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Lab Report
Radio Engineering-Ⅱ
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Contents
1.
TRANSMITTER DESIGN ................................................................................. 3
1.1. π/4 – DQPSK Modulation method ............................................................ 3
1.2. Raised cosine filter and pulse shaping: ..................................................... 3
1.3. Adjacent channel power ratio (ACPR) ...................................................... 4
1.4. Back off ..................................................................................................... 5
1.5. Simulation result ........................................................................................ 6
1.6. Questions ................................................................................................... 9
1.7. Error vector and EVM calculation .......................................................... 10
2.
RECEIVER DESIGN ....................................................................................... 12
2.1. Super-heterodyne Receiver Principle ....................................................... 12
2.2. Design specification ................................................................................ 13
2.3. Parameters ............................................................................................... 13
2.4. Selection of IF Frequency ....................................................................... 14
2.5. RF Filters ................................................................................................. 16
2.6. Low Noise Amplifier ............................................................................... 16
2.7. Mixer and Local Oscillator ...................................................................... 17
2.8. IF filter ..................................................................................................... 18
2.9. IF Amplifiers ........................................................................................... 18
3.
SIMULATION AND RESULT ........................................................................ 19
3.1. Budget Analysis and result ...................................................................... 19
3.2. Spurious Response Simulation ................................................................ 19
3.3. Third order Intercept................................................................................ 20
4.
REFERENCES .............................. ERROR! BOOKMARK NOT DEFINED.
5.
DATASHEET ................................................................................................... 22
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1.
TRANSMITTER DESIGN
In radio communication system, transmitter is a device is to cooperate with antenna
to propagate radio waves. The transmitter which generates radio frequencies and
applied to the antenna.
In this lab work, design work must be done by following a given specifications.
Which determines this project will be operated in a telecommunication system. The
given specifications are Modulation method 𝜋/4- DQPSK
 Data rate 32 Mbit/s
 Center frequency of the system tuning range 10GHz
 Bandwidth of the main lobe between first nulls of the pulse shaped signal
20MHz
 Transmitter uses square-root raised cosine pulse shaping with the roll-off
factor α
 The system has 15 channels
The performance criteria that the transmitter should met is given as ACPR of the transmitted signal must be at least –52 dBc in the channels
adjacent to the main channel (ACPR is measured by integrating the power
density over the bandwidth of the channel)
 Power of the useful signal must be at least +9 dBm
 The rms-value of the error vector (EVM) must be under 5 %

1.1.
π/4 – DQPSK Modulation method
π/4 – DQPSK Modulation method considered as the superposition of two QPSK
signal constellations creating eight phases having 45 degrees offset.
Symbol phases are selected in an alternative way from one of the QPSK
constellations. Therefore, successive symbols have relative phase difference with one
of four angles +/- n /4 and +/- 3n /4.
It can be implemented by low complexity receiver structure which is the advantage
of differential detection process. It is a compromise between QPSK and Offset-keyed
QPSK (OKQPSK) as it has a maximum phase change of 135 degrees compared to 180
degrees for QPSK and 90 degrees for OKQPSK.
1.2. Raised cosine filter and pulse shaping:
Pulse shaping is used to shape the spectrum of the signals. In wireless
communication, pulse shaping is essential to limit output spectral density of the
modulator. Shaping reduces the sidelobe energy relative to a rectangular pulse so as to
reduce the intersymbol interference (ISI) between pulses in the received signal. Thus,
it changes the waveform of the transmitted signals by limiting the effective bandwidth
of the transmission so as to fit into the modulator output spectral density limit.
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The effective pulse shape satisfying the Nyquist criterion can reduce the ISI. For
the best result raised cosine pulses are used as it satisfies the Nyquist criteria the
effectively.
Frequency response of the raised cosine filter in frequency domain is given by:
In our design exercise, data rate of the system is 250 Kbps and bandwidth of each
channel is 200 KHz.
