RU2332781C1 - Method of single-sideband signal transmission - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used for radio signal transmission by means of single-band modulation (SBM). Method of single-sideband signal transmission is characterised by the fact that medium frequency and medium radio frequency harmonic oscillation are generated; the first SBM-signal component is generated in the first processing circuit as follows: SBM-signal in the first processing circuit is multiplied to medium radio frequency voltage, the first component of SBM-signal video frequency is selected, amplified, and the first operating video voltage is received. A harmonious signal of constant amplitude at medium radio frequency is voltage and power amplified with simultaneous change of its amplitude according to law of change of the first operating video voltage, at a time, the second SBM-signal component is generated in the second processing circuit as follows: SBM-signal in the second processing circuit is multiplied to medium radio frequency voltage phase-modified to π/2, the second component of video frequency is selected, amplified, and the second driving video voltage is received. Medium radio frequency harmonic signal is phase-modified to π/2 and amplified, then this voltage amplified signal is simultaneously power amplified, with its amplitude modified according to law of change of the second operating video voltage, then first and second components of SBM-signal being generated are added up and resultant output SBM-signal is supplied to emit to communication channel.

EFFECT: reduction of out-of-band emission while operation at high efficiency.

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Description

The invention relates to the field of radio engineering and can be used to transmit radio signals using single-band, as well as other types of modulation, in which amplitude and phase modulation are simultaneously present.

The problem of transmitting a single-band signal in radiocommunication devices is the simultaneous presence of amplitude and phase modulation in the transmitted signal, which leads to the choice of the linear operating mode of the transmitting device and, consequently, to a decrease in the efficiency of the transmitted signal (section "Single-band modulation" p .369 [1]). Increases in radio transmission efficiency are achieved by working in class D [1]. In this case, the efficiency is increased both due to the full use of the supply voltage of the anode (collector) circuit, and due to the key operation of the amplification device. The solution to the issues of increasing efficiency when working in class D in amplifiers of output stages is considered in detail, for example, in [2], where it is shown that pulse-width modulation (PWM) with filtering the output signal can be used to transmit amplitude changes. With this approach, a high gain in radio transmission is ensured. The message [3] develops the ideas of the operation of the terminal cascade in a class close to class D.

Known methods for transmitting amplitude-modulated (AM) signal in receivers operating in class D at a power of 0.5 kW, 1 kW and 2 kW, data on which are given in the publication of the company Broadcast Electronics Inc [4]. The information in them is transmitted not only in AM mode, but also in the transmission mode of two independent channels of information - the stereo mode, when information is simultaneously transmitted using amplitude modulation and carrier frequency modulation. But this method cannot be used to transmit a single-band signal, since in the amplitude modulation mode phase (frequency) modulation is not transmitted, and in the stereo mode the depth of the amplitude modulation is limited (less than 70%) and there is basically no connection between the signals in the channels, that is, these signals are transmitted independently. When transmitting a single-band signal, the amplitude change and phase change of the radio signal are tightly coupled, and the depth AM reaches 100%, while the amplitude changes from the maximum value to zero [5].

The closest in technical essence to the proposed method is a method of transmitting a single-band signal described in § books [5], adopted as a prototype.

The prototype method is as follows.

In accordance with the input information, a radio signal is generated (generated) in one sideband (OBP modulation). Further, the generated OBP signal undergoes transformations in two processing chains operating in parallel (simultaneously).

In the first processing circuit, the voltage of the OBP signal is limited in amplitude and amplified in voltage. In the second processing chain, the OBP signal is detected, and the resulting envelope of the OBP signal (video signal) is amplified. Then, two operations are simultaneously carried out: power amplification of a radio signal with a constant amplitude and a change in its amplitude according to the law of the envelope of the video signal. Next, the received OBP signal is radiated into the radio channel. These operations can be performed with high efficiency.

Note some methodological features. If the carrier frequency of a single-band signal is f ₀ , then there is no radiation at this frequency itself, but there is radiation in one of the side frequencies:

from (f ₀ + F _H ) to (f ₀ + F _B ) - the upper side strip,

or from (f ₀ -F _B ) to (f ₀ -F _H ) the lower side strip,

where F _H and F _B are the minimum and maximum modulation frequencies, respectively.

