diff --git a/.gitignore b/.gitignore
index 93c41db2..197fc73a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
+# Local machine configuration (not shared)
+CLAUDE.local.md
+
 # ESP32 firmware build artifacts and local config (contains WiFi credentials)
 firmware/esp32-csi-node/build/
 firmware/esp32-csi-node/sdkconfig
diff --git a/firmware/esp32-csi-node/main/Kconfig.projbuild b/firmware/esp32-csi-node/main/Kconfig.projbuild
index 609dc2d4..245d023d 100644
--- a/firmware/esp32-csi-node/main/Kconfig.projbuild
+++ b/firmware/esp32-csi-node/main/Kconfig.projbuild
@@ -39,4 +39,18 @@ menu "CSI Node Configuration"
         help
             WiFi channel to listen on for CSI data.
 
+    config CSI_FILTER_MAC
+        string "CSI source MAC filter (AA:BB:CC:DD:EE:FF or empty)"
+        default ""
+        help
+            When set to a valid MAC address (e.g. "AA:BB:CC:DD:EE:FF"),
+            only CSI frames from that transmitter are processed. All
+            other frames are silently dropped. This prevents signal
+            mixing in multi-AP environments.
+
+            Leave empty to accept CSI from all transmitters.
+
+            Can be overridden at runtime via NVS key "filter_mac"
+            (6-byte blob) without reflashing.
+
 endmenu
diff --git a/firmware/esp32-csi-node/main/csi_collector.c b/firmware/esp32-csi-node/main/csi_collector.c
index 4ce95b53..aaed5d92 100644
--- a/firmware/esp32-csi-node/main/csi_collector.c
+++ b/firmware/esp32-csi-node/main/csi_collector.c
@@ -26,6 +26,15 @@ static uint32_t s_sequence = 0;
 static uint32_t s_cb_count = 0;
 static uint32_t s_send_ok = 0;
 static uint32_t s_send_fail = 0;
+static uint32_t s_filtered = 0;
+
+/* ---- MAC address filter (Issue #98) ---- */
+
+/** When non-zero, only CSI from s_filter_mac is accepted. */
+static uint8_t s_filter_enabled = 0;
+
+/** The accepted transmitter MAC address (6 bytes). */
+static uint8_t s_filter_mac[6] = {0};
 
 /* ---- ADR-029: Channel-hop state ---- */
 
@@ -124,18 +133,52 @@ size_t csi_serialize_frame(const wifi_csi_info_t *info, uint8_t *buf, size_t buf
     return frame_size;
 }
 
+void csi_collector_set_filter_mac(const uint8_t *mac)
+{
+    if (mac == NULL) {
+        s_filter_enabled = 0;
+        memset(s_filter_mac, 0, 6);
+        ESP_LOGI(TAG, "MAC filter disabled — accepting CSI from all transmitters");
+    } else {
+        memcpy(s_filter_mac, mac, 6);
+        s_filter_enabled = 1;
+        ESP_LOGI(TAG, "MAC filter enabled: only accepting %02X:%02X:%02X:%02X:%02X:%02X",
+                 mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
+    }
+    s_filtered = 0;
+}
+
 /**
  * WiFi CSI callback — invoked by ESP-IDF when CSI data is available.
+ *
+ * When a MAC filter is active, frames from non-matching transmitters are
+ * silently dropped to prevent signal mixing in multi-AP environments.
  */
 static void wifi_csi_callback(void *ctx, wifi_csi_info_t *info)
 {
     (void)ctx;
     s_cb_count++;
 
