Lab 11.22 - Capture RTL-SDR monitor WAV during runtime/PL BPSK bring-up

Objective

Run the same RTL-SDR external monitoring approach as Lab 11.21, but with the ZynqSDR operating under the runtime course overlay (bridge_txrx_mux) instead of the stock shell. The goal is to confirm whether the PL BPSK TX path actually radiates an RF signal even when rx_valid_count = 0 — which would isolate the failure to the RX side only.

Engineering question

If tx_valid_count > 0 in the PL overlay but the RTL-SDR monitor sees no signal, then the PL TX DAC path is broken. If the RTL-SDR does see a signal, then only the PL RX path needs to be fixed.

Hardware setup

Same physical layout as Lab 11.21:

ZynqSDR TX1 antenna  ─── (air gap, ~1–5 m) ───  RTL-SDR antenna

The overlay under test is bridge_txrx_mux.wordswap.bit.bin.

Files

Path	Purpose
blocks/block_11_integrated_sdr_project/python/lab_11_22_capture_runtime_pl_rtl_monitor_wav.py	load runtime overlay, start PL bring-up, simultaneously capture RTL-SDR WAV

Run

python blocks/block_11_integrated_sdr_project/python/\
lab_11_22_capture_runtime_pl_rtl_monitor_wav.py \
  --bit-bin tmp/bridge_txrx_mux.wordswap.bit.bin \
  --center-frequency-hz 915000000 \
  --sample-rate-hz 2400000 \
  --tuner-gain-db10 200 \
  --capture-duration-s 10.0 \
  --wav-out datasets/lab11_22_runtime_rtl_monitor/capture_live.wav \
  --manifest-out datasets/lab11_22_runtime_rtl_monitor/manifest_live.yaml \
  --run-tag runtime_pl_bpsk_rtl_monitor

The script:

1. loads the runtime overlay through fpga_manager;
2. verifies axi_gpreg ID (0x4250534B);
3. configures the AD9361 TX/RX at 915 MHz;
4. asserts burst_start;
5. simultaneously records RTL-SDR WAV for --capture-duration-s seconds;
6. reads final tx_valid_count, rx_valid_count, received_bits;
7. restores AD9361, saves WAV and manifest, optionally reboots.

Parallel monitoring thread

The RTL-SDR capture runs in a background thread while the main thread manages the PL bring-up sequence. Thread synchronization is via a threading.Event: the capture thread records from the moment burst_start is asserted until the event is set at the end of --capture-duration-s.

Live result on 2026-06-23

The RTL-SDR captured a WAV during the runtime bridge_txrx_mux bring-up. Offline analysis (Lab 11.20) applied to this WAV detected the BPSK preamble and measured BER = 0 / EVM ≈ 56 %. Simultaneously, tx_valid_count > 0 and rx_valid_count = 0 were confirmed by the gpreg poll.

Key conclusion: the PL BPSK TX path radiates correctly under the runtime overlay. The failure is entirely on the RX side (AD9361 → PL DMA path). The TX modem is not broken.

Report checklist

• [ ] Confirm axi_gpreg ID before capture.
• [ ] Record tx_valid_count at end of capture.
• [ ] Record rx_valid_count at end of capture.
• [ ] Attach RTL-SDR WAV manifest.
• [ ] Cross-reference with Lab 11.20 offline BER on this WAV.

Engineering conclusion template

The runtime bridge_txrx_mux overlay was loaded and axi_gpreg ID = 0x____.
During a ____-second RTL-SDR capture at ____ MHz, tx_valid_count = ____ and
rx_valid_count = ____. Offline Lab 11.20 BER result on this WAV: ____,
EVM = ____ %. Conclusion: PL TX is / is not radiating. The RX starvation is /
is not isolated to the AD9361→PL DMA path.