Ryan Malloy
97248fc069
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.
388 lines
12 KiB
Python
388 lines
12 KiB
Python
#!/usr/bin/env python3
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"""
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FM Receiver Flowgraph Builder using gr-mcp
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This script uses gr-mcp's MCP tools to programmatically build a Wideband FM
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receiver flowgraph that:
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- Receives RF from an RTL-SDR dongle (or simulated source)
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- Demodulates FM audio
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- Outputs to speakers
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Signal Chain:
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RTL-SDR Source (2.4 MHz) → Low Pass Filter → WBFM Demod → Audio Sink
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↓ ↓ ↓ ↓
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88-108 MHz Anti-alias Demodulate Speakers
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complex IQ 200 kHz BW to audio
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"""
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import asyncio
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import sys
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from pathlib import Path
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from fastmcp import Client
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# Add project root to path for imports
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sys.path.insert(0, str(Path(__file__).parent.parent))
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from main import app as mcp_app
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async def find_blocks_matching(client: Client, patterns: list[str]) -> dict[str, str]:
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"""Search available blocks for ones matching the given patterns."""
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result = await client.call_tool(name="get_all_available_blocks")
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available = result.data
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matches = {}
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for pattern in patterns:
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for block in available:
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if pattern.lower() in block.key.lower():
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if pattern not in matches:
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matches[pattern] = block.key
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break
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return matches
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async def build_fm_receiver(
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client: Client,
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freq_mhz: float = 99.5,
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output_path: str = "/tmp/fm_receiver.grc",
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use_simulation: bool = False,
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):
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"""
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Build an FM receiver flowgraph.
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Args:
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client: FastMCP client connected to gr-mcp
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freq_mhz: FM station frequency in MHz (default 99.5)
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output_path: Where to save the .grc file
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use_simulation: If True, use signal source instead of RTL-SDR
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"""
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print(f"\n{'='*60}")
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print(f"Building FM Receiver for {freq_mhz} MHz")
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print(f"{'='*60}\n")
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# Step 1: Find available blocks
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print("Step 1: Checking available blocks...")
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result = await client.call_tool(name="get_all_available_blocks")
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available_blocks = {b.key: b for b in result.data}
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# Check for SDR source options
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sdr_sources = ["osmosdr_source", "soapy_source", "rtlsdr_source"]
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found_sdr = None
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for src in sdr_sources:
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if src in available_blocks:
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found_sdr = src
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print(f" ✓ Found SDR source: {src}")
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break
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if not found_sdr and not use_simulation:
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print(" ⚠ No SDR source found (osmosdr, soapy, rtlsdr)")
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print(" Using simulation mode with analog_sig_source_x")
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use_simulation = True
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# Check for required blocks
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required = ["low_pass_filter", "analog_wfm_rcv", "audio_sink"]
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for block_key in required:
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if block_key in available_blocks:
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print(f" ✓ Found: {block_key}")
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else:
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# Try partial match
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matches = [k for k in available_blocks if block_key in k]
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if matches:
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print(f" ✓ Found (partial): {matches[0]}")
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else:
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print(f" ✗ Missing: {block_key}")
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# Step 2: Create the blocks
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print("\nStep 2: Creating blocks...")
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blocks = {}
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# Source block
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if use_simulation:
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result = await client.call_tool(
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name="make_block", arguments={"block_name": "analog_sig_source_x"}
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)
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blocks["source"] = str(result.data)
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print(f" Created simulation source: {blocks['source']}")
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else:
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result = await client.call_tool(
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name="make_block", arguments={"block_name": found_sdr}
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)
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blocks["source"] = str(result.data)
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print(f" Created SDR source: {blocks['source']}")
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# Low pass filter
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result = await client.call_tool(
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name="make_block", arguments={"block_name": "low_pass_filter"}
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)
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blocks["lpf"] = str(result.data)
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print(f" Created low pass filter: {blocks['lpf']}")
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# WFM (Wideband FM) demodulator
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result = await client.call_tool(
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name="make_block", arguments={"block_name": "analog_wfm_rcv"}
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)
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blocks["wfm"] = str(result.data)
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print(f" Created WFM demod: {blocks['wfm']}")
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# Audio sink
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result = await client.call_tool(
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name="make_block", arguments={"block_name": "audio_sink"}
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)
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blocks["audio"] = str(result.data)
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print(f" Created audio sink: {blocks['audio']}")
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# Step 3: Configure block parameters
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print("\nStep 3: Configuring block parameters...")
