implement radio.fem.rxgain

releasenotes/RELEASE_NOTES_1.17.2-zephcore.md

@@ -191,6 +191,31 @@ An LR1110 running firmware older than 0x0303 cannot be moved off the public LoRa
 and receives perfectly well, but nobody on your mesh can see it. That now appears in the log instead of
 looking like a broken radio.
 
+## New setting: switch the antenna amplifier's receive gain off
+
+Some boards carry an extra amplifier chip between the radio and the antenna. It boosts what the node
+transmits, and on the way in it boosts what the node hears. It has always been switched on for both, and
+it stays that way — **nothing changes unless you change it.**
+
+The new `set radio.fem.rxgain 0` switches off only the receive side, to save the current that part of the
+amplifier draws. Transmitting is untouched: every packet the node sends still goes out through the
+amplifier at full strength. `set radio.fem.rxgain 1` puts it back, and `get radio.fem.rxgain` shows where
+it stands. The node keeps the setting across reboots.
+
+> [!WARNING]
+> **This costs range, and a lot of it.** With the receive side off the node goes substantially deafer —
+> on a Wireless Tracker V2 the measured noise floor moves by about 23 dB between the two settings. Distant
+> and weak neighbours simply stop being heard, while the node's own transmissions carry exactly as far as
+> before, so from the outside it still looks perfectly healthy. Only worth doing on a battery-powered node
+> where you already know every neighbour is close and strong.
+
+Supported on the **Heltec T096**, **Wireless Tracker V2**, **WiFi LoRa 32 V4** and **WiFi LoRa 32 V4.3**.
+Everything else replies `Error: unsupported` — either the board has no such amplifier, or its amplifier is
+switched on by a line the radio driver cannot reach. The **RAK3401 1 W** is in that second group.
+
+Proposed by **bisbille** ([@bisbille](https://github.com/bisbille)) —
+[#74](https://github.com/liquidraver/ZephCore/pull/74).
+
 ---
 
 ## Also in this release
@@ -219,3 +244,7 @@ Housekeeping, listed for completeness — nothing here changes how a node behave
   but no real node has been broken and recovered. Normal healthy nodes are unaffected.
 - **Why that one node's identity broke is still unknown.** This release makes sure the same thing can no
   longer go unnoticed, but the original cause has not been found.
+- **The antenna amplifier receive setting is compile-checked on every affected board, but has not been
+  measured on hardware in this form.** The 23 dB figure above comes from the original proposal, which
+  reached the same pin by a different route. Leaving the setting alone keeps every node behaving exactly
+  as it did before, so a node nobody deliberately switches over is not affected at all.