Now, to calculate the roll off factor, we have bandwidth,
B=(1+α) Rs,
where Rs = 1/Ts
The number of bits in n/4-DQPSK modulation is 2. So,
Rs = 32/2 Mbit/s
= 16 Mbit/s
Here, bandwidthB= 20 MHz
Roll off factor (α) = (20MHz/16Mbit/s) -1
= 0.25
1.3. Adjacent channel power ratio (ACPR)
Adjacent power ratio is a measure of the degree of signal spreading. It is defined as
the power contained in a defined bandwidth (BR) at a defined frequency (fR) [or defined
offset frequency from the channel center frequency (fT)], divided by the power in a
defined bandwidth (BT) placed around the channel center frequency. The two
bandwidths BT and BR need not be the same. It is defined as the power ratio between
the total power of adjacent channel to the main channel´s power. It can also be defined
as the ratio of the output power around the center of carrier to the power in the adjacent
channel.
Measuring ACPR have two different ways, the first way is by finding 10*log of the
ratio of the total Output power to the power in adjacent channel. And the second is to
find the smaller bandwidth with smaller output power nearby center of carrier to the
in the adjacent channel.
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Figure 1: ACPR
1.4. Back off
The level of a signal at the input of an amplifier relative to that level at the input that
would result in the maximum possible output level. It is used to describe the operating
point. Small values of back-off caused by amplitude saturation are substantially large.
Increasing amount of back-off decreases efficiency significantly.
Figure 2: Back Off Output.
Our task is to design a transmitter with, the ACPR of the transmitted signal specified
to be at least -52 dBc in the channels adjacent to the main channel (ACPR is measured
by integrating the power density over the bandwidth of the channel) with the power of
the transmitter signal to be at least +9 dBm
The RF frequency given is 10 GHz in our case, the roll-off factor,(calculated above
is 0.25) symbol rate of 16 Mbps, Bandwidth of the main lobe between first nulls of
the pulse shaped signal to be 20 MHz and other parameter values are set to the
schematic. Iteratively the simulation work is performed to ensure the fulfillment of
the requirements specified. The output power region specifying the linear zone for the
amplifier is defined by 1 dB compression points and operating intersecting point
OIP3. Thus ACPR is affected by 1dB compression point and OIP3.
When the output power is near the 1dB compression point, ACPR is decreased due
to the increment of the nonlinear behavior of the amplifier. With the given constraints,
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we have selected LNA-20-00104000-75-15P Transmitter amplifier for our design
work. Which is unconditionally stable with 50 ohm input and output match, internally
regulated. The given model and the specification matches with our chosen model
which works well.
Name
Frequency Range
Maximum Gain
Noise Figure
LNA-20-00104000-75-10P
0.1-40 GHz
20 dB
7.5 dB
15 dBm
1dB compression Point
Table 1: Transmitter Specifications
1.5. Simulation result
Figure 3: Amp. ACPR, Constellation & EVM simulation
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Figure 4: Envelope & VAR
Figure 5: Transmitted Spectrum and Trajectory Diagram
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Figure 6: ACPR power gain calculation results
Figure 7: Results ACPR power calculations
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Figure 8: Received Spectrum showing upper lower and main spectrum
Figure 3 to Figure 8 illustrates the value of ACPR comparing to the specification
meets the gain of +8.901 almost +9dBm which satisfy the requirement, ACPR is found
-70.479dBm for lower channel ACPR and -71.542dBm for upper channel ACPR.
Due to the effect of the non-linearity property of amplifier, from the received power
spectrum, higher signal power is at the center frequency of the side lobes is noticeable.
The Adjacent channel carrier noise and IM distortion caused by amplifier causes
distorted waveform spectrum. By controlling amplifier power IM distortion could be
reduced on the other hand power link expenses for it.
So, there is a tradeoff in between these two parameters. Increasing the amplifier
output power, the amplifier can be brought under the saturation region but with the
increase in input power nonlinearity of the amplifier is increased thereby increasing
the ACPR.
