressed in equation (21) and (22).
From formula... (24) (From formula 23 and formula (24), the formula for the degree of separation in this case is V
RI, which represents the degree of separation from the L channel to the R channel. Furthermore, when the phase relationship between the L signal and the R signal is reversed, the degree of separation from the R channel to the L channel is similarly required.

As mentioned above, the Magna Bonox AM stereo system 1f
The degree of stereo separation from the L channel to the R channel of the signal generator is achieved by simultaneously adding signals of the same level with a 90° phase difference as the iR signal with the different phase and the L signal with the leading phase. It is obtained by measuring the level ratio of the primary upper and lower side waves of the M stereo signal at this time. Conversely, the degree of separation from the R channel to the L channel is that the one with the leading phase is the R signal.

By using the delayed iL signal, it can be determined from the level ratio of the -blown upper and lower side waves. However, the degree of separation of the matrix circuit within the AM stereo signal generator that generates the (L+R) signal and (LR) signal from the L signal and the R signal must be sufficiently greater than the measurement unity. Also, Fig. 4 shows an example of measuring the degree of separation of a Magnavox type AM stereo signal generator using the method of the present invention for dividing water from the R channel to the L channel based on the above considerations. Use and explain. In FIG. 4, a low frequency signal 54:cospt'(i-
In addition to the R signal input terminal 66 of the AM stereo signal generator 58, the low frequency signal ts 5 from the QUAD output terminal 53:
cos (pt+-) is added to the signal input terminal 57. The output level of the low frequency oscillator 51 is adjusted correctly by measuring with a voltmeter 59 with an enlarged scale so that both signal levels are the same. Observe the AM stereo signal 60 of the AM stereo signal generator 58 with the spectrum analyzer 61, measure the level ratio of the upper and lower side waves (from the HL channel to the R
Let it be the degree of separation into channels. Next, reverse the L signal and (L
+R) modulation degree of the system). The level ratio of the primary upper and lower side waves is determined using a spectrum analyzer, and the R channel is separated into the L channel. After that, the modulation degree of the (L + R) system is returned to its original state.

Effects of the Invention The present invention is a method for separating Ah stereo signals of 11,111 feet using the Magnavox system as described above, and provides the following effects.

(a) Measurement accuracy, which was conventionally limited to about 40 dB, can be significantly improved to 20 to 30 dB with a simple method.

(b) What used to be a very complicated calibration process is now very simple.

(C) Direct measurements can be made without having to perform two calibrations: calibrating a standard AM stereo signal generator and then calibrating the entire demodulator using it.

(d) The effect obtained by this is not only connected to an improvement in the accuracy of the signal generator (it also has a ripple effect of helping to improve the quality of AM stereo broadcasting).

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of the Magnavox type AM stereo signal generator, Figure 2 is a wiring diagram explaining the conventional separation measurement method, and Figure 3 is the ideal output signal of the Alvi stereo signal generator. FIG. 4 is a wiring diagram when receiving signals at a receiver. FIG. 4 is a block diagram when measuring the stereo separation degree of an AM stereo signal generator using the method of the present invention. 1... Left side signal input terminal, 2... Right side signal input terminal, 5... Matrix circuit, 8...
... Phase modulator, 9 ... Carrier wave oscillator,
11... Delay circuit, 12... Amplitude modulator, 21... Standard AM stereo signal generator, 22
... Demodulator, 23 ... AM stereo signal generator under test, 36 ... Ideal matrix circuit,
38...AM stereo modulator, 39...
・AM stereo signal generator, 41...Ideal reception/detection circuit, 44...Ideal matrix circuit, 4
9...Ideal receiver, 51...Low frequency oscillator, 68...AM stereo signal generator 2, 5
9... Voltmeter with enlarged scale, 61... Spectrum analyzer. Name of agent: Patent attorney Toshio Nakao and 1 other person-2
(

Claims (1)

[Claims] AM that phase-modulates a carrier wave with the difference signal between the radial signal and the H signal, and modulates the phase-modulated modulated wave with a modulation degree equal to the modulation index of the phase modulation using the sum signal of the radial signal and the R signal. In order to define the degree of separation in the stereo signal generator, a low frequency signal and a low frequency signal having a phase difference of 900 degrees from the low frequency signal are input to each of the two signal input terminals of the AiVI stereo signal generator at the same level. Adjust and mark〃[j
A method for measuring the degree of separation of AM stereo signals, characterized in that the degree of separation is determined by the level ratio of the upper and lower primary side waves of the M stereo signal obtained from the AM stereo signal generator.