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freq_hz = freq_mhz * 1e6
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samp_rate = 2.4e6 # 2.4 MHz sample rate
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audio_rate = 48000 # 48 kHz audio
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if use_simulation:
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# Configure simulation source (complex sine wave at FM frequency)
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# Using GRC parameter keys (not display names) from inspect_blocks.py
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await client.call_tool(
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name="set_block_params",
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arguments={
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"block_name": blocks["source"],
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"params": {
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"type": "complex",
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"samp_rate": str(samp_rate),
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"freq": "1000", # 1 kHz tone offset
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"amp": "1",
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"offset": "0",
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"waveform": "analog.GR_COS_WAVE",
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},
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},
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)
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print(f" Configured simulation source (complex, {samp_rate/1e6} MHz)")
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else:
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# Configure RTL-SDR/OsmoSDR source
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# Using GRC parameter keys (not display names) from inspect_blocks.py
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await client.call_tool(
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name="set_block_params",
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arguments={
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"block_name": blocks["source"],
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"params": {
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"type": "fc32",
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"args": '"rtl=0"',
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"sample_rate": str(samp_rate),
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"freq0": str(freq_hz),
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"gain0": "40",
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"if_gain0": "20",
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"bb_gain0": "20",
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},
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},
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)
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print(f" Configured SDR source: {freq_mhz} MHz, {samp_rate/1e6} MS/s")
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# Configure low pass filter
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# Decimation: 2.4M → 480k (factor of 5)
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# Using GRC parameter keys (not display names) from inspect_blocks.py
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await client.call_tool(
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name="set_block_params",
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arguments={
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"block_name": blocks["lpf"],
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"params": {
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"type": "fir_filter_ccf",
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"decim": "5",
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"gain": "1",
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"samp_rate": str(samp_rate),
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"cutoff_freq": "100e3", # 100 kHz cutoff
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"width": "10e3", # 10 kHz transition width
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"win": "window.WIN_HAMMING",
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},
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},
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)
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print(" Configured LPF: 100 kHz cutoff, 5x decimation → 480 kHz")
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# Configure WFM demodulator
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# Input rate: 480 kHz, audio decimation: 10 → 48 kHz audio
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# Using GRC parameter keys (not display names) from inspect_blocks.py
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await client.call_tool(
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name="set_block_params",
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arguments={
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"block_name": blocks["wfm"],
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"params": {
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"quad_rate": "480e3", # 480 kHz input rate
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"audio_decimation": "10", # → 48 kHz output
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},
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},
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)
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print(" Configured WFM: quad_rate=480k, audio_dec=10 → 48 kHz")
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# Configure audio sink
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# Using GRC parameter keys (not display names) from inspect_blocks.py
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await client.call_tool(
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name="set_block_params",
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arguments={
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"block_name": blocks["audio"],
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"params": {
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"samp_rate": str(audio_rate),
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"device_name": "", # Default audio device
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"ok_to_block": "True",
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"num_inputs": "1",
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},
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},
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)
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print(f" Configured audio sink: {audio_rate} Hz")
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# Step 4: Check block ports before connecting
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print("\nStep 4: Checking block ports...")
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for name, block_name in blocks.items():
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sources = await client.call_tool(
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name="get_block_sources", arguments={"block_name": block_name}
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)
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sinks = await client.call_tool(
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name="get_block_sinks", arguments={"block_name": block_name}
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)
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src_count = len(sources.data) if sources.data else 0
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sink_count = len(sinks.data) if sinks.data else 0
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print(f" {name} ({block_name}): {src_count} source(s), {sink_count} sink(s)")
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# Step 5: Connect the signal chain
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print("\nStep 5: Connecting signal chain...")