zephcore/Repeater_CLI_commands.md

@@ -260,6 +260,7 @@ All `set uplink.*` changes are saved immediately and only applied after reboot.
 | `get path.hash.mode` | Path hashing algorithm: `0`, `1`, or `2` |
 | `get loop.detect` | Loop detection level: `off`, `minimal`, `moderate`, or `strict` |
 | `get radio.rxgain` | RX gain boost: `0` or `1` |
+| `get radio.fem.rxgain` | External FEM/LNA active during RX: `0` or `1` (default `1`) |
 | `get rxduty` | RX duty cycle mode: `0` or `1` |
 | `get gps duty` | Now-effective GPS duty interval in seconds (`always on (0)` when continuous) |
 | `get gps diag` | What the last GPS module-configuration attempt did — which path ran, bytes sent, and tracked satellites per constellation. See **GPS configuration diagnostics** in the GPS section for the field reference |
@@ -310,6 +311,7 @@ Changes are persisted immediately unless noted. Some require a reboot.
 | `set path.hash.mode <mode>` | 0, 1, or 2 | Path hashing algorithm |
 | `set loop.detect <mode>` | `off`, `minimal`, `moderate`, `strict` | Loop detection sensitivity |
 | `set radio.rxgain <0\|1\|on\|off>` | | RX gain boost, applied live. Replies `Error: unsupported` on radios without RX boost (SX127x); the pref is still saved. |
+| `set radio.fem.rxgain <0\|1\|on\|off>` | default **1** | External FEM/LNA gating in the RX direction, applied live. Supported only where the FEM's chip-enable is wired to the radio node as `antenna-enable-gpios` — today `heltec_t096`, `heltec_wireless_tracker_v2`, `heltec_wifi_lora32_v4` and `heltec_wifi_lora32_v43`. Every other board reports `Error: unsupported`, for one of three reasons: it has no external amplifier at all; its amplifier has no separate receive-side enable, only the DIO2/TXEN/RXEN transmit-receive switch (`station_g2`, `gat562_30s`, `ikoka_nano_30dbm`, `promicro_sx1262`); or its amplifier enable is a standalone always-on regulator outside the radio node (`rak3401_1watt` — moving that pin onto the lora node as `antenna-enable-gpios` is what would enable it). Non-SX126x radios (LR1110, LR2021, SX127x) never support it. Setting `0` drops the FEM's RX gain (~16 dB on the SKY66122) and its supply current (~6.5 mA) — sensitivity for battery life, not a tuning knob. Transmit always uses the FEM, and the driver's idle/sleep gating is unchanged. Replies `Error: unsupported` on non-SX126x radios and on boards with no FEM wired; the pref is still saved. |
 | `set rxduty <0\|1\|on\|off>` | | RX duty cycle mode *(reboot required)*. Window timing auto-sized per SF/BW/preamble from the SX126x datasheet constraints (boot log line `rxduty:` shows the result). Zero-loss guarantee assumes senders on preamble-32 firmware (current MeshCore at SF≤8); legacy preamble-16 senders are only caught ~50% worst-phase — keep off until the local mesh has converted. Presets with 16-symbol preambles (SF≥9) fall back to continuous RX automatically. |
 | `set adc.multiplier <mult>` | `0` (use board default) or 100–30000 | Battery voltage ADC calibration multiplier, set directly. Rejects non-numeric input, NaN/inf and negatives. |
 | `set adc.multiplier target <mv>` | 3000–4400 mV | Calibrate against a voltage you measured with a multimeter: rescales the current multiplier so the ADC reads `<mv>`. Replies with the old and new multiplier plus the before/after reading. `Error: no ADC reading on this board` if the board has no battery ADC. |

zephcore/adapters/datastore/ZephyrDataStore.cpp

@@ -866,6 +866,14 @@ void ZephyrDataStore::loadPrefs(NodePrefs &prefs)
 		prefs.v_contact_flags = buf[off++];
 	}
 
+	/* Offset 167: fem_rxgain (ZephCore extension).  Absent in pre-existing
+	 * files → keeps the caller's initNodePrefs() default of 1, which is the
+	 * behaviour every deployed node already has (the FEM's chip-enable has
+	 * always been asserted for RX). */
+	if (off < len) {
+		prefs.fem_rxgain = buf[off++];
+	}
+
 	sanitizeNodePrefs(&prefs);
 }
 
@@ -966,7 +974,9 @@ void ZephyrDataStore::savePrefs(const NodePrefs &prefs)
 	off += EXTRA_SF_MAX;
 	/* Offset 166: v_contact_flags (ZephCore extension) */
 	buf[off++] = prefs.v_contact_flags;
-	/* Total: 167 bytes */
+	/* Offset 167: fem_rxgain (ZephCore extension, external FEM LNA in RX) */
+	buf[off++] = prefs.fem_rxgain;
+	/* Total: 168 bytes */
 
 	bool ok = atomicReplaceFile(PREFS_FILE, buf, off);
 	LOG_DBG("savePrefs: wrote %s, ok=%d (%d bytes), name='%.16s'",

zephcore/adapters/radio/LoRaRadioBase.h

@@ -85,6 +85,16 @@ public:
 	virtual bool setRxBoost(bool enable);
 	bool isRxBoostEnabled() const { return _rx_boost_enabled; }
 
+	/* External FEM/LNA gain during RX.  Boards carrying a front-end module
+	 * wire its chip-enable to the radio's antenna-enable line, which the
+	 * driver asserts for RX and TX alike; disabling this withholds it in the
+	 * RX direction only, trading the FEM's RX gain for its supply current.
+	 * The transmit path and the driver's idle gating are unaffected.
+	 * Returns false on radios that do not implement the knob (everything but
+	 * the native SX126x today); on an SX126x board with no FEM wired it
+	 * succeeds and does nothing, since there is no pin to withhold. */
+	virtual bool setFemRxEnable(bool enable) { (void)enable; return false; }
+
 	/* Multi-SF receive via LoRa side detectors.  Only the LR2021 has them;
 	 * every other radio reports the feature as unsupported.  `num` = 0
 	 * disables.  Returns false if the radio has no side detectors or the

zephcore/adapters/radio/SX126xRadio.cpp

@@ -101,6 +101,20 @@ void SX126xRadio::hwSetRxBoost(bool enable)
 	sx126x_set_rx_boost(_dev, enable);
 }
 