If the frequency is measured in radians, then given that ω = 2πf, we get:

(ω ₀ + Ω _Н ) to (ω ₀ + Ω _В ) - the upper lateral strip,

(ω ₀ - Ω _B ) to (ω ₀ - Ω _H ) is the lower lateral strip.

Usually in the shortwave range F _N = 0.3 kHz, and F _B = 3.4 kHz, which corresponds to the frequency band of the telephone channel.

The average radiation frequency will actually be shifted relative to the carrier frequency f ₀ by the frequency (F _H + F _B ) / 2 for transmission in the upper side band or minus (F _H + F _B ) / 2 for transmission in the lower side band.

To increase the efficiency of the transmitter, separate envelope amplification of the high-frequency signal and phase-modulated radio frequency voltage is used, which allows preliminary amplification of a limited-amplitude radio signal with high efficiency, as well as the possibility of power amplification of the output signal with high efficiency, for example, when working in class D and the implementation of the anode (collector) modulation of the envelope voltage [1].

However, there are drawbacks to this approach - significant out-of-band emissions. Consider the issue from the point of view of compatibility of the receiving and transmitting equipment within the same communication node. For clarification, we note that the level of out-of-band emissions (the sum of noise and interference) u _ШД at the receiver input in the frequency band of 3 kHz should not exceed (0.1 ÷ 0.2) μV. If we relate this voltage to the output voltage of the transmitter u _PRD , which at 500 kW is 500 V, we obtain the necessary attenuation of the transmitter voltage of 194 dB or a noise density of 230 dB / Hz. However, the obtained value should be reduced by the amount of isolation between the antennas, which is (15 ÷ 30) dB, therefore, the remaining (164 ÷ 179) dB should be provided by attenuation in the transmitter, namely the power amplifier and the filter at its output. High power filters with suppression of up to 80 dB exist and provide this suppression when tuning from the average frequency by ± (15 ÷ 20)% and their passband is ± (6 ÷ 8)%. However, these filters have a high cost and are not tunable in frequency. For this reason, in practice, the suppression of out-of-band transmitter emissions during detuning ± (15 ÷ 20)% is determined only by the parameters of the transmitter itself and the attenuation due to the territorial separation of the transmitting and receiving antennas. Thus, the reduction of out-of-band emissions in the transmission path is of great, and often crucial practical importance.

Let us dwell on the causes of out-of-band emissions. The essence of the problem is as follows.

The first reason is that although the spectrum of the original OBP signal is limited and rather narrow, since it is limited by the band of the low-frequency signal, the spectra of the envelope of the OBP signal and phase-modulated radio frequencies are obtained by nonlinear conversion, and are therefore infinite. Therefore, in the formation of the total spectrum (the convolution of these spectra), the components of the spectra must be mutually compensated in the frequency region where the original OBP signal is absent.

Let us consider in more detail the aforementioned method for transmitting a signal u (t) consisting of two harmonic oscillations of equal amplitude (1) or (2)

where a is the amplitude of each of the two harmonic signals;

ω ₀ = 2πf ₀ - carrier circular frequency of a single-band signal;

t is the current time;

Ω ₁ = 2πF ₁ and Ω ₂ = 2πF ₂ - deviation from the carrier frequency of the first and second harmonic signals, respectively.

In our case, without changing the generality, we introduce the definitions

F _H <F ₁ <F _B , F _H <F ₂ <F _B ;

F ₁ = F _H + ΔF, F ₂ = F _B -ΔF, where

в нашем случае будем в дальнейшем называть средней радиочастотой ω_ср.Frequency

in our case, we will hereinafter be called the average radio frequency ω _cf.

Figure 1 shows the dependence of voltage on time u (t) in accordance with expressions (1) and (2).

Здесь δ(х) - функция Дирака.Figure 2 shows the spectrum S (ω) of the considered signal u (t), which has two components: δ (ω _cf - Ω) and δ (ω _cf + Ω), where

Here δ (x) is the Dirac function.

Thus, initially, only two harmonic components are present in the signal, and out-of-band distortions are absent.

When the envelope of the high-frequency signal and the phase-modulated voltage of the radio frequency are separately amplified due to nonlinear detection and limitation operations, two causes of out-of-band emissions arise: firstly, the difference between the envelope delays and the oscillations at the middle radio frequency; secondly, the distortion of the envelope during its selection (amplitude detection) and amplification.

