Lab 11: ANTSDR E200 Advanced Full-Duplex IQ

Chapter: 7b (Week 9) Duration: 4 hr Substrate: ANTSDR E200 (mandatory; see lab-server scheduling for remote students) Points: 10

Overview

Use the ANTSDR E200 in full-duplex mode to simultaneously transmit and receive IQ at different frequencies. Build a complete gr-iio GNU Radio pipeline from scratch. This lab requires physical or lab-server access to the ANTSDR E200.

Remote students without direct E200 access: Contact the instructor to schedule lab-server E200 time. The lab server exposes the E200 via the IIO network context at ip:<server-address>. Connect your GNU Radio instance to ip:<server> instead of ip:192.168.1.10.

Part 1: ANTSDR E200 Smoke Test (30 min)

Verify the E200 is reachable and functional:

# Network connectivity
ping -c 3 192.168.1.10

# IIO device discovery
iio_info -u "ip:192.168.1.10"
# Expect: iio:device0 = ad9361-phy; iio:device1 = cf-ad9361-lpc (RX DMA); iio:device2 = cf-ad9361-dds-core-lpc (TX)

# Read AD9361 hardware parameters
iio_attr -u "ip:192.168.1.10" -c ad9361-phy voltage0 sampling_frequency
# Returns current sample rate

# Set RX frequency to 433.92 MHz via CLI
iio_attr -u "ip:192.168.1.10" -c ad9361-phy altvoltage0 frequency 433920000

Part 2: RX-Only Flowgraph (45 min)

Build a simple receive-only flowgraph using the PlutoSDR Source block (gr-iio):

[PlutoSDR Source]
  URI: ip:192.168.1.10
  Frequency: 433.92e6
  Sample Rate: 2e6
  RF Bandwidth: 2e6
  Buffer size: 32768
  Gain: Manual, 40 dB
      |
   [DC Blocker] (length=32)
      |
   [Low Pass Filter]
     (cutoff=200e3, transition=50e3, sample_rate=2e6)
      |
   [QT GUI Frequency Sink]
     (center_freq=433.92e6, bandwidth=2e6, ref=-60, y_per_div=10)
      |
   [QT GUI Waterfall Sink]
     (center_freq=433.92e6, bandwidth=2e6)

Run the flowgraph. You should see the 433 MHz ISM band in the spectrum and waterfall displays. Tune to any active signal you can see.

Capture 10 seconds to file:

Add a File Sink block after the LPF. Record antsdr-rx-433.iq (10 seconds at 2 MSPS = 80 MB as complex64).

Part 3: TX-Only Flowgraph (45 min)

RF-shielded enclosure required. Do not operate transmit flowgraph without the Faraday cage.

Build a transmit-only flowgraph:

[Signal Source]
  Waveform: Sine
  Frequency: 100e3 (100 kHz offset from TX centre)
  Amplitude: 0.5
      |
   [Multiply Const] (0.5)
      |
[PlutoSDR Sink]
  URI: ip:192.168.1.10
  Frequency: 433.5e6   (500 kHz offset from 433.92 MHz; stay within ISM band)
  Sample Rate: 1e6
  RF Bandwidth: 1e6
  Attenuation: 60 dB   (low power; in shielded enclosure)
  Buffer size: 32768

Verify: on a separate receive flowgraph (RTL-SDR or second ANTSDR E200 context), confirm the tone is visible at 433.5 + 0.1 = 433.6 MHz.

Part 4: Full-Duplex Loopback (60 min)

Connect TX output to RX input via a short coaxial cable + 30 dB attenuator (or use the RF shielded test enclosure's TX/RX ports). Run TX and RX simultaneously in one flowgraph:

[Signal Source (100kHz sine)] → [PlutoSDR Sink]  (TX @ 433.5 MHz, atten=40 dB)

[PlutoSDR Source] (RX @ 433.5 MHz, gain=30 dB, SR=2 MSPS) → [DC Blocker] → [Low Pass Filter] → [QT GUI Frequency Sink]

The same GNU Radio flow graph can connect to both TX and RX contexts of the same E200. Both PlutoSDR Source and PlutoSDR Sink use ip:192.168.1.10.

Observation: You should see your transmitted CW tone at +100 kHz in the RX spectrum display. The loopback path through the cable + attenuator confirms TX and RX are both functional.

Measure TX-to-RX isolation: Vary the TX attenuation (PlutoSDR Sink attenuation parameter) in steps (30/40/50/60 dB). For each, record the received tone amplitude from the QT GUI Frequency Sink. Plot: TX attenuation vs. RX signal level.

# Expected relationship: RX_level(dBm) = TX_power(dBm) - cable_attenuation(dB) - TX_atten_setting(dB) + RX_gain(dB)
# Solve for cable_attenuation from your measurements

Part 5: Custom OOK Transmitter (30 min)

Replace the CW Signal Source with an OOK modulated signal:

[Bernoulli Binary Source] → [Repeat (8 samples/bit)] → [Float to Complex]
                                                               |
                                                        [PlutoSDR Sink] (TX @ 433.5 MHz)

On the RX side, add: Low Pass Filter → Complex to Real → Binary Slicer → File Sink (rx_bits.bin).

Verify that transmitted bits are recovered correctly:

import numpy as np
# tx_bits and rx_bits should match (after accounting for delay)
tx_bits = np.fromfile("tx_bits.bin", dtype=np.float32)
rx_bits = np.fromfile("rx_bits.bin", dtype=np.float32)
delay = 20  # samples; adjust
match_rate = (tx_bits[delay:len(rx_bits)+delay] == rx_bits[:len(tx_bits)-delay]).mean()
print(f"Loopback bit accuracy: {match_rate*100:.1f}%")
# Expect > 95% for clean loopback

Deliverables

• ANTSDR E200 smoke test output (iio_info output, first 10 lines)
• RX flowgraph screenshot + spectrum screenshot showing an ISM-band signal
• TX flowgraph screenshot
• Full-duplex loopback: TX attenuation sweep measurements table + brief analysis
• OOK loopback bit accuracy output from Python verification

Grading (10 points)