diff --git a/NANOVNA_STM32_F303/mcuconf.h b/NANOVNA_STM32_F303/mcuconf.h
index 7fb7543..92cc42b 100644
--- a/NANOVNA_STM32_F303/mcuconf.h
+++ b/NANOVNA_STM32_F303/mcuconf.h
@@ -75,6 +75,12 @@
 /*
  * RTC driver system settings for stm32f303
  */
+#define RTC_PRER(a, s)              ((((a) - 1) << 16) | ((s) - 1))
+
+// LSE for 32768 quartz
+#define STM32_RTC_LSE_PRER                  RTC_PRER(128,  256)
+// LSI 40k
+#define STM32_RTC_LSI_PRER                  RTC_PRER( 40, 1000)
 
 #ifndef VNA_USE_LSE
 // Use 40kHz LSI
diff --git a/halconf.h b/halconf.h
index 251afec..b3767eb 100644
--- a/halconf.h
+++ b/halconf.h
@@ -122,7 +122,7 @@
  * @brief   Enables the RTC subsystem.
  */
 #if !defined(HAL_USE_RTC) || defined(__DOXYGEN__)
-#define HAL_USE_RTC                 TRUE
+#define HAL_USE_RTC                 FALSE
 #endif
 
 /**
diff --git a/main.c b/main.c
index 293c41b..6c1dbf5 100644
--- a/main.c
+++ b/main.c
@@ -2890,7 +2890,12 @@ int main(void)
 {
   halInit();
   chSysInit();
-
+ /*
+  * Initialize RTC library (not used ChibiOS RTC module)
+  */
+  #ifdef __USE_RTC__
+    rtc_init();
+  #endif
   //palSetPadMode(GPIOB, 8, PAL_MODE_ALTERNATE(1) | PAL_STM32_OTYPE_OPENDRAIN);
   //palSetPadMode(GPIOB, 9, PAL_MODE_ALTERNATE(1) | PAL_STM32_OTYPE_OPENDRAIN);
 #ifdef __VNA__
diff --git a/rtc.c b/rtc.c
index dc83882..80c771a 100644
--- a/rtc.c
+++ b/rtc.c
@@ -26,7 +26,7 @@
 
 // Compact STM32 RTC time library
 #if HAL_USE_RTC == TRUE
-//#error "Error VNA use self RTC lib, define HAL_USE_RTC = FALSE in halconf.h"
+#error "Error VNA use self RTC lib, define HAL_USE_RTC = FALSE in halconf.h"
 #endif
 
 // Get RTC time as binary structure in 0x00HHMMSS