     // Check that the radio is correctly connected; panic if not...
     if(!PrimaryRadio.configure(nPrimaryRadioChannels, RFM23BConfigs) || !PrimaryRadio.begin()) { panic(F("r1")); }
 
+  // Turn power on for SIM900 with PFET for secondary power control.
+    fastDigitalWrite(A3, 0);
+    pinMode(A3, OUTPUT);
+  // Initialise the radio, if configured, ASAP because it can suck a lot of power until properly initialised.
+    SecondaryRadio.preinit(NULL);
+//  DEBUG_SERIAL_PRINTLN_FLASHSTRING("R2");
+  // Check that the radio is correctly connected; panic if not...
+    if(!SecondaryRadio.configure(1, &SecondaryRadioConfig) || !SecondaryRadio.begin()) { panic(F("r2")); }
+  // Assume no RX nor filtering on secondary radio.
+
     // Collect full set of environmental values before entering loop() in normal mode.
     // This should also help ensure that sensors are properly initialised.
 

static const OTRadioLink::OTRadioChannelConfig RFM23BConfigs[nPrimaryRadioChannels] = {
    // GFSK channel 0 full config, RX/TX, not in itself secure.
    OTRadioLink::OTRadioChannelConfig(OTRFM23BLink::StandardRegSettingsGFSK57600, true), };

/*
 * TMP112 instance

OTV0P2BASE::SupplyVoltageCentiVolts Supply_cV;

/*
 * RFM23B instance
 */
static constexpr bool RFM23B_allowRX = true;
 