In paragraph 7.2 of the book [5], on the example of OM (OBP) of a signal composed of two sinusoidal oscillations: a sin (ω ₀ + Ω ₁ ) t and a sin (ω ₀ + Ω ₂ ) t of equal magnitude, it is shown that because differences in the envelope delay and oscillations at the average radio frequency ω _cf occur out-of-band emissions at frequencies detuned from the average frequency by (Ω ₂ - Ω ₁ ) _n , where n is the frequency harmonic number (Ω ₂ - Ω ₁ ), and the amplitude of the spectral components decreases inversely proportional to the value of n ² .

The second reason for out-of-band emissions is an error in extracting the envelope from the radio signal. The question of the accuracy of detection is considered, for example, in Ch. 8, §8.8. “Amplitude detection” of the book [6], where it is shown that the time constant during detection should be much less than the frequency of change of the low-frequency voltage, but on the other hand should be extremely small for the radio frequency. Failure to simultaneously fulfill these two conditions leads to nonlinear distortions. The “envelope zero suppression” type of these distortions is shown in bold lines in FIG.

The appearance of distortions of the type "suppression of the envelope zero" is due to the fact that the spectrum of the envelope z (t) of Fig. 3 is infinite, and the passband of the envelope during detection is fundamentally limited. If we do not take into account distortions during detection, then the envelope is cosine pulses. The Fourier expansion of cosine pulses is known, the coefficients of this expansion are called the Berg coefficients [6]. Figure 4 shows the decrease in the harmonic value of the signal with number n depending on the value of n, in our case, the cutoff angle γ is 90 °. As can be seen from the graph, at a frequency difference of 2 kHz, an attenuation of 80 dB is obtained with an offset of 8 MHz, and an attenuation of 100 dB at 70 MHz. This phenomenon is fundamentally present.

где n - номер гармоники.There are distortions of the radio frequency signal. The phase-manipulated signal is constant in amplitude, but abruptly changes in phase by π, that is, it has a spectrum of a rectangular pulse, in this case a meander. In this case, the harmonics (odd) decrease with speed

where n is the harmonic number.

To fulfill the condition of changing the phase of the radio frequency by 180 ° at the moment of the equality of the envelope to zero (see Fig. 1) it is necessary to achieve equal delays in the amplification circuits of the radio signal and its envelope with mathematical precision, and, in addition, to amplify the radio and video signal, have a frequency band radio and video amplifiers of infinite width, which is impossible. The presence of a time shift, as well as inaccurate allocation of the envelope shown in Fig. 3, will lead to the fact that after power amplification, the voltage (current) of the output signal changes abruptly, i.e., a component appears in the spectrum of the input signal, which decreases inversely with the detuning.

Therefore, the prototype method is ineffective in generating a transmission signal, since a single-band signal in this case has significant out-of-band emissions.

To address these shortcomings in the method of transmitting a single-band signal, including the input information, in accordance with which the signal is formed in one sideband (OBP signal), the conversion of the generated OBP signal in two parallel processing circuits and radiation into a radio channel, according to the invention generate a harmonic oscillation of the average radio frequency, as well as a harmonic signal with a constant amplitude at the middle frequency of the radio transmission; the first component of the OBP signal is formed in the first processing chain as follows: the OBP signal is multiplied with the harmonic voltage of the middle radio frequency, the first component of the video frequency is extracted from the received signal, which is the in-phase component of the OBP signal relative to the harmonic oscillation with the average radio frequency, then the first component of the video frequency is amplified and get the first control video voltage, while a harmonic signal with a constant amplitude at the middle frequency of the radio transmission amplify in terms of voltage, then at the same time they amplify in terms of power this voltage-amplified signal and change its amplitude according to the law of change of the first control video voltage; at the same time, the second component of the OBP signal is formed in the second processing circuit as follows: the OBP signal is multiplied with the harmonic voltage of the average radio frequency changed by π / 2 in phase, the second component of the video frequency, which is the quadrature component of the OBP signal, is extracted from the received signal relative to harmonic oscillations with an average radio frequency, then the second component of the video frequency is amplified and a second control video voltage is obtained, while the harmonic signal of the middle frequency of the radio transmitter cottages change in phase by π / 2 and the voltage increase, then simultaneously carry power gain of the amplified voltage signal and the change of the amplitude of the second control law changes videonapryazheniya; then the generated first and second components of the OBP signal are summed and the resulting output OBP signal is supplied for radiation to the radio channel.

