diff --git a/sa_core.c b/sa_core.c
index a40eb69..d2b51ac 100644
--- a/sa_core.c
+++ b/sa_core.c
@@ -2900,6 +2900,7 @@ common_silent:
     break;
   case TP_30MHZ:
     set_mode(M_LOW);
+    maxFreq = 520000000;            // needed to measure the LPF rejection
     set_refer_output(0);
  //   set_step_delay(1);                      // Do not set !!!!!
 #ifdef __SPUR__