LoRa receiver flowgraph built entirely through gr-mcp MCP tools.
Successfully decodes live packets from Heltec V3 beacon at 915MHz,
SF7, BW125k via RTL-SDR.
Signal chain: osmosdr(1MSPS) → LPF(200kHz, dec×2) → lora_rx(500kSPS)
→ message_debug
Key settings for RTL-SDR live reception:
- DC offset auto-correction (mode=2) to remove DC spike at center freq
- IQ balance auto-correction (mode=2)
- signal.pause() fallback for Docker detached mode
- XML-RPC on 0.0.0.0 for Docker host accessibility
The container's GNU Radio build doesn't support the log_levels
parameter added in newer GRC versions. Use single-arg form:
blocks.message_debug(True) instead of blocks.message_debug(True, gr.log_levels.info)
Add probe_avg_mag_sqrd_c block that taps the LPF output to measure
filtered RF power. A variable_function_probe polls it and exposes
signal_level via XML-RPC.
Display features:
- Signal strength in dB shown on tune and on 's' command
- Color-coded bar: green (strong), yellow (medium), red (weak)
- Updates after each frequency change
Signal chain now includes measurement tap:
source → LPF → demod → audio
↓
probe → var_function_probe ("signal_level")
Replace template-based prepare_flowgraph() with build_fm_receiver() that
constructs the entire flowgraph in Python code:
- Initialize Platform (same as gr-mcp main.py)
- Create variables: samp_rate, freq
- Create blocks: osmosdr_source, low_pass_filter, analog_wfm_rcv, audio_sink
- Add xmlrpc_server for runtime frequency control
- Connect signal chain: source → LPF → demod → audio
- Save and compile with grcc
This proves gr-mcp's middleware approach works end-to-end: parameters
set via set_params() serialize correctly after the lru_cache fix.
No longer needs examples/fm_receiver.grc template file.
The --tune flag now builds an FM receiver from a GRC template,
compiles it with grcc, launches it as a subprocess, and tunes
via XML-RPC — the same mechanism gr-mcp uses for runtime
parameter changes. Includes an interactive freq> prompt for
live re-tuning without restarting the flowgraph.
--tune flag scans the band then tunes to a station using rtl_fm
piped to aplay. Supports interactive station picker (--tune) or
direct frequency (--tune 102.0).
LLM-driven SDR session recorded 2026-01-28T15:05:21-07:00.
Built flowgraph via MCP tools, launched in Docker with RTL-SDR
USB passthrough, captured 128s of WBFM audio to WAV.
Song identified via songrec/Shazam: "Damn I Love Miami"
by Pitbull & Lil Jon.
Signal chain: RTL2838 → osmocom source (2.4 MS/s)
→ LPF (100 kHz, ÷5) → WBFM demod (÷10) → 48 kHz WAV
Includes GRC flowgraph, WAV recording, and helper scripts.
