Electronics & Communication / QPSK I/Q Constellation
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LABORATORY 14 · ELECTRONICS & COMMUNICATION

Quadrature Phase Shift Keying (QPSK) I/Q Modulator Synthesis and Constellation Geometry

Implement a four-state QPSK modulator using orthogonal in-phase (I) and quadrature (Q) mixers, measuring constellation vector radius versus baseband drive voltage. Explore interactive telecommunication simulation, RF analysis, and signal processing telemetry.

ANALOG MODULATION · DIGITAL BASEBAND · PASSBAND MODULATION · ANTENNAS & RF · OPTICAL FIBER · DSP

Your virtual electronics & communication engineering laboratory.

CONSTELLATION SYMBOL VECTOR RADIUS R_SYM—
RF INSTRUMENTATION TELEMETRY

Ready to sample with I/Q Drive Voltage = 1.5 V.

1.5 V
Excitation locked to low-phase-noise synthesized reference oscillator.

Adjust I/Q Drive Voltage, then execute telecommunication RF/baseband acquisition.

Communication telemetry is sampled with calibrated high-precision instruments using 64-bit IEEE 754 precision buffers. Residuals reflect ordinary least-squares regression across successive observations. Continuous data structures support high-fidelity modulation, channel, and spectral analysis.

Communication engineering assumptions and boundary limits

Channel modeled under additive white Gaussian noise (AWGN) and linear band-limited propagation. Harmonic distortion remains constrained below -45 dBc across all calibrated test points.

Laboratory apparatus & testing equipment.

QPSK I/Q Constellation Telecommunication Workstation

Provides regulated RF/baseband excitation, precision impedance-matched test fixtures, and low-noise interconnection for two bits per symbol spectral efficiency, gray coding & phase jitter trajectories.

6.5-Digit True-RMS Digital Multimeter (Keysight / Fluke)

Measures DC bias points, RMS carrier/signal voltages, and circuit node potentials with ±0.0035% baseline accuracy.

Four-Channel Digital Storage Oscilloscope (200 MHz, 2 GSa/s)

Captures high-frequency RF envelopes, baseband eye diagrams, constellation patterns, and transient responses for qpsk i/q constellation.

Synthesized Vector RF Signal Generator (9 kHz – 3 GHz)

Delivers calibrated, low-phase-noise continuous-wave and modulated carrier signals to establish i/q drive voltage conditions.

High-Dynamic-Range RF Spectrum Analyzer (9 kHz – 3.6 GHz)

Quantifies fundamental harmonic amplitudes, carrier suppression ratios, sideband power distributions, and spurious emissions.

Matched 50-Ohm Coaxial Interconnects & Attenuator Set

Maintains uniform transmission line impedance, eliminates unwanted standing-wave reflections, and protects instrument front-ends.

FOLLOW THE METHOD

A reason behind every step.

Implement a four-state QPSK modulator using orthogonal in-phase (I) and quadrature (Q) mixers, measuring constellation vector radius versus baseband drive voltage. Standardized parameter settings: 0.5, 0.9, 1.3, 1.7, 2.1, 2.5 V.

  1. Apparatus Calibration & Ground Plane Verification: Inspect all coaxial BNC/SMA interconnects and verify 50-ohm characteristic termination. Power up all instruments and allow a 20-minute thermal settling period to stabilize crystal reference oscillators.
  2. Carrier & Modulating Signal Synthesis: Configure the synthesized RF signal generator and baseband source to the specified baseline parameters. Calibrate the i/q drive voltage using the precision digital multimeter and oscilloscope.
  3. Systematic Telemetry Acquisition & Setpoint Stepping: Increment the i/q drive voltage systematically across the experimental range (0.5 to 2.5 V), logging the resulting constellation symbol vector radius r_sym after signal settling.
  4. Frequency-Domain & Time-Domain Cross-Validation: Observe and photograph the corresponding waveform on the digital storage oscilloscope and verify the spectral distribution on the RF spectrum analyzer. Verify that harmonic distortion remains below -45 dBc.
  5. Repeatability & Hysteresis Verification: Execute both ascending and descending parameter sweeps across the device under test (DUT) to detect any thermal drift, detector non-linearity, or oscillator pulling.
  6. De-energization & Dataset Archival: Safely reduce RF excitation levels, save captured digital waveforms to non-volatile storage, export telemetry to the laboratory logbook, and power down all high-frequency instrumentation.
YOUR NOTEBOOK · 0 OBSERVATIONS

Turn measurements into telecommunication engineering insight.

See a complete example report ↗

Points are your recorded observations. The solid regression line validates QPSK I/Q Constellation mathematical scaling.

LINEAR REGRESSION FIT · y = mx + b
r_sym = 1.4142 · V_IQ
#Baseband I/Q Drive Voltage V_IQ (V)Constellation Symbol Vector Radius r_sym (V)Baseband I/Q drive voltage V_IQ (V)Symbol vector radius r_sym (V)

No readings yet. Execute a communication trial and record it.

CHECK YOUR UNDERSTANDING

Explain what the communication metrics mean.

Question 1: In the experimental investigation of QPSK I/Q Constellation, the primary dependent variable measured is:

Question 2: The mathematical relationship governing QPSK I/Q Constellation is modeled as:

Question 3: The target benchmark parameter derived from regression analysis is:

Question 4: Which instrument provides the most accurate visualization of spectral harmonics and carrier sidebands in the frequency domain?

THEORY AND ELECTROMAGNETIC CONTEXT

Electronics & Communication Engineering background & physical principles.

Implement a four-state QPSK modulator using orthogonal in-phase (I) and quadrature (Q) mixers, measuring constellation vector radius versus baseband drive voltage.

r_sym = 1.4142 · V_IQ

Communication systems rely on Fourier spectral decomposition, Shannon channel capacity, and electromagnetic propagation theory.