+bool SX126xRadio::setFemRxEnable(bool enable)
+{
+	/* Pure driver-side flag -- no SPI, no chip state.  It takes effect at the
+	 * next RX/TX/sleep transition, and startReceive() goes through one, so
+	 * there is nothing to re-apply here.  Returns false when this board wires
+	 * no antenna-enable line, so the CLI reports "unsupported" rather than
+	 * acknowledging a setting that cannot do anything. */
+	if (!sx126x_set_fem_rx_enable(_dev, enable)) {
+		return false;
+	}
+	LOG_INF("FEM RX gain %s", enable ? "enabled" : "disabled");
+	return true;
+}
+
 bool SX126xRadio::hwIsChipBusy()
 {
 	return sx126x_is_chip_busy(_dev);

zephcore/adapters/radio/SX126xRadio.h

@@ -16,6 +16,11 @@ public:
 
 	void begin() override;
 
+	/* Gate the external FEM's LNA in the RX direction (radio.fem.rxgain).
+	 * Delegates to the driver, which owns the antenna-enable pin; returns
+	 * false on a board that has no such pin, i.e. no FEM to gate. */
+	bool setFemRxEnable(bool enable) override;
+
 	/* Duty-cycle preamble false-positive stats (SX126x-specific) */
 	uint32_t getDutyCycleTimeoutRestarts() const override;
 	void resetDutyCycleTimeoutRestarts() override;

zephcore/app/RepeaterDataStore.cpp

@@ -236,6 +236,10 @@ bool RepeaterDataStore::loadPrefs(NodePrefs& prefs) {
     /* LR2021 side-detector SFs, offsets 301-303.  Absent in <304-byte files;
      * the no-op EOF read leaves the zeroed default = feature off. */
     fs_read(&file, prefs.extra_sf, sizeof(prefs.extra_sf));
+    /* External FEM RX gain, offset 304.  Absent in <305-byte files; the no-op
+     * EOF read keeps the initNodePrefs() default fem_rxgain=1, which is what
+     * every already-deployed node has been running. */
+    fs_read(&file, &prefs.fem_rxgain, sizeof(prefs.fem_rxgain));
 
     fs_close(&file);
 
@@ -379,6 +383,8 @@ bool RepeaterDataStore::savePrefs(const NodePrefs& prefs) {
     fs_write(&file, &prefs.cad_busycap, sizeof(prefs.cad_busycap));
     /* LR2021 side-detector SFs (offsets 301-303) */
     fs_write(&file, prefs.extra_sf, sizeof(prefs.extra_sf));
+    /* External FEM RX gain (offset 304) */
+    fs_write(&file, &prefs.fem_rxgain, sizeof(prefs.fem_rxgain));
 
     ret = fs_sync(&file);
     fs_close(&file);

zephcore/app/RepeaterMesh.cpp

@@ -1253,6 +1253,10 @@ bool RepeaterMesh::setRxBoostedGain(bool enable) {
     return getRadioDriver(_radio).setRxBoost(enable);
 }
 
+bool RepeaterMesh::setFemRxGain(bool enable) {
+    return getRadioDriver(_radio).setFemRxEnable(enable);
+}
+
 bool RepeaterMesh::configSideDetectors(const uint8_t* sfs, uint8_t num) {
     return getRadioDriver(_radio).configSideDetectors(sfs, num);
 }

zephcore/app/RepeaterMesh.h

@@ -258,6 +258,7 @@ public:
     void dumpLogFile() override;
     void setTxPower(int8_t power_dbm) override;
     bool setRxBoostedGain(bool enable) override;
+    bool setFemRxGain(bool enable) override;
     bool configSideDetectors(const uint8_t* sfs, uint8_t num) override;
     void formatNeighborsReply(char* reply) override;
     void removeNeighbor(const uint8_t* pubkey, int key_len) override;

zephcore/app/RoomServerMesh.cpp

@@ -957,6 +957,10 @@ bool RoomServerMesh::setRxBoostedGain(bool enable) {
     return getRadioDriver(_radio).setRxBoost(enable);
 }
 