1.6. Questions
What do you notice and what causes the difference between the transmitted
and received signal?
Signal spectrum causes distortion before filtering accurately which creating the
difference between the transmitted and received signal. Pulse shaping done at the
transmitter and receiver half causes the desired bandwidth to be utilized and attenuated
the remaining to retain the power of information signal and causes decrease in the
ACPR.
What is the value of the back-off needed at the power amplifier in order to
fulfill the requirement?
Back off = output power at 1dB compression point-gain available power source
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=15-20-(-13)
=8dBm
1.7. Error vector and EVM calculation
The error vector describes the deviation of the transmitted signal from the ideal
signal. Correctness of the transmitted signal can be described from error vector.
The error vector magnitude is the length of the vector—at the detected symbol
location—which connects the I/Q reference-signal vector to the I/Q measured-signal
vector. The following graphic shows the calculation of the EVM metric as well as a
diagram showing how a single error vector is calculated.
1
𝑁
2
2
√( ∑𝑁−1
𝑛=0 𝐼𝑒𝑟𝑟 [𝑛] +𝑄𝑒𝑟𝑟 [𝑛]
%𝐸𝑉𝑀 = 𝐸𝑉𝑀 𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒*100%
Where,
n= Symbol index
N= Number of symbols
Ierr = IRef - IMeas
Qerr= QRef- QMeas
EVM is calculated from the symbol points (the instant in time when symbols are
detected). The computation does not include points between symbols. Therefore Points
/ Symbol does not affect the value. The Syms/Errs table also shows the location of the
symbol that has the largest EVM.
For Offset QPSK, when the Half Sine Filter is selected, the OQPSK reference
constellation points fall on a circle with a magnitude of sqrt(2)/2, but the EVM is still
expressed as a percentage of the magnitude of a QPSK symbol point (magnitude = 1).
A Surface Acoustic Wave (SAW) filter is a filter which is used to calculate the EVM
that converts the electrical input signal to an acoustic wave. It consists of interleaved
metal electrodes to transmit and receive the waves, so that an electrical signal is
converted to an acoustic wave and then back to an electrical signal. There are various
types of SAW filter offering the advantageous factor like low shape factor small size,
or high-frequency operation. The stop band level is limited by the device’s ability to
dampen undesired vibrations.
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Figure 9: EVM Results
The ideal and distorted signal shows the error vector magnitude clearly in Figure
9. . Here to avoid the delay difference between the measurement path and the reference
path, a delay element with a group delay of 1 ms is added to the reference. From above
Figure with the input specific power the error vector percentage was below 5 %
(4.839%) which satisfies the requirement.
Define how steep the SAW-filter may be that the rms-value of the error vector
id below 5 %. i.e. what is the limit for the shape factor (BW-60dB/BW-3dB,
BW=bandwidth) of the SAW-filter that the performance criteria is fulfilled?
Error vector magnitude EVM= 4.839%
Stop band frequency, BWstop =42 MHz
Pass band frequency BWpass=20 MHz,
Then the performance is fulfilled when, shape factor which is given by the ratio
of Stop band frequency and Pass band frequency (BW-60dB/BW-3dB) is=42/20 MHz
=2.1
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2.
2.1.
RECEIVER DESIGN
Super-heterodyne Receiver Principle
The super-heterodyne radio is defined by the mixing of the received signal with
locally generated signal (Local Oscillator signal) to generate new signals at desired
intermediate frequency (IF) through the process of heterodyning. The newly generated
signals pass through various filtering and amplifying stages.
Tuning is achieved by varying the frequency of the local oscillator as it allows
processing of only desired fixed frequencies. The IF frequency is generally selected at
lower frequency than incoming signal to enhance the performance of radio receiver
and reduce its cost.
