Lab 11.21 - Capture RTL-SDR monitor WAV during stock-shell ZynqSDR BPSK TX

Objective

Use an RTL-SDR dongle as an independent RF monitor to record the ZynqSDR BPSK transmit burst over the air, while the ZynqSDR operates in stock-shell mode (Lab 11.14 configuration). The resulting WAV file is the primary input to the offline BER analysis in Lab 11.20.

Why an external monitor

The ZynqSDR's own PL RX path is stalled at rx_valid_count = 0 under the runtime overlay. The RTL-SDR provides a completely independent receive chain that is not affected by the course FPGA overlay state, so it can confirm whether the ZynqSDR TX signal is actually radiated — independently of any PL RX issue.

Hardware setup

ZynqSDR TX1 antenna  ─── (air gap, ~1–5 m) ───  RTL-SDR antenna
                                                    │
                                                 USB 2.0
                                                    │
                                                 Host PC
                                               (rtl_sdr / SoapySDR)

• ZynqSDR center frequency: 915 MHz, TX attenuation: -50 dB.
• RTL-SDR tuned to the same center frequency with 10–20 dB tuner gain.
• Antennas must be in the same room; no attenuators needed for this short path.

Files

Path	Purpose
blocks/block_11_integrated_sdr_project/python/lab_11_21_capture_rtl_sdr_monitor_wav.py	start stock-shell BPSK TX, simultaneously capture RTL-SDR WAV, save manifest

Run

python blocks/block_11_integrated_sdr_project/python/\
lab_11_21_capture_rtl_sdr_monitor_wav.py \
  --center-frequency-hz 915000000 \
  --sample-rate-hz 2400000 \
  --tuner-gain-db10 200 \
  --capture-duration-s 5.0 \
  --wav-out datasets/lab11_21_rtl_monitor/capture_live.wav \
  --manifest-out datasets/lab11_21_rtl_monitor/manifest_live.yaml \
  --run-tag stock_bpsk_rtl_monitor

The script:

1. configures the stock AD9361 TX path over SSH (same settings as Lab 11.14);
2. starts a cyclic BPSK burst from the stock host TX DMA;
3. simultaneously opens the RTL-SDR device and records raw I/Q to a WAV file;
4. stops TX after --capture-duration-s seconds;
5. restores the AD9361 to its safe state;
6. saves the WAV file and a YAML manifest with all capture metadata.

WAV output format

codec:       PCM 16-bit signed integer
channels:    2  (left = I, right = Q)
sample rate: --sample-rate-hz value (written into WAV header)
endianness:  little

The WAV can be loaded directly by Lab 11.20 without any conversion.

Key parameters

Parameter	Default	Notes
--center-frequency-hz	915 000 000	Must match ZynqSDR TX LO
--sample-rate-hz	2 400 000	RTL-SDR hardware rate; must be ≥ 2× signal BW
--tuner-gain-db10	200 (= 20.0 dB)	Increase if signal is weak
--capture-duration-s	5.0	Must be long enough to capture full burst

Live result on 2026-06-23

The RTL-SDR captured a 5-second WAV at 2.4 MS/s while the stock-shell BPSK cyclic burst was active. Offline analysis (Lab 11.20) on that WAV found the preamble, recovered 281 bits, and measured BER = 0 / EVM ≈ 55 %. The capture confirms that the ZynqSDR TX1 path radiates a detectable, demodulable BPSK signal at 915 MHz.

Report checklist

• [ ] Confirm RTL-SDR device index and driver (rtlsdr / SoapySDR).
• [ ] Record tuner gain and actual AGC setting.
• [ ] State ZynqSDR TX attenuation and sample rate.
• [ ] Attach the YAML manifest.
• [ ] Cross-reference with Lab 11.20 offline BER result.

Engineering conclusion template

The RTL-SDR monitor captured ____ seconds of WAV at ____ MS/s while the
ZynqSDR stock-shell BPSK TX was active at ____ MHz with TX attenuation ____ dB.
The WAV contains a detectable / undetectable BPSK burst because ____.
Offline Lab 11.20 BER result: ____. OTA TX viability: confirmed / not confirmed.