+bool RoomServerMesh::setFemRxGain(bool enable) {
+    return getRadioDriver(_radio).setFemRxEnable(enable);
+}
+
 bool RoomServerMesh::configSideDetectors(const uint8_t* sfs, uint8_t num) {
     return getRadioDriver(_radio).configSideDetectors(sfs, num);
 }

zephcore/app/RoomServerMesh.h

@@ -212,6 +212,7 @@ public:
     void dumpLogFile() override;
     void setTxPower(int8_t power_dbm) override;
     bool setRxBoostedGain(bool enable) override;
+    bool setFemRxGain(bool enable) override;
     bool configSideDetectors(const uint8_t* sfs, uint8_t num) override;
     void formatNeighborsReply(char* reply) override;
     void formatStatsReply(char* reply) override;

zephcore/helpers/CommonCLI.cpp

@@ -544,6 +544,8 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
             snprintf(reply, CLI_REPLY_SIZE, "> %.6f", _prefs->node_lat);
         } else if (memcmp(config, "lon", 3) == 0) {
             snprintf(reply, CLI_REPLY_SIZE, "> %.6f", _prefs->node_lon);
+        } else if (memcmp(config, "radio.fem.rxgain", 16) == 0) {
+            snprintf(reply, CLI_REPLY_SIZE, "> %d", (int)_prefs->fem_rxgain);
         } else if (memcmp(config, "radio.rxgain", 12) == 0) {
             snprintf(reply, CLI_REPLY_SIZE, "> %d", (int)_prefs->rx_boost);
         } else if (memcmp(config, "radio", 5) == 0) {
@@ -1171,6 +1173,25 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
             } else {
                 strcpy(reply, "Error: unsupported by this board");
             }
+        } else if (memcmp(config, "radio.fem.rxgain ", 17) == 0) {
+            const char* arg = &config[17];
+            int val = -1;
+            if (memcmp(arg, "on", 2) == 0) val = 1;
+            else if (memcmp(arg, "off", 3) == 0) val = 0;
+            else if (arg[0] == '0' || arg[0] == '1') val = atoi(arg);
+            if (val == 0 || val == 1) {
+                /* Same shape as radio.rxgain: always save, then apply live and
+                 * report when the radio driver has no FEM gate. */
+                _prefs->fem_rxgain = (uint8_t)val;
+                savePrefs();
+                if (_callbacks->setFemRxGain(val == 1)) {
+                    snprintf(reply, CLI_REPLY_SIZE, "OK - radio.fem.rxgain=%d", _prefs->fem_rxgain);
+                } else {
+                    strcpy(reply, "Error: unsupported");
+                }
+            } else {
+                strcpy(reply, "Error: must be 0, 1, on, or off");
+            }
         } else if (memcmp(config, "radio.rxgain ", 13) == 0) {
             const char* arg = &config[13];
             int val = -1;

zephcore/helpers/CommonCLI.h

@@ -46,6 +46,10 @@ public:
     /* Apply RX boosted gain live; returns false when the radio has no
      * RX boost feature (upstream PR #2844 semantics). */
     virtual bool setRxBoostedGain(bool enable) { (void)enable; return false; }
+    /* Gate an external FEM/LNA in the RX direction, live.  Same semantics:
+     * false means the radio driver has no such knob.  On a supported radio
+     * whose board has no FEM wired it returns true and does nothing. */
+    virtual bool setFemRxGain(bool enable) { (void)enable; return false; }
     /* Configure LR2021 side detectors (multi-SF receive); num = 0 disables.
      * Returns false when the radio has no side detectors, or when the set
      * violates a chip constraint — the driver is the validator. */