The main incoming signal first enters the front end band pass filter responsible for
removing the image signal and often followed by RF amplifier to amplify the signal
before entering the mixer. The tuned and amplified signal enters the mixer stage. The
incoming signal is mixed with a local oscillator signal to produce sum and difference
frequency components. After the mixing operation the new IF signal enters the IF
processing stages. The signal is amplified in several IF- amplifier stages which
provides most of the gain to desired signal.
Figure 10: Receiver Architructure
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2.2. Design specification
The receiver is designed to meet the below given specificationsModulation
π/4-DQPSK
Data rate
32 Mbit/s
Center frequency of the system
10 GHz
20 MHz
Bandwidth of the main lobe between
first nulls
of the pulse shaped signal
Channels
15 (RF tuning range 9.85...10.15 GHz)
Sensitivity
at least –87 dBm
SNR requirement at the output of the
at least +9dB
IF-stage
Signal level at the output of the IF-stage at least +3 dBm
the 1 dB compression point
greater than +19 dBm
Spurious responses
Less than -70 dBm.
Maximum level for the input signals causing
spurious responses is -20 dBm.
OIP3
At least +9 dBm.
Two input signals both at level -40 dBm
The frequency of the first signal is 10 MHz and
the frequency of the second signal is 20 MHz
away from the carrier frequency so that they
both are located on the same side in frequency
Band in respect to the carrier frequency.
Table 2: Receiver Specification
2.3. Parameters
Receiver Sensitivity is a key specification in determining the performance of
receiver. It is the minimum input signal required to produce acceptable output signal
having specified signal to noise ratio (SNR). The main requirements of any radio
receivers include the ability to separate each station from one another by the RF section
i.e. selectivity and also the signals should be sufficiently amplified so that the signal
level is high enough to extract the original information.
Noise Figure is one of the most widely used parameter to determine the sensitivity
of the receiver. It is based on the fact that limitation on the sensitivity of a radio
receiver is not the level of amplification but the level of overall noise present. Noise
Figure (NF) can be determined as,
NF = INPUT SNR – OUTPUT SNR
Where,
INPUT SNR= Receiver's input signal-to-noise ratio
OUTPUT SNR= receiver’s output signal-to-noise ratio
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(Given in specification as SNR requirement at the output of the IF-stage)
The thermal noise floor given by,
Pn = kTB
Where,
k= Boltzmann constant
T= Noise temperature
B is equivalent noise Bandwidth given by
bandwidth of IF Filter
So, the noise power isPn = -174dBm/Hz+10𝒍𝒐𝒈𝟏𝟎 (𝟐𝟎𝑴𝑯𝒛)
Pn = -101dBm
The Receiver Noise Figure can be calculated using sensitivity and thermal noise
floor is,
NF = Sensitivity – Pn – SNR OUT
NF = –87 + 101 – 9
NF = 5 dB
Now, total gain can be determined as,
Gain= Required IF output signal level- Sensitivity
Gain= 3dB+87 dB =90dB
The systems requires above calculated Noise Figure and overall Gain at the output
of IF stage to maintain the desired QOS.
2.4. Selection of IF Frequency
An intermediate frequency (IF) is a frequency to which an incoming carrier
frequency is shifted as an intermediate step in transmission or reception. The
intermediate frequency is created by heterodyning, resulting in a signal at the sum and
difference of two input signals as an essential task before amplification and detection.
Translation of carrier frequency to lower intermediate frequency has several
advantages in processing the signal.
At very high frequencies, amplifier is unable to operate in linear region hence
cannot deliver much amplification. One crucial advantage of using intermediate
frequency is to improve frequency selectivity. Front end band pass filter can only reject
the signals well separated in frequency but IF part should be able to extract out signals
or components of signal close enough in frequency. The IF needs to separate out the
each 15 channels
The selection of an appropriate IF in a heterodyne transceiver affects the entire
performance of heterodyne receiver. The primary consideration in the choice of the IF
is the attenuation of image frequency. It is observed that the image frequency is a major
source of unwanted interference in any heterodyne receiver. Other considerations
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while selecting IF are local oscillator radiation towards antenna and rejection of
spurious responses.