+    /* ---- MAC address filter (Issue #98) ---- */
+    if (s_filter_enabled) {
+        if (memcmp(info->mac, s_filter_mac, 6) != 0) {
+            s_filtered++;
+            if (s_filtered <= 3 || (s_filtered % 500) == 0) {
+                ESP_LOGD(TAG, "Filtered CSI from %02X:%02X:%02X:%02X:%02X:%02X (dropped %lu)",
+                         info->mac[0], info->mac[1], info->mac[2],
+                         info->mac[3], info->mac[4], info->mac[5],
+                         (unsigned long)s_filtered);
+            }
+            return;
+        }
+    }
+
     if (s_cb_count <= 3 || (s_cb_count % 100) == 0) {
-        ESP_LOGI(TAG, "CSI cb #%lu: len=%d rssi=%d ch=%d",
+        ESP_LOGI(TAG, "CSI cb #%lu: len=%d rssi=%d ch=%d mac=%02X:%02X:%02X:%02X:%02X:%02X",
                  (unsigned long)s_cb_count, info->len,
-                 info->rx_ctrl.rssi, info->rx_ctrl.channel);
+                 info->rx_ctrl.rssi, info->rx_ctrl.channel,
+                 info->mac[0], info->mac[1], info->mac[2],
+                 info->mac[3], info->mac[4], info->mac[5]);
     }
 
     uint8_t frame_buf[CSI_MAX_FRAME_SIZE];
diff --git a/firmware/esp32-csi-node/main/csi_collector.h b/firmware/esp32-csi-node/main/csi_collector.h
index 47c8ef13..5aeef1bc 100644
--- a/firmware/esp32-csi-node/main/csi_collector.h
+++ b/firmware/esp32-csi-node/main/csi_collector.h
@@ -22,12 +22,28 @@
 /** Maximum number of channels in the hop table (ADR-029). */
 #define CSI_HOP_CHANNELS_MAX 6
 
+/** Length of a MAC address in bytes. */
+#define CSI_MAC_LEN 6
+
 /**
  * Initialize CSI collection.
  * Registers the WiFi CSI callback.
  */
 void csi_collector_init(void);
 
+/**
+ * Set a MAC address filter for CSI collection.
+ *
+ * When set, only CSI frames from the specified transmitter MAC are processed;
+ * all others are silently dropped. This prevents signal mixing in multi-AP
+ * environments.
+ *
+ * Pass NULL to disable filtering (accept CSI from all transmitters).
+ *
+ * @param mac  6-byte MAC address to accept, or NULL to disable filtering.
+ */
+void csi_collector_set_filter_mac(const uint8_t *mac);
+
 /**
  * Serialize CSI data into ADR-018 binary frame format.
  *
diff --git a/firmware/esp32-csi-node/main/main.c b/firmware/esp32-csi-node/main/main.c
index 23c2867a..5652fd9b 100644
--- a/firmware/esp32-csi-node/main/main.c
+++ b/firmware/esp32-csi-node/main/main.c
@@ -134,6 +134,13 @@ void app_main(void)
     /* Initialize CSI collection */
     csi_collector_init();
 
+    /* Apply MAC address filter if configured (Issue #98) */
+    if (s_cfg.filter_mac_enabled) {
+        csi_collector_set_filter_mac(s_cfg.filter_mac);
+    } else {
+        ESP_LOGI(TAG, "No MAC filter — accepting CSI from all transmitters");
+    }
+
     ESP_LOGI(TAG, "CSI streaming active → %s:%d",
              s_cfg.target_ip, s_cfg.target_port);
 
diff --git a/firmware/esp32-csi-node/main/nvs_config.c b/firmware/esp32-csi-node/main/nvs_config.c
index dd549f6a..a8452cf3 100644
--- a/firmware/esp32-csi-node/main/nvs_config.c
+++ b/firmware/esp32-csi-node/main/nvs_config.c
@@ -9,6 +9,7 @@
 #include "nvs_config.h"
 
 #include <string.h>
+#include <stdio.h>
 #include "esp_log.h"
 #include "nvs_flash.h"
 #include "nvs.h"
@@ -51,6 +52,29 @@ void nvs_config_load(nvs_config_t *cfg)
     cfg->tdm_slot_index = 0;
     cfg->tdm_node_count = 1;
 