zephcore/helpers/NodePrefs.h

@@ -93,6 +93,7 @@ struct NodePrefs {
 	float adc_multiplier;
 	char owner_info[120];
 	uint8_t rx_boost;               // 1 = boosted RX gain (+3dB), 0 = power save
+	uint8_t fem_rxgain;             // 1 = external FEM LNA active during RX, 0 = off (power save)
 	uint8_t rx_duty_cycle;          // 1 = RX duty cycle, 0 = continuous RX
 	/* RESERVED — formerly apc_enabled / apc_margin (Adaptive Power Control,
 	 * removed in 1.16.6). These two bytes are still read and written at their
@@ -217,6 +218,7 @@ static inline void sanitizeNodePrefs(NodePrefs* p) {
 	p->powersaving_enabled = saneBool<uint8_t>(p->powersaving_enabled, 0);
 	/* Defaults that are on, not off. */
 	p->rx_boost            = saneBool<uint8_t>(p->rx_boost, 1);
+	p->fem_rxgain          = saneBool<uint8_t>(p->fem_rxgain, 1);
 	p->wake_on_msg         = saneBool<uint8_t>(p->wake_on_msg, 1);
 	p->v_contact_enabled   = saneBool<uint8_t>(p->v_contact_enabled, 1);
 	/* Never let a corrupt byte take the radio off the air or hide BLE — both
@@ -302,6 +304,10 @@ static inline void initNodePrefs(NodePrefs* prefs) {
 	prefs->advert_loc_policy = ADVERT_LOC_NONE;
 	prefs->adc_multiplier = 0.0f;
 	prefs->rx_boost = 1;              // Default to boosted RX for better sensitivity
+	/* Default ON: the FEM's chip-enable has always been asserted for RX on the
+	 * boards that have one, so 1 is the historical behaviour and the only safe
+	 * default -- 0 costs the FEM's RX gain (~16 dB on SKY66122). */
+	prefs->fem_rxgain = 1;
 	prefs->rx_duty_cycle = 0;         // Default OFF — continuous RX for best reliability
 	prefs->_reserved_apc_enabled = 0; // reserved (was APC), see NodePrefs
 	prefs->_reserved_apc_margin = 0;  // reserved (was APC), see NodePrefs

zephcore/patches/zephyr-new/drivers/lora/native/sx126x/sx126x_ext.h

@@ -3,8 +3,8 @@
  * SX126x native driver — extension API
  *
  * Functions extending the standard Zephyr lora_driver_api with
- * SX126x-specific features (duty cycle, RX boost, RSSI readout,
- * preamble detection).
+ * SX126x-specific features (duty cycle, RX boost, external FEM gating,
+ * RSSI readout, preamble detection).
  */
 
 #ifndef SX126X_EXT_H
@@ -50,6 +50,26 @@ bool sx126x_is_receiving(const struct device *dev);
  */
 void sx126x_set_rx_boost(const struct device *dev, bool enable);
 
+/**
+ * @brief Enable/disable an external FEM's LNA in the RX direction
+ *
+ * Boards with an external front-end module wire its chip-enable to
+ * antenna-enable-gpios (KCT8103L CSD, SKY66122 CSD+CPS).  The driver normally
+ * asserts that line for both RX and TX.  Passing false withholds it for RX
+ * only: the FEM's LNA and its supply current (~6.5 mA on SKY66122) drop out,
+ * at the cost of the FEM's RX gain (~16 dB on the same part).  TX always
+ * asserts the line, and sleep/idle always clears it, so neither the transmit
+ * path nor the driver's idle gating is affected.
+ *
+ * Default is enabled.
+ *
+ * @param dev    LoRa device
+ * @param enable true to keep the FEM active during RX
+ * @return true if this board has an antenna-enable line to gate, false if it
+ *         has none (in which case the call did nothing)
+ */
+bool sx126x_set_fem_rx_enable(const struct device *dev, bool enable);
+
 /**
  * @brief Check if the radio chip is busy (cannot accept SPI commands)
  *

zephcore/patches/zephyr/0003-lora-sx126x-native.patch

@@ -38,10 +38,30 @@ top of upstream:
     C++ caller.  sx126x_lora_recv_async() has an idempotent fast path, so the
     failure-path startReceive() on that side is a no-op.
 