Figure 11: Image Frequency
The mixer is a three port device operating in the non-linear region and non-linearity
characteristics being responsible for generation of various new frequencies at the
output of mixer.
For given intermediate frequency (fIF), carrier center frequency (fRF), local
oscillator frequency (fRF) at the mixer output is given by the equation,
fLO = fRF + fIF
In this design we consider a down converter mixer such that the difference of fRF
and fLO is used to determine the fIF. Further we consider High Side Injection the fLO is
higher than fRF.
Hence the mixer can be represented as High Side Downconverter.
The image frequency is given by,
fimg = fRF + 2fIF
The undesired image frequency components have to be taken in account in the IF
selection process as image signal in the nearby frequency band may have much
stronger power than a weak signal in desired band.
Based on IF filters frequency, IF center frequency of 618 MHz was used because
operating at the lower IF frequency is generally desirable because signal processing
performs better at lower frequency providing wider choice and lower cost of IF filters.
Also the layout of the IF stage is less critical and it is easier to achieve high gain
without having oscillation problem.
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2.5. RF Filters
RF filters are the front end band pass filter and RF stage is responsible for
broadband tuning. The tuning range parameters are as follows:
Center Frequency
10 GHz
Total Channel
15
20 MHz
Bandwidth of the main lobe
between first nulls of the pulse
shaped signal
Overall Bandwidth
300 MHz
Overall Tuning Range
10 +/- 0.15GHz
Table 3: RF Tuning range
In heterodyne radio receivers band-pass pre-selection filters need to reject the
signals on the image frequency and any harmonic components of the RF frequency.
Although selectivity is not high at this stage, it needs to prevent the strong undesired
channel signals from entering and overloading the receiver particularly in later stages
such as RF amplifier and mixer.
The image frequency in case of high side injection is given by
fimg = fRF + 2fIF
fimg range =9.85 GHz ~ (10 GHz) ~ 10.15Hz =300MHz
As RF filter is the first component in the cascade of radio receiver chain, it has the
highest contribution to the overall noise figure of the system. The RF filter should have
minimum possible noise figure and sufficiently sharp to reduce the image responses to
acceptable level.
The specifications of the chosen RF filter are presented in table below,
Name
Center Frequency
Passband Bandwidth
Passband Attenuation
Stopband Bandwidth
Stopband Attenuation
Insertion Loss
5FV20-10000-T300-SM-SM
10 GHz
333MHz
1 dB
600 MHz
30.033 dB
1.43 dB
Table 4: RF Filter Parameters
2.6. Low Noise Amplifier
Low Noise Amplifier is the first component of RF section. It is used to reduce the
spurious responses, inter modulation and cross modulation keeping the comparatively
low amplification levels.
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So LNA amplifier is good to keep right after the pre selection RF filter in the design
work. The noise factor of an LNA is preferred to be small as it has a significant effect
on the total noise figure. If the spurious response is not rejected enough in this section,
desired result can be further obtained by adjusting the gain of RF amplifier.
The parametric values are along with the LNA is shown in the table below:
Name
Frequency Range
Maximum Gain
Noise Figure
LNA-20-08001200-09-10P
8-12 GHz
20 dB
0.9 dB
10 dBm
1dB compression Point
Table 5: Low Noise Amplifier Parameters
2.7. Mixer and Local Oscillator
Mixers are basically used to convert RF frequency to intermediate frequency. It is
a nonlinear electrical circuit that creates new frequencies from the signals applied to it
each containing the modulation contained in the desired signal. For the frequencies f1
and f2 applied to a mixer, it generates the new signals at the sum f1 + f2 and difference
f1 - f2 of the original frequencies.
Mixers are used for heterodyning the signals i.e. shifting the signals from one
frequency range to another. For this the local oscillator creates a frequency for mixing
the incoming signal with the LO signal to get the intermediate frequency.