The proposed method for transmitting a single-band signal is as follows.

In accordance with the input information, a radio signal is generated (generated) in one sideband (OBP modulation). In addition, a harmonic oscillation of the average radio frequency is generated, as well as a harmonic signal with a constant amplitude at the middle frequency of the radio transmission.

Further, the generated OBP signal is subjected to transformations in two processing chains operating in parallel.

In the first processing chain, the first component of the OBP signal is formed as follows. First, the OBP signal is multiplied with the harmonic voltage of the middle radio frequency; then, the first component of the video frequency, which is the in-phase component of the OBP signal with respect to the harmonic oscillation with the average radio frequency, is extracted from the received signal; Further, the obtained first component of the video frequency is amplified, and as a result, the first control video voltage is obtained. In this case, a harmonic signal with a constant amplitude at the middle frequency of the radio transmission is amplified by voltage. Then two operations are simultaneously performed: the power gain of this voltage-amplified harmonic signal with a constant amplitude at the middle frequency of the radio transmission and the change of its amplitude according to the law of the first control video voltage, resulting in the first (in-phase) component of the OBP signal.

At the same time, in the second processing chain, the second component of the OBP signal is formed as follows. First, the OBP signal is multiplied with the harmonic voltage of the middle radio frequency, the phase of which is previously changed to π / 2; then the second component of the video frequency is extracted from the received signal, which is the quadrature component of the OBP signal with respect to harmonic oscillations with the average radio frequency, then the obtained second component of the video frequency is amplified, as a result, the second control video voltage is obtained. In this case, a harmonic signal with a constant amplitude at the middle frequency of the radio transmission changes in phase by π / 2 and amplifies in voltage. Then two operations are simultaneously carried out: the power gain of this voltage-amplified harmonic signal with a constant amplitude at the average frequency of the radio transmission with the changed phase by π / 2 and the change of its amplitude according to the law of the second control video voltage, which results in the second (quadrature) component of the OBP -signal.

Next, the generated first and second components of the OBP signal are summed up and the resulting powerful output OBP signal is supplied for radiation to the radio channel.

The functional diagram of the device with which the proposed method is implemented is shown in FIG. 5, where the following notation is introduced:

1 - source of the OM signal;

2 and 12 - the first and second video frequency amplifiers;

3 and 13 - the first and second output cascades;

4 and 16 - the first and second blocks of pre-amplification;

5 - antenna;

6 - medium-frequency generator;

7 - generator of a medium frequency radio transmission;

8 and 10 - the first and second blocks of multiplication;

9 and 11 - the first and second filters of video frequencies;

14 and 15 - the first and second phase shifters on π / 2;

17 - adder.

The device with which the proposed method is implemented includes a first multiplication unit 8 connected in series, a first video frequency filter 9, a first video frequency amplifier 2 and a first output stage 3, the output of which is connected to the first input of the adder 17; the second multiplication unit 10, the second video frequency filter 11, the second video frequency amplifier 12 and the second output stage 13, the output of which is connected to the second input of the adder 17, the output of which is connected to the antenna 5., the input of the device is the input of the source of the OM signal 1, the output of which connected to the first inputs of the first 8 and second 10 blocks of multiplication. The output of the mid-frequency generator 6 is connected to the second input of the first multiplication unit 8, and through the first phase shifter by π / 2 14 to the second input of the second multiplication unit 10. The output of the medium-frequency radio transmission 7 through the first pre-amplification unit 4 is connected to the second input of the first output cascade 3, and through the second phase shifter connected in series to π / 2 15 and the second pre-amplification unit 16, with the second input of the second output stage 13.

The device with which the proposed method is implemented works as follows.

Information is supplied to the input of the device, according to which the source of the OM signal 1 generates a radio signal with OBP modulation with an average radio frequency ω _CP , which is simultaneously fed to the first inputs of the first 8 and second 10 multiplication units.