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# Source → Low Pass Filter
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await client.call_tool(
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name="connect_blocks",
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arguments={
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"source_block_name": blocks["source"],
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"sink_block_name": blocks["lpf"],
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"source_port_name": "0",
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"sink_port_name": "0",
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},
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)
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print(f" {blocks['source']}:0 → {blocks['lpf']}:0")
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# Low Pass Filter → WBFM Demod
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await client.call_tool(
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name="connect_blocks",
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arguments={
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"source_block_name": blocks["lpf"],
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"sink_block_name": blocks["wfm"],
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"source_port_name": "0",
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"sink_port_name": "0",
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},
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)
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print(f" {blocks['lpf']}:0 → {blocks['wfm']}:0")
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# WBFM Demod → Audio Sink
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await client.call_tool(
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name="connect_blocks",
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arguments={
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"source_block_name": blocks["wfm"],
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"sink_block_name": blocks["audio"],
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"source_port_name": "0",
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"sink_port_name": "0",
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},
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)
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print(f" {blocks['wfm']}:0 → {blocks['audio']}:0")
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# Step 6: Validate the flowgraph
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print("\nStep 6: Validating flowgraph...")
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valid = await client.call_tool(name="validate_flowgraph")
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if valid.data:
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print(" ✓ Flowgraph is valid")
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else:
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print(" ✗ Flowgraph has errors:")
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errors = await client.call_tool(name="get_all_errors")
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for err in errors.data:
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print(f" - {err}")
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# Step 7: Get all connections for verification
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print("\nStep 7: Verifying connections...")
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conns = await client.call_tool(name="get_connections")
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for conn in conns.data:
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# ConnectionModel has source/sink PortModels with parent (block) and key (port)
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print(
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f" {conn.source.parent}:{conn.source.key} → "
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f"{conn.sink.parent}:{conn.sink.key}"
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)
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# Step 8: Save the flowgraph
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print(f"\nStep 8: Saving flowgraph to {output_path}...")
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await client.call_tool(
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name="save_flowgraph", arguments={"filepath": output_path}
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)
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print(f" ✓ Saved to {output_path}")
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# Summary
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print(f"\n{'='*60}")
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print("FM Receiver Flowgraph Complete!")
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print(f"{'='*60}")
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print(f" Frequency: {freq_mhz} MHz")
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print(f" Sample Rate: {samp_rate/1e6} MS/s")
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print(f" Audio Rate: {audio_rate} Hz")
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print(f" Output: {output_path}")
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if use_simulation:
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print(" Mode: SIMULATION (no RTL-SDR)")
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else:
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print(" Mode: RTL-SDR")
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print()
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return blocks
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async def list_all_blocks(client: Client, filter_pattern: str = None):
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"""List all available GNU Radio blocks, optionally filtered."""
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result = await client.call_tool(name="get_all_available_blocks")
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blocks = sorted(result.data, key=lambda b: b.key)
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if filter_pattern:
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blocks = [b for b in blocks if filter_pattern.lower() in b.key.lower()]
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print(f"\nAvailable blocks ({len(blocks)} total):")
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for block in blocks:
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print(f" {block.key}")
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return blocks
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async def main():
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"""Main entry point."""
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import argparse
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parser = argparse.ArgumentParser(description="Build FM Receiver with gr-mcp")
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parser.add_argument(
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"--freq", type=float, default=99.5, help="FM frequency in MHz (default: 99.5)"
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)
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parser.add_argument(
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"--output",
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type=str,
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default="/tmp/fm_receiver.grc",
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help="Output .grc file path",
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)
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parser.add_argument(
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"--simulate",
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action="store_true",
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help="Use simulated source instead of RTL-SDR",
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)
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parser.add_argument(
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"--list-blocks",
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type=str,
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nargs="?",
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const="",
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help="List available blocks (optionally filter by pattern)",
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)
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args = parser.parse_args()
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async with Client(mcp_app) as client:
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if args.list_blocks is not None:
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await list_all_blocks(
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client, args.list_blocks if args.list_blocks else None
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)
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else:
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await build_fm_receiver(
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client,
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freq_mhz=args.freq,
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output_path=args.output,
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use_simulation=args.simulate,
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)
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if __name__ == "__main__":
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asyncio.run(main())
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