The design work requires the mixer with the parameters LO signal level, operational
frequency range, conversion loss, OIP3 performance and noise figure. Other
parameters are isolation between ports and spurious responses.
The local oscillator frequency is 10.618 GHz and the radio frequency range of 9.85
GHz -10.15GHz with a center frequency of 10 GHz to generate the corresponding
intermediate frequency with respect to its RF and LO frequency.
The different parameters of the mixer and local oscillator and their values are listed
in the table below:
Name
Bandwidth
Conversion Gain
Noise Figure
LO frequency
LO power
LO_Rej1(LO-RF isolation)
LO_Rej2(LO-IF isolation)
DB0418LW6
4 to 18 GHz
8 dB
7.5 dB
10.618 GHz
16 dB
25 dB
20 dB
Table 6: Mixer Parameters
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2.8. IF filter
IF filter is the filter that selects the intermediate frequency, created by mixing the
carrier signal with a local oscillator signal, also known as heterodyne principle to
which a carrier frequency is shifted as an intermediate step in signal transmission or
reception. We require an IF filter with band pass bandwidth of 300 MHz so that each
channel is allocated 20 MHz bandwidth. The center frequency used is 618 MHz. It
attenuates the spurious responses created in the mixer.
The low IF values is good for achieving the higher selectivity. This selectivity refers
to an ability to reject the adjacent signals.
Name
Center Frequency
Passband Bandwidth
Passband Attenuation
Stopband Bandwidth
Stopband Attenuation
Insertion Loss
3DH35-618-T20-1.9
618 MHz
22.2Hz
3 dB
600 MHz
25.29 dB
1.9 dB
Table 7: IF filter Parameters
2.9.
IF Amplifiers
The IF amplifier provides the highest signal level amplified by the previous
amplifiers in the circuit arrangement. It is very important that the total amplification
of a super heterodyne receiver is divided between RF stage amplifier and IF stage
amplifier. This scheme provides the most of the gain in the receiver. IF is regarded as
having high gain, often multistage, single-frequency tuned radio frequency amplifier.
So, to reduce the inter modulation distortion and to reduce the unwanted spurious
responses, most of the gain is placed after IF filtering.
The properties of the different IF amplifiers used are presented in table below.
Parameters
NSME-00100400-1410P-4
Frequency Range 0.1-4GHz
LNA-20-02001200-1810P
2-12GHz
Maximum Gain 24 dB
Noise Figure
1.4 dB
1dB compression 10
Point
20
1.8
10
Table 6: IF Amplifier Parameters
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3.
SIMULATION AND RESULT
3.1. Budget Analysis and result
Figure 12: Receiver design for Budget Analysis
Figure 13: Schematic for Budget Simulation and corresponding data file
3.2. Spurious Response Simulation
The effect of undesired high power spurious responses that are near the frequency
band of desired signal are in focus. The simulation for the measurement of spurious
response is shown below,
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Figure 14: Schematic for Spurious Responses
Figure 15: Spurious Response (image frequency)
3.3. Third order Intercept
Third Order Intercept (TOI) simulation is performed to focus on the tolerance of
the receiver against the inter modulation products generated at the non-linear stages of
the receiver chain. The mixer output consists of various unwanted responses at various
frequency bands due to combining of two signals.
The inter modulation products appear not only at the sum and difference of fLO and
fRF but also at their multiples. The levels of inter modulation products can be evaluated
using intercept points of different inter modulation products. The simulation is
performed by disabling the IF filter and measuring OIP3 from the mixer's output as
shown in schematic. The parameters were set as shown below,
RF frequency= 10 GHz
LO frequency= 10.618 GHz
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RF power= -40dBm
Figure 16: Third Order Intercept Schematic
For 10 MHz,
Figure 17: Third Order Intercept for 10 MHz
For 20 MHz,
Figure 18: Third Order Intercept for 20 MHz
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4.
DATASHEET
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