Block 6 produces a harmonic voltage of the middle radio frequency

Since Ω _Н = 2πF _Н and Ω _В = 2πF _В , where F _H and F _B are the minimum and maximum frequencies of the signal at the input of the device, respectively, we obtain

As a result of multiplication in block 8 of the OBP signal with a harmonic voltage of the average radio frequency ω _cf and subsequent filtering, the first component of the video frequency, which is the in-phase component of the OBP signal relative to harmonic oscillations with the average radio frequency, is allocated in the first video frequency filter 9. As a result of multiplying in block 10 an OBP signal with an output harmonic voltage of the average radio frequency ω _{CP of} block 6, which is phase-shifted by π / 2 in block 14, and subsequent filtering in the second filter of video frequencies 11, the second component of the video frequency is selected, which is the quadrature component of the OBP- signal relative to harmonic oscillations with an average radio frequency. In this case, the passband of the first 9 and second 11 filters of video frequencies (low frequencies) should ensure the passage of video frequencies, but suppress radio frequencies.

The in-phase video-frequency component from the output of the first filter of the video frequencies 9 is amplified in the first amplifier of the video frequency 2 and is fed to the first input of the first output stage 3, to the second input of which a harmonic signal at the medium frequency of the radio transmission ω _cp.per c of unit 7 is amplified by the voltage in unit 4 . In the first output stage 3, two operations are simultaneously performed: power amplification of the harmonic signal at the middle frequency of the radio transmission with a constant amplitude coming from the first pre-amplification unit 4, and the change of amplitude in accordance with change of the first control videonapryazheniya supplied from the first video frequency amplifier 2. The resulting first (in-phase) component of the SSB signal output from block 3 is fed to a first input of the adder 17.

The quadrature video-frequency component from the output of the second filter of the video frequencies 11 is amplified in the second amplifier of the video frequency 12 and is fed to the first input of the second output stage 13, to the second input of which a harmonic signal at the medium frequency of the radio transmission ω _{cf. perper} from block 7, passed through the second phase shifter to π / 2 15 and voltage-amplified in the second pre-amplification unit 16. In the second output stage 13, two operations are simultaneously performed: power-amplification of the signal coming from the output of the second block pre-amplification 16, and a change in its amplitude in accordance with a change in the second control video voltage supplied from the output of the second video frequency amplifier 12. The obtained second (quadrature) component of the OBP signal from the output of block 13 is supplied to the second input of block 17.

In block 17, the first and second components of the OBP signal are summed, the phases of which differ by 90 ° (vector addition). The received powerful OBP signal from the output of the adder 17 is fed to the antenna 5.

We show the effectiveness of the device to implement the proposed method. For a quantitative assessment, we consider the same case: the transmission of two sinusoidal oscillations a sin (ω ₀ + Ω ₁ ) t and a sin (ω ₀ + Ω ₂ ) t of equal magnitude [5].

Consider the case of equal frequencies for oscillators 6 and 7, since such an assumption does not affect the results of the consideration. In the particular case, the source of the OM signal 1 can generate a signal at the middle frequency of the radio transmission, then blocks 6 and 7 must be the same, which allows them to be combined in one block. However, in the general case, the average radio frequency and the average radio frequency are different.

As shown above, the sum of two oscillations can be represented in the form (2), i.e., as a product

where a is the amplitude of each of the two harmonic signals;

ω ₀ = 2πf ₀ - carrier circular frequency of a single-band signal;

t is the current time;

Ω ₁ = 2πF ₁ and Ω ₂ = 2πF ₂ - deviation from the carrier frequency of the first and second harmonic signals, respectively;

- средняя радиочастота ω_ср.

- the average radio frequency ω _cf.

Suppose for definiteness that Ω ₁ = Ω _H , and Ω ₂ = Ω _B (this does not reduce the generality of the consideration).

It can be seen from formula (3) that both factors are harmonic oscillations that do not have gaps in the derivatives, the spectrum of each oscillation is not infinite, but limited. In this case, the mutual time shift of the factors, unlike the prototype, does not change the spectrum of the output signal. Indeed, if a shift by an angle ξ occurs at the operating frequency, then formula (3) can be represented as

then from formula (4) we can obtain u (t) in the form of two oscillations

Thus, a phase shift of both harmonic components will occur, and their spectrum (energy spectrum) will remain unchanged.