+    /* MAC filter: default disabled (all zeros) */
+    memset(cfg->filter_mac, 0, 6);
+    cfg->filter_mac_enabled = 0;
+
+    /* Parse compile-time Kconfig MAC filter if set (format: "AA:BB:CC:DD:EE:FF") */
+#ifdef CONFIG_CSI_FILTER_MAC
+    {
+        const char *mac_str = CONFIG_CSI_FILTER_MAC;
+        unsigned int m[6];
+        if (mac_str[0] != '\0' &&
+            sscanf(mac_str, "%x:%x:%x:%x:%x:%x",
+                   &m[0], &m[1], &m[2], &m[3], &m[4], &m[5]) == 6) {
+            for (int i = 0; i < 6; i++) {
+                cfg->filter_mac[i] = (uint8_t)m[i];
+            }
+            cfg->filter_mac_enabled = 1;
+            ESP_LOGI(TAG, "Kconfig MAC filter: %02X:%02X:%02X:%02X:%02X:%02X",
+                     cfg->filter_mac[0], cfg->filter_mac[1], cfg->filter_mac[2],
+                     cfg->filter_mac[3], cfg->filter_mac[4], cfg->filter_mac[5]);
+        }
+    }
+#endif
+
     /* Try to override from NVS */
     nvs_handle_t handle;
     esp_err_t err = nvs_open("csi_cfg", NVS_READONLY, &handle);
@@ -152,6 +176,27 @@ void nvs_config_load(nvs_config_t *cfg)
         }
     }
 
+    /* MAC filter (stored as a 6-byte blob in NVS key "filter_mac") */
+    uint8_t mac_blob[6];
+    size_t mac_len = 6;
+    if (nvs_get_blob(handle, "filter_mac", mac_blob, &mac_len) == ESP_OK && mac_len == 6) {
+        /* Check it's not all zeros (which would mean "no filter") */
+        uint8_t is_zero = 1;
+        for (int i = 0; i < 6; i++) {
+            if (mac_blob[i] != 0) { is_zero = 0; break; }
+        }
+        if (!is_zero) {
+            memcpy(cfg->filter_mac, mac_blob, 6);
+            cfg->filter_mac_enabled = 1;
+            ESP_LOGI(TAG, "NVS override: filter_mac=%02X:%02X:%02X:%02X:%02X:%02X",
+                     mac_blob[0], mac_blob[1], mac_blob[2],
+                     mac_blob[3], mac_blob[4], mac_blob[5]);
+        } else {
+            cfg->filter_mac_enabled = 0;
+            ESP_LOGI(TAG, "NVS override: filter_mac disabled (all zeros)");
+        }
+    }
+
     /* Validate tdm_slot_index < tdm_node_count */
     if (cfg->tdm_slot_index >= cfg->tdm_node_count) {
         ESP_LOGW(TAG, "tdm_slot_index=%u >= tdm_node_count=%u, clamping to 0",
diff --git a/firmware/esp32-csi-node/main/nvs_config.h b/firmware/esp32-csi-node/main/nvs_config.h
index 87e0a0c3..8779585d 100644
--- a/firmware/esp32-csi-node/main/nvs_config.h
+++ b/firmware/esp32-csi-node/main/nvs_config.h
@@ -35,6 +35,10 @@ typedef struct {
     uint32_t dwell_ms;                        /**< Dwell time per channel in ms. */
     uint8_t  tdm_slot_index;                  /**< This node's TDM slot index (0-based). */
     uint8_t  tdm_node_count;                  /**< Total nodes in the TDM schedule. */
+
+    /* MAC address filter for CSI source selection (Issue #98) */
+    uint8_t  filter_mac[6];                   /**< Transmitter MAC to accept (all zeros = no filter). */
+    uint8_t  filter_mac_enabled;              /**< 1 = filter active, 0 = accept all. */
 } nvs_config_t;
 
 /**