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Lab. 9 Signal Analyzer
Signal/spectrum analyzer (SA): an equipment analyzing spectrum properties of signals.
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Type of SA:– Swept (downconvert one carrier at a time)
– Fourier (downconvert a band of carrier at a time)
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Swept analyzer:
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Resolution bandwidth:– The higher the resoultion, the slower the scan.
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Vector signal analyzer: – A SA that can conduct demodulation
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Fourier analyzer:
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7
Agilent approach:
Hardware
Software
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88
Software analyzer:– Analyze the signal recorded by hardware
Load recorded signal:– File Recall Recall demo (Help Signals) QPSK
Four windows (traces) are usually used:– Time constellation
– Spectrum
– EVM (time)
– EVM (average number) Find the length of the recoded signal:
– Window Player Find the properties of the recorded signal:
– Help Demo
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1010
1111
Use the label of each window to select what you want to see– Time
– IQ measurement
– Spectrum Use the unit of y-axis to have more selections Adjust the overlayed percentage:
– MeasSetup Frequency Time
– Change MaxOverlapp
– The higher the percentage, the slow the time sweep. Find out the demodulation properties:
– MeasSetup Digital demodulation properties
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Use markers:– Add markers from the command bar
– Marker Calculation select band power (set the center frequency and bandwidth)
– Can also use mouse to draw the band.
– Use OBW to select the band automatically. The connect used for general equipment is BNC and that
for RF transmission is SMA. For SA, we need to plug SMA into N type. We need some kind of connector transferring SMA to BNC.
The transmitter and receiver are not ideal in real-world. We have to give specifications for their performance so as to insure reliable communications.
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Analog/RF Impairments:– DAC
– Transmit IQ imbalance
– Phase noise of the mixer
– PA nonlinearity
– Channel effect
– Noise
– Receive IQ imbalance
– DC offset
– Phase noise of the mixer
– ADC
– Carrier frequency offset Digital processing:
– Precision (fixed-point processing)
– Receiver algorithms
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How to test/specify a communication system?– Transmitter/receiver performance (separated)
– Combine all impairments (combined) Transmitter:
– Transmit signal distortion (for receiver)
– Spectrum characteristic (for interference control) Indices for transmitter
– Error vector magnitude (EVM)
– Spectrum mask Index for receiver:
– Sensitivity
– Interference performance
* EVM is usually used for QAM signals.
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EVM: – A signal sent by an ideal transmitter would have all
constellation point at the ideal locations
– For real-world transmitter, however, the constellation points will deviate from the ideal locations in a random fashion.
– EVM is a measure of how far the constellation points are from the ideal locations
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2
1010)(
)(ˆ)(log
naE
nanaE EVM(dB)
%
)(
)(ˆ)(1002
2
naE
nanaEEVM(%)
* - 30dB~3.16% * - 40dB~1.00%
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Spectrum mask:– Confine the spectrum used for transmission (interference
control for the Bluetooth system)
20dB
20dB
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Practice 1:– Choose at least two kind of signals and analyze the
performance of the transmitters.