As can be seen from formula (5), the first cause of out-of-band emissions noted above - the mutual shift in the envelope delay and the oscillations at the operating frequency - does not affect the harmonic composition (spectrum), the second reason is the distortion of the envelope when it is extracted (amplitude detection) and amplification - also does not take place, because the common-mode video-frequency (low-frequency) component and the quadrature video-frequency (low-frequency) component have a limited spectrum. For this reason, the total spectrum at the output of block 17 is also limited in frequency.

Schemes of output stages with two inputs and one output that perform the above functions are widely known in the scientific and technical literature, for example, in the books [5] and [7]. The use of multiplication blocks to isolate the video-frequency (low-frequency) components is also widely known, for example, in books [8] and [9].

Thus, the proposed method for transmitting a single-band signal can significantly reduce out-of-band emissions when operating in modes similar to class D with high efficiency.

Information sources

1. “Radio transmitting devices on semiconductor devices. Design and Calculation ./ Ed. R.A. Valitova I.A., Popova M., "Owls. Radio, 1973, p. 454.

2. Eric Gaalaas Class D Audio Amplifiers: What, Why, and How. Analog Dialogue J. http://www.analog.com/library/analog Dialogue / archives / 40-06 / class_d.html

3. David W. Cripe.], Improving the efficiency and reliability of AM broadcast transmitters through class-E power. http://www.bdcast.com/papers/amclasse.pdf

4. AM-500A 500 WATT AM-1A 1 KILOWATT AM BROADCAST TRANSMITTERS IM No.597-1112, October, 1999 webmaster@bdcast.com is available at: http://www.bdcast.com/fgal/prod_manual/AM500_1A_noschem_BCEPML. pdf Broadcast Electronics Inc. 4100 North 24th Street Quincy, IL 62305 Main telephone: (217) 224-9600 Main fax: (217) 224-9607 Webmaster e-mail

5. Verzunov M.V. “Single-band modulation in radio communications”, M., Military Publishing, 1972, pp. 246-257.

6. Gonorovsky I.S. "Radio-technical circuits and signals" Textbook for high schools, Ed.3-e, M., "Sov. the radio, 1977.

7. Levichev V.G. "Radio transmitting and receiving devices", Ed. 3rd, M., Military Publishing, 1974, p. 4.

8. Dickson R.K. "Broadband systems." Per. from English / Ed. V.I. Zhuravleva. - M., Communication, 1979.

9. Borisov V.I., Zinchuk V.M., Limarev A.E., Mukhin N.P., Shestopalov V.I. "Immunity of radio communication systems with the expansion of the spectrum of signals by the method of pseudo-random tuning of the operating frequency." - M., Radio and Communications, 2000.

Claims (1)

A method for transmitting a single-band signal, including supplying input information, according to which a signal is generated in one sideband (OBP signal), converting the generated OBP signal in two processing chains operating in parallel, and radiation into a radio channel, characterized in that they generate harmonic oscillation average radio frequency, as well as a harmonic signal with a constant amplitude at the middle frequency of the radio transmission; the first component of the OBP signal is formed in the first processing chain as follows: the OBP signal is multiplied with the harmonic voltage of the middle radio frequency, the first component of the video frequency is extracted from the received signal, which is the in-phase component of the OBP signal relative to the harmonic oscillation with the average radio frequency, then the first component of the video frequency is amplified and get the first control video voltage, while a harmonic signal with a constant amplitude at the middle frequency of the radio transmission amplify in terms of voltage, then at the same time they amplify in terms of power this voltage-amplified signal and change its amplitude according to the law of change of the first control video voltage; at the same time, in the second processing chain, the second component of the OBP signal is formed as follows: the OBP signal is multiplied with the harmonic voltage of the average radio frequency changed in phase by π / 2, the second component of the video frequency, which is the quadrature component of the OBP-, is extracted from the received signal signal relative to harmonic oscillations with an average radio frequency, then the second component of the video frequency is amplified and a second control video voltage is obtained, while the harmonic signal of the average frequency of the radio the drivers are phase-shifted by π / 2 and amplified by voltage, then they simultaneously amplify the power of this voltage-amplified signal and change its amplitude according to the law of variation of the second control video voltage; then the generated first and second components of the OBP signal are summed and the resulting output OBP signal is supplied for radiation to the radio channel.

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