+  * External FEM/LNA RX gating -- sx126x_set_fem_rx_enable() plus the
+    fem_rx_off flag it sets.  antenna-enable-gpios is the chip-enable line of
+    the external FEM on the boards that route it there (KCT8103L CSD on
+    heltec_t096, heltec_wireless_tracker_v2 and heltec_wifi_lora32_v43;
+    GC1109 CSD on heltec_wifi_lora32_v4), and the driver asserts it for RX and
+    TX alike.  With the flag set, sx126x_set_rf_path() withholds it in the RX
+    direction only, so the FEM's LNA and its supply current drop out while TX
+    still gets the PA path and sleep/idle keeps clearing the line as before.
+    The setter returns false where the board declares no antenna-enable line,
+    so the CLI can report that rather than acknowledging a no-op -- that is
+    the rak3401_1watt case, where the SKY66122 enable is a standalone
+    regulator-boot-on rail outside the radio node.
+
+    The pin stays driver-owned throughout.  Taking it over from devicetree
+    instead would cost the idle gating, drop the ESP32 sleep-hold flags those
+    nodes carry, and on the boards whose CTX net is a separate tx-enable-gpios
+    it would desynchronise the external switch from DIO2.  Backs
+    `set radio.fem.rxgain` (default on = historical behaviour).
+
   * Extension API for the C++ adapter (sx126x_ext.h): sx126x_is_chip_busy,
-    sx126x_is_receiving, sx126x_set_rx_boost, sx126x_reset_agc,
-    sx126x_get_rssi_inst, sx126x_get_wakeup_time_us, the dc-restart counters,
-    the CAD tuning trio, and sx126x_apply_heltec_reg_patch.
+    sx126x_is_receiving, sx126x_set_rx_boost, sx126x_set_fem_rx_enable,
+    sx126x_reset_agc, sx126x_get_rssi_inst, sx126x_get_wakeup_time_us, the
+    dc-restart counters, the CAD tuning trio, and
+    sx126x_apply_heltec_reg_patch.
 
 In sx126x_hal.c, SX1262 Tx params use a measured-optimal PaConfig table indexed
 by requested power (RadioLib PR #1662) instead of the datasheet's fixed
@@ -1099,11 +1119,18 @@ index 30243ba5dc7..3a8bc017a52 100644
  }
  
  static void sx126x_set_rf_path(const struct device *dev, bool enable, bool tx)
-@@ -406,7 +900,20 @@ static void sx126x_set_rf_path(const struct device *dev, bool enable, bool tx)
+@@ -406,7 +900,26 @@ static void sx126x_set_rf_path(const struct device *dev, bool enable, bool tx)
  	const struct sx126x_hal_config *config = dev->config;
++	struct sx126x_data *data = dev->data;
  
- 	sx126x_hal_set_antenna_enable(dev, enable);
+-	sx126x_hal_set_antenna_enable(dev, enable);
 -	if (!config->dio2_tx_enable) {
++	/* An external FEM's enable line is asserted for TX unconditionally.  For
++	 * RX it follows fem_rx_off (the radio.fem.rxgain pref, applied through
++	 * sx126x_set_fem_rx_enable): clearing it drops the FEM's LNA and its
++	 * supply current, at the cost of that gain.  `enable` still wins, so
++	 * sleep and idle keep gating the line exactly as they did before. */
++	sx126x_hal_set_antenna_enable(dev, enable && (tx || !data->fem_rx_off));
 +	if (config->dio2_tx_enable) {
 +		/* DIO2 handles TX enable in hardware -- but rx-enable-gpios
 +		 * (e.g. E22-900M30S RXEN) and some board-specific tx-enable
@@ -1971,7 +1998,7 @@ index 30243ba5dc7..3a8bc017a52 100644
  	if (ret < 0) {
  		sx126x_set_sleep(dev);
  		k_mutex_unlock(&data->lock);
-@@ -1083,14 +2213,812 @@ static int sx126x_lora_test_cw(const struct device *dev, uint32_t frequency,
+@@ -1083,14 +2213,828 @@ static int sx126x_lora_test_cw(const struct device *dev, uint32_t frequency,
  	return 0;
  }
  
