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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.

55

Vector signal analyzer: – A SA that can conduct demodulation

6

Fourier analyzer:

6

7

Agilent approach:

Hardware

Software

7

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

99

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

1212

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

2

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.