diff --git a/src/atsc_app/inc/config.h b/src/atsc_app/inc/config.h
index 697aaf4..966bc40 100755
--- a/src/atsc_app/inc/config.h
+++ b/src/atsc_app/inc/config.h
@@ -45,6 +45,11 @@
 
 #define USE_UART_DEV_LINK           1
 
+/* IQ spectrum/eye-analysis periodic diagnostics on the debug UART.
+ * Keep disabled in normal operation; set to 1 only when timing/packet
+ * continuity troubleshooting is required. */
+#define IQ_ANALYSIS_UART_DEBUG       0
+
 /*
  * Prefer the local key/LCD path when the single-core CPU is busy with IQ
  * analysis.  Set to 0 to restore the original thread priorities.
diff --git a/src/atsc_app/task/iq_rx.c b/src/atsc_app/task/iq_rx.c
index ac27635..f7ae504 100755
--- a/src/atsc_app/task/iq_rx.c
+++ b/src/atsc_app/task/iq_rx.c
@@ -370,6 +370,7 @@ static void *iq_spec_thr(void *arg)
         }
 
         /* a full window is 26.21 ms = 1.08 ATSC fields; print only a short burst every 30s */
+#if IQ_ANALYSIS_UART_DEBUG
         {
             static time_t log_burst_start = 0;
             static int log_burst_count = 0;
@@ -386,6 +387,7 @@ static void *iq_spec_thr(void *arg)
                 log_burst_count++;
             }
         }
+#endif
         if (npkt == IQ_NPKT && ++nraw >= IQ_RAW_EVERY) {
             FILE *r = fopen("/tmp/iq_raw.bin", "wb");   /* whole contiguous window, for PC-side analysis */
             if (r) { fwrite(iq_win[buf], 1, IQ_WBYTES, r); fclose(r); }
diff --git a/src/atsc_app/task/iq_vsb.c b/src/atsc_app/task/iq_vsb.c
index 43470ec..07fd399 100755
--- a/src/atsc_app/task/iq_vsb.c
+++ b/src/atsc_app/task/iq_vsb.c
@@ -41,6 +41,7 @@
 #include <pthread.h>
 
 #include "iq_rx.h"
+#include "../inc/config.h"
 
 #ifndef M_PI
 #define M_PI 3.14159265358979323846
@@ -1395,6 +1396,7 @@ void iq_vsb_analyse(const unsigned char *win, int wid)
 
     minh = eyeh[0];
     for (j = 1; j < 7; j++) if (eyeh[j] < minh) minh = eyeh[j];
+#if IQ_ANALYSIS_UART_DEBUG
     printf("[iq_vsb] win %d: SNR %.2f dB (raw %.2f, ORx AGC jitter %.2f%%) tau %.4f theta %+.1f deg coff %+.3f Hz "
            "segsync %.1f@%d eye_w %.3f UI min_eye_h %.2f %s "
            "[ms: unpack %d tau %d demod %d stats %d eye %d total %d]\n",
@@ -1412,4 +1414,5 @@ void iq_vsb_analyse(const unsigned char *win, int wid)
     else
         printf("[pr12]   win %d: no field sync (ratio %.1f < %.1f), LEGACY fallback\n",
                wid, pr.ratio, PR12_RATIO_THR);
+#endif
 }
diff --git a/src/atsc_app/task/lcd_task.c b/src/atsc_app/task/lcd_task.c
index 9151980..c2bee4c 100755
--- a/src/atsc_app/task/lcd_task.c
+++ b/src/atsc_app/task/lcd_task.c
@@ -944,7 +944,7 @@ void get_tsnr_limd_uimd(uint16 *ptsnr, uint8 *plmid, uint8 *pumid)
 	// UIMD/LIMD and SNR now all come from the imx6's own 10 MSPS ORx window:
 	//   - LIMD/UIMD: iq_rx.c, same taps as the FPGA but band-averaged over 11 bins
 	//     and Welch-averaged. LIMD is the shoulder on the pilot's side. Half-dB units,
-	//     no +11 dB display offset (the web adds that).
+	//     displayed without the historical +11 dB offset.
 	//   - SNR: iq_vsb.c, the real 8VSB MER (I-path) of a demodulated window.
 	// If a source has not produced a fresh value we keep the previous one rather than
 	// report a fabricated number.
@@ -4215,11 +4215,11 @@ static void refresh_ad4(void *parg,void *parv)
 
     //需添加A:FSSI和B:FSSI ; FSSI 单源: update_fssi_state() 是唯一计算点,
     //本函数只读 st_extend_state.a_fssi/b_fssi 显示, 不再自己取数/换算。
-    //ab_flag=TRUE -> 当前选中 B 路(set_ab_switch(1)); FALSE -> A 路(set_ab_switch(0))。
+    //ab_flag=TRUE -> 逻辑/丝印 B；FALSE -> 逻辑/丝印 A，硬件位由统一映射转换。
     if(atsc_para.system_para.ab_mode==1)
     {
         if(check_delay_over(&tickbak,50)==TRUE)
-        { // 0x23 IQB_UPD: 1=B, 0=A (E_SELECT_A=0/E_SELECT_B=1)
+        { // 0x23 IQB_UPD: 逻辑A/B由 DPD_RF_SEL_VALUE() 映射到反向硬件位
             if(++ppara->ab_sec>16)
             {
                 ppara->ab_flag = ppara->ab_flag?FALSE:TRUE;
@@ -14533,14 +14533,24 @@ static void sec_proc_func(void)
 
 static void update_fssi_state(void)
 {
-    // 0x23 IQB_UPD: 1=B, 0=A (E_SELECT_A=0/E_SELECT_B=1)
+    // 0x23 IQB_UPD: 逻辑A/B由 DPD_RF_SEL_VALUE() 映射到反向硬件位
     uint8 a_fssi;
     uint8 b_fssi;
     uint8 data;
 
     static uint16 sec_cnt=0;
     static uint8  ab_flg =0;
+    static int    last_ab_mode = -1;
+    int           ab_mode = (atsc_para.system_para.ab_mode == 1);
 
+    /* FSSI Refresh alternates the ORx A/B path. IQ UDP windows can therefore
+     * contain both paths and must not be collected until Refresh is off.
+     * This edge check is intentionally before every early return below, so all
+     * configuration entry points take effect even while DPD is busy. */
+    if (ab_mode != last_ab_mode) {
+        iq_spec_set_enable(!ab_mode);
+        last_ab_mode = ab_mode;
+    }
 
     /*
         1. UPDATE and UPDLIN 返回
@@ -14800,7 +14810,7 @@ int sys_rf_agc_switch_proc(uint8 trigger)
 		//1 射频开关切换到A
 		u_dpdctl_r23.u8val = 0;
 		u_dpdctl_r23.dpd_bt.iqb_upd   = 0;
-		u_dpdctl_r23.dpd_bt.rf_sel    = 0; //A
+		u_dpdctl_r23.dpd_bt.rf_sel    = DPD_RF_SEL_VALUE(E_SELECT_A);
 		u_dpdctl_r23.dpd_bt.sync_mode = 0;
 		fpga_byte_write(0x05, FPGA_ADDR_DPD_IQB_UPD, u_dpdctl_r23.u8val);