Add SDRPlay device support via SoapySDR

Adds support for SDRPlay RSP devices (RSPdx, RSP1A, RSPduo, etc.)
through the SoapySDR interface. Closes #44.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

utils/sdr/sdrplay.py

@@ -0,0 +1,143 @@
+"""
+SDRPlay command builder implementation.
+
+Uses SoapySDR-based tools for FM demodulation and signal capture.
+SDRPlay RSP devices support 1 kHz to 2 GHz frequency range.
+"""
+
+from __future__ import annotations
+
+from typing import Optional
+
+from .base import CommandBuilder, SDRCapabilities, SDRDevice, SDRType
+
+
+class SDRPlayCommandBuilder(CommandBuilder):
+    """SDRPlay command builder using SoapySDR tools."""
+
+    # SDRPlay RSP capabilities (RSPdx, RSP1A, RSPduo, etc.)
+    CAPABILITIES = SDRCapabilities(
+        sdr_type=SDRType.SDRPLAY,
+        freq_min_mhz=0.001,      # 1 kHz
+        freq_max_mhz=2000.0,     # 2 GHz
+        gain_min=0.0,
+        gain_max=59.0,           # IFGR range
+        sample_rates=[62500, 96000, 125000, 192000, 250000, 384000, 500000, 1000000, 2000000],
+        supports_bias_t=True,
+        supports_ppm=False,      # SDRPlay has TCXO, no PPM needed
+        tx_capable=False
+    )
+
+    def _build_device_string(self, device: SDRDevice) -> str:
+        """Build SoapySDR device string for SDRPlay."""
+        if device.serial and device.serial != 'N/A':
+            return f'driver=sdrplay,serial={device.serial}'
+        return 'driver=sdrplay'
+
+    def build_fm_demod_command(
+        self,
+        device: SDRDevice,
+        frequency_mhz: float,
+        sample_rate: int = 22050,
+        gain: Optional[float] = None,
+        ppm: Optional[int] = None,
+        modulation: str = "fm",
+        squelch: Optional[int] = None,
+        bias_t: bool = False
+    ) -> list[str]:
+        """
+        Build SoapySDR rx_fm command for FM demodulation.
+
+        For pager decoding with SDRPlay.
+        """
+        device_str = self._build_device_string(device)
+
+        cmd = [
+            'rx_fm',
+            '-d', device_str,
+            '-f', f'{frequency_mhz}M',
+            '-M', modulation,
+            '-s', str(sample_rate),
+        ]
+
+        if gain is not None and gain > 0:
+            cmd.extend(['-g', f'IFGR={int(gain)}'])
+
+        if squelch is not None and squelch > 0:
+            cmd.extend(['-l', str(squelch)])
+
+        if bias_t:
+            cmd.extend(['-T'])
+
+        # Output to stdout
+        cmd.append('-')
+
+        return cmd
+
+    def build_adsb_command(
+        self,
+        device: SDRDevice,
+        gain: Optional[float] = None,
+        bias_t: bool = False
+    ) -> list[str]:
+        """
+        Build dump1090/readsb command with SoapySDR support for ADS-B decoding.
+
+        Uses readsb which has better SoapySDR support.
+        """
+        device_str = self._build_device_string(device)
+
+        cmd = [
+            'readsb',
+            '--net',
+            '--device-type', 'soapysdr',
+            '--device', device_str,
+            '--quiet'
+        ]
+
+        if gain is not None:
+            cmd.extend(['--gain', str(int(gain))])
+
+        if bias_t:
+            cmd.extend(['--enable-bias-t'])
+
+        return cmd
+
+    def build_ism_command(
+        self,
+        device: SDRDevice,
+        frequency_mhz: float = 433.92,
+        gain: Optional[float] = None,
+        ppm: Optional[int] = None,
+        bias_t: bool = False
+    ) -> list[str]:
+        """
+        Build rtl_433 command with SoapySDR support for ISM band decoding.
+
+        rtl_433 has native SoapySDR support via -d flag.
+        """
+        device_str = self._build_device_string(device)
+
+        cmd = [
+            'rtl_433',
+            '-d', device_str,
+            '-f', f'{frequency_mhz}M',
+            '-F', 'json'
+        ]
+
+        if gain is not None and gain > 0:
+            cmd.extend(['-g', str(int(gain))])
+
+        if bias_t:
+            cmd.extend(['-T'])
+
+        return cmd
+
+    def get_capabilities(self) -> SDRCapabilities:
+        """Return SDRPlay capabilities."""
+        return self.CAPABILITIES
+
+    @classmethod
+    def get_sdr_type(cls) -> SDRType:
+        """Return SDR type."""
+        return SDRType.SDRPLAY