The radio's noise: the GNSS receiver costs 8 dB; a setting pauses it (#20)

Debug Builds: `lora noise test` changes one thing at a time, Sweeps the
band, and reports the floor under each condition; it runs on the device
by itself, since one condition pauses Wi-Fi (not saved, so a restart
brings it back). Result, at 125 kHz: -117 dBm with the antenna switched
off, -106 with the GNSS receiver in standby, -98 with it running. The
receiver's serial line isn't it (one sentence a second changes nothing),
and neither are the main loop, the CPU frequency, Wi-Fi, the screen or
the radio's own regulator, all within 1 dB.

Settings > "Pause GNSS for LoRa", off by default: the receiver waits in
standby while the radio listens or sweeps, except during a Track, and
has a Fix again about 7 s after. The GNSS App says it's paused.

11 dB remain between the antenna with GNSS quiet and the chip alone,
untouched by anything that can be switched from the firmware.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/services/radio_service.cpp

@@ -71,19 +71,19 @@ bool RadioService::beginRadio(Print* report) {
     Config c = config();
     float mhz = c.frequencyHz / 1e6f;
     int16_t state = radio_->begin(mhz, c.bandwidthKHz, c.spreadingFactor, c.codingRate, c.syncWord, 0, c.preamble,
-                                  tcxo_, false);
+                                  tcxo_, ldo_);
     if (state != RADIOLIB_ERR_NONE && tcxo_ > 0) {  // Meshtastic's TCXO_OPTIONAL: fall back to the crystal
         if (report) report->printf("lora probe: begin with TCXO %.1f V: error %d, trying the crystal\n", tcxo_, state);
         tcxo_ = 0;
         state = radio_->begin(mhz, c.bandwidthKHz, c.spreadingFactor, c.codingRate, c.syncWord, 0, c.preamble, tcxo_,
-                              false);
+                              ldo_);
     }
     if (state != RADIOLIB_ERR_NONE) {
         if (report) report->printf("lora probe: error %d, no SX1262 found\n", state);
         return false;
     }
     radio_->setDio2AsRfSwitch(true);       // DIO2 selects TX or RX in the switch, as in Meshtastic
-    radio_->setRxBoostedGainMode(true);    // about 2 dB more sensitivity for about 2 mA
+    radio_->setRxBoostedGainMode(boostedGain_);  // about 2 dB more sensitivity for about 2 mA
     return true;
 }
 
@@ -191,6 +191,12 @@ void RadioService::store(RadioPacket& p) {
 }
 
 #ifdef RORO_DEBUG
+void RadioService::debugAntenna(bool on) {
+    auto& i2c = M5.In_I2C;
+    uint8_t out = i2c.readRegister8(kExpander, kOutput, kI2cFreq);
+    i2c.writeRegister8(kExpander, kOutput, on ? (out | 1) : (out & ~1), kI2cFreq);
+}
+
 void RadioService::inject(const uint8_t* data, size_t len, float rssi, float snr) {
     if (!listening_) return (void)console.println("lora inject: not listening");
     RadioPacket p;