Lab 1: Modulation Zoo — GNU Radio Constellation and Spectrum Capture

Chapter: 1 (Weeks 1-2) Duration: 2 hr in-class + 1 hr independent Substrate: GNU Radio (software-only for Part 1; ANTSDR E200 optional for Part 2) Points: 8

Overview

Build GNU Radio flowgraphs for all seven modulation schemes covered in Weeks 1-2. Capture constellation diagrams and spectrum plots for each. No hardware required for Part 1 (software simulation). Part 2 optionally uses the ANTSDR E200 for hardware observation.

Part 1: Software Simulation (2 hr)

Build each modulation flowgraph using GNU Radio Companion. For each, capture screenshots of:

1. QT GUI Frequency Sink (spectrum)
2. QT GUI Constellation Sink (IQ scatter)
3. QT GUI Time Sink (time domain, optional)

1.1 OOK (On-Off Keying / ASK)

[Bernoulli Binary Source]
      |
   [Float to Char]
      |
   [Chunks to Symbols]   (symbol map: [0.0, 1.0])
      |
[Repeat] (samples_per_symbol=8)
      |
[Float to Complex]
      |
[Signal Source] -----> [Multiply] ----> [Throttle] ----> [QT GUI Frequency Sink]
(sine, 1kHz, 0-phase)                               ----> [QT GUI Constellation Sink]

Sample rate: 32000. Symbol rate: 4000. Carrier: 1000 Hz.

1.2 BPSK

[Bernoulli Binary Source, bits_per_symbol=1]
      |
   [BPSK Mod] (samples_per_symbol=4)
      |
   [Channel Model] (noise_voltage=0.1, optional)
      |
   [Throttle]
      |
   [QT GUI Frequency Sink + Constellation Sink]

1.3 QPSK

Same as BPSK but use [QPSK Mod] (bits_per_symbol=2). Observe: four clusters in the constellation instead of two. Spectrum bandwidth: same as BPSK (same symbol rate, 2× data rate).

1.4 16-QAM

[Bernoulli Binary Source, bits_per_symbol=4]
      |
   [QAM Mod] (constellation_size=16)
      |
   [Throttle]
      |
   [QT GUI Constellation Sink]

1.5 GFSK

[Bernoulli Binary Source]
      |
   [GFSK Mod] (samples_per_symbol=4, sensitivity=0.3, bt=0.35)
      |
   [Throttle]
      |
   [QT GUI Frequency Sink + Constellation Sink]

Compare GFSK spectrum to BPSK spectrum at the same symbol rate. GFSK bandwidth is wider (FM-family vs. PM-family).

1.6 WBFM (Wide-Band FM, analog)

[Signal Source] (sine, 300 Hz, audio frequency)
      |
   [WBFM Transmit] (quadrature_rate=48000, deviation=75000)
      |
   [Multiply Const] (0.3)
      |
   [Throttle]
      |
   [QT GUI Frequency Sink]

Observe: wide spectral spreading, characteristic double-hump spectrum.

1.7 AM-DSB

[Signal Source] (sine, 1 kHz, amplitude 0.5)  →  [Add] → [Multiply] → [Throttle] → [Frequency Sink]
[Const Source] (1.0)                           ↗           ↑
                                                   [Signal Source] (sine, f_carrier=5000 Hz, amplitude 1.0)

Observe: two sidebands symmetric around the carrier; no carrier suppression (DSB-LC = double-sideband large carrier).

Part 2: Hardware Observation (optional; ANTSDR E200 required)

Use the ANTSDR E200 in loopback mode (TX → RF cable → RX, or TX → Faraday-cage RX) to observe each modulation on actual hardware.

TX flowgraph: Signal Source / GFSK Mod / BPSK Mod → PlutoSDR Sink (URI: ip:192.168.1.10, TX freq: 433.5 MHz, TX gain: 0 dB)

RX flowgraph: PlutoSDR Source (same URI, RX freq: 433.5 MHz, sample rate: 2 MSPS) → QT GUI Frequency Sink + QT GUI Constellation Sink

Capture: screenshot of hardware-received constellation for BPSK and GFSK. Compare to software simulation.

Virtual path (no hardware): The software simulation flowgraphs from Part 1 are the virtual-path deliverable. Add Channel Model block with noise_voltage=0.1 to simulate a real-world noisy channel.

Deliverables

• 7 frequency-sink screenshots (one per modulation)
• 7 constellation screenshots (one per modulation)
• 1 paragraph per modulation: what does the constellation and spectrum tell you about this modulation scheme?
• Comparison table: fill in bandwidth, noise robustness (qualitative), and receiver complexity for each scheme

Grading (8 points)