@@ -2126,6 +2153,22 @@ index 30243ba5dc7..3a8bc017a52 100644
 +	k_mutex_unlock(&data->lock);
 +}
 +
++bool sx126x_set_fem_rx_enable(const struct device *dev, bool enable)
++{
++	struct sx126x_data *data = dev->data;
++	const struct sx126x_hal_config *config = dev->config;
++
++	/* Stored inverted so the zero-initialised default is "FEM on in RX",
++	 * which is what the driver did before this knob existed.  No SPI and no
++	 * chip state: sx126x_set_rf_path() reads it on the next RX/TX/sleep
++	 * transition, and every RX (re)start passes through there. */
++	data->fem_rx_off = !enable;
++
++	/* False when the board wires no antenna-enable line: there is no FEM to
++	 * gate, so the caller can say so instead of acknowledging a no-op. */
++	return config->antenna_enable.port != NULL;
++}
++
 +void sx126x_reset_agc(const struct device *dev)
 +{
 +	struct sx126x_data *data = dev->data;
@@ -2837,7 +2880,7 @@ diff --git a/drivers/lora/native/sx126x/sx126x.h b/drivers/lora/native/sx126x/sx
 index 9dbf3f26586..b6df07ce7ab 100644
 --- a/drivers/lora/native/sx126x/sx126x.h
 +++ b/drivers/lora/native/sx126x/sx126x.h
-@@ -56,13 +56,96 @@ struct sx126x_data {
+@@ -56,13 +56,104 @@ struct sx126x_data {
  	/* Async RX callback */
  	lora_recv_cb rx_cb;
  	void *rx_cb_user_data;
@@ -2855,6 +2898,14 @@ index 9dbf3f26586..b6df07ce7ab 100644
 +	bool rx_duty_cycle_enabled;
 +	bool rx_boost_enabled;
 +
++	/* External FEM/LNA gating for the RX direction, set by
++	 * sx126x_set_fem_rx_enable().  Negative logic so the zero-initialised
++	 * default preserves the historical behaviour -- antenna-enable-gpios
++	 * asserted for both RX and TX.  When set, sx126x_set_rf_path() drops
++	 * the line for RX only: TX still asserts it and sleep/idle still
++	 * clears it, so the driver keeps sole ownership of the pin. */
++	bool fem_rx_off;
++
 +	/* AgcSensiAdjust value for the configured band (DS Table 6-4), cached
 +	 * because it shares register 0x08AC with the RX gain bits and so has
 +	 * to be re-applied by every RX-gain write.  Defaults to the 868-915

zephcore/src/main_companion.cpp

@@ -748,6 +748,10 @@ public:
 		return lora_radio.setRxBoost(enable);
 	}
 
+	bool setFemRxGain(bool enable) override {
+		return lora_radio.setFemRxEnable(enable);
+	}
+
 	bool configSideDetectors(const uint8_t* sfs, uint8_t num) override {
 		return lora_radio.configSideDetectors(sfs, num);
 	}
@@ -1589,6 +1593,7 @@ int main(void)
 
 	/* Apply RX boost and duty cycle from prefs */
 	lora_radio.setRxBoost(companion_mesh.prefs.rx_boost != 0);
+	lora_radio.setFemRxEnable(companion_mesh.prefs.fem_rxgain != 0);
 	lora_radio.enableRxDutyCycle(companion_mesh.prefs.rx_duty_cycle != 0);
 	lora_radio.setCadParams(companion_mesh.prefs.cad_auto != 0,
 				companion_mesh.prefs.cad_offset,

zephcore/src/main_repeater.cpp

@@ -745,6 +745,7 @@ int main(void)
 
 	/* Apply RX boost and duty cycle from prefs */
 	lora_radio.setRxBoost(prefs->rx_boost != 0);
+	lora_radio.setFemRxEnable(prefs->fem_rxgain != 0);
 	lora_radio.enableRxDutyCycle(prefs->rx_duty_cycle != 0);
 	lora_radio.setCadParams(prefs->cad_auto != 0, prefs->cad_offset,
 				prefs->probe_interval, prefs->cad_busycap);

zephcore/src/main_room_server.cpp

@@ -633,6 +633,7 @@ int main(void)
 
 	/* Apply RX boost and duty cycle from prefs */
 	lora_radio.setRxBoost(prefs->rx_boost != 0);
+	lora_radio.setFemRxEnable(prefs->fem_rxgain != 0);
 	lora_radio.enableRxDutyCycle(prefs->rx_duty_cycle != 0);
 	lora_radio.setCadParams(prefs->cad_auto != 0, prefs->cad_offset,
 				prefs->probe_interval, prefs->cad_busycap);