From 3f9cd2e4e0a3b2fd3bcf5fbdbab65bdb842c98ad Mon Sep 17 00:00:00 2001
From: Ben Meadors <benmmeadors@gmail.com>
Date: Sun, 14 Jun 2026 18:47:20 -0500
Subject: [PATCH] Update US LoRa modem preset to region defaults for compliance

---
 src/mesh/Channels.cpp               |  2 +-
 src/mesh/NodeDB.cpp                 |  5 ++++-
 src/mesh/RadioInterface.cpp         |  7 ++++++-
 test/test_admin_radio/test_main.cpp | 24 ++++++++++++++++++++++++
 4 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/src/mesh/Channels.cpp b/src/mesh/Channels.cpp
index be75e3d42..90bca6c40 100644
--- a/src/mesh/Channels.cpp
+++ b/src/mesh/Channels.cpp
@@ -82,7 +82,7 @@ void Channels::initDefaultLoraConfig()
 {
     meshtastic_Config_LoRaConfig &loraConfig = config.lora;
 
-    loraConfig.modem_preset = meshtastic_Config_LoRaConfig_ModemPreset_LONG_FAST; // Default to Long Range & Fast
+    loraConfig.modem_preset = getRegion(loraConfig.region)->getDefaultPreset(); // region default (US: LONG_TURBO for FCC)
     loraConfig.use_preset = true;
     loraConfig.tx_power = 0; // default
     loraConfig.channel_num = 0;
diff --git a/src/mesh/NodeDB.cpp b/src/mesh/NodeDB.cpp
index 2481eb8ca..ea22ae175 100644
--- a/src/mesh/NodeDB.cpp
+++ b/src/mesh/NodeDB.cpp
@@ -834,7 +834,10 @@ void NodeDB::installDefaultConfig(bool preserveKey = false)
 #ifdef USERPREFS_LORACONFIG_MODEM_PRESET
     config.lora.modem_preset = USERPREFS_LORACONFIG_MODEM_PRESET;
 #else
-    config.lora.modem_preset = meshtastic_Config_LoRaConfig_ModemPreset_LONG_FAST;
+    // Default to the region's own default preset (US is LONG_TURBO for FCC §15.247; every other region
+    // is LONG_FAST). region is set just above, so a region-locked board is born on the compliant default
+    // without any runtime "upgrade" step.
+    config.lora.modem_preset = getRegion(config.lora.region)->getDefaultPreset();
 #endif
 #ifdef USERPREFS_LORACONFIG_USE_PRESET
     config.lora.use_preset = USERPREFS_LORACONFIG_USE_PRESET;
diff --git a/src/mesh/RadioInterface.cpp b/src/mesh/RadioInterface.cpp
index 0d973e2e2..858803cd2 100644
--- a/src/mesh/RadioInterface.cpp
+++ b/src/mesh/RadioInterface.cpp
@@ -77,7 +77,12 @@ const RegionInfo regions[] = {
         https://link.springer.com/content/pdf/bbm%3A978-1-4842-4357-2%2F1.pdf
         https://www.thethingsnetwork.org/docs/lorawan/regional-parameters/
     */
-    RDEF(US, 902.0f, 928.0f, 100, 30, false, false, PROFILE_STD, PRESET(LONG_FAST), 0),
+    // FCC §15.247 requires >=500 kHz of 6 dB bandwidth for digital (non-frequency-hopping)
+    // modulation in the 902-928 MHz band, so the US region's default preset is LONG_TURBO (500 kHz)
+    // rather than the 250 kHz LONG_FAST. A fresh US board adopts this as its factory default via
+    // getDefaultPreset() (see installDefaultConfig); LONG_FAST and the other presets stay available
+    // for users who opt in.
+    RDEF(US, 902.0f, 928.0f, 100, 30, false, false, PROFILE_STD, PRESET(LONG_TURBO), 0),
 
     /*
         EN300220 ETSI V3.2.1 [Table B.1, Item H, p. 21]
diff --git a/test/test_admin_radio/test_main.cpp b/test/test_admin_radio/test_main.cpp
index d905cc8a0..b110e7ebb 100644
--- a/test/test_admin_radio/test_main.cpp
+++ b/test/test_admin_radio/test_main.cpp
@@ -1112,6 +1112,26 @@ void tearDown(void)
     testAdmin = nullptr;
 }
 
+// -----------------------------------------------------------------------
+// US region factory default preset (LONG_TURBO for FCC §15.247). A fresh board adopts its region's
+// default via getDefaultPreset() in installDefaultConfig() — there is no runtime "upgrade" path.
+// -----------------------------------------------------------------------
+
+static void test_usRegionDefaultPresetIsLongTurbo()
+{
+    // FCC §15.247: the US region's default preset is the 500 kHz LONG_TURBO, so a fresh US board is
+    // born compliant.
+    TEST_ASSERT_EQUAL(meshtastic_Config_LoRaConfig_ModemPreset_LONG_TURBO,
+                      getRegion(meshtastic_Config_LoRaConfig_RegionCode_US)->getDefaultPreset());
+}
+
+static void test_nonUsRegionDefaultPresetUnchanged()
+{
+    // Only US changed: every other region still defaults to LONG_FAST.
+    TEST_ASSERT_EQUAL(meshtastic_Config_LoRaConfig_ModemPreset_LONG_FAST,
+                      getRegion(meshtastic_Config_LoRaConfig_RegionCode_EU_868)->getDefaultPreset());
+}
+
 void setup()
 {
     delay(10);
@@ -1180,6 +1200,10 @@ void setup()
     RUN_TEST(test_regionFieldsAreSane);
     RUN_TEST(test_onlyLORA24HasWideLora);
 
+    // US region factory default preset
+    RUN_TEST(test_usRegionDefaultPresetIsLongTurbo);
+    RUN_TEST(test_nonUsRegionDefaultPresetUnchanged);
+
     // OVERRIDE_SLOT_PRESET_HASH (-1) slot formula tests
     RUN_TEST(test_overrideSlotPresetHash_longFast_customChannelMatchesDefaultNameSlot);
     RUN_TEST(test_overrideSlotPresetHash_mediumFast_customChannelMatchesDefaultNameSlot);