diff --git a/lib/fst4_decode.f90 b/lib/fst4_decode.f90
index 5d953e0e4..a4cce0dcd 100644
--- a/lib/fst4_decode.f90
+++ b/lib/fst4_decode.f90
@@ -64,7 +64,7 @@ contains
       integer naptypes(0:5,4)  ! (nQSOProgress,decoding pass)
       integer mcq(29),mrrr(19),m73(19),mrr73(19)
 
-      logical badsync,unpk77_success
+      logical badsync,unpk77_success,single_decode
       logical first,nohiscall,lwspr,ex
 
       integer*2 iwave(30*60*12000)
@@ -232,8 +232,13 @@ contains
 
       nhicoh=1
       nsyncoh=8
-      fa=max(100,nint(nfqso+1.5*baud-ntol))
-      fb=min(4800,nint(nfqso+1.5*baud+ntol))
+      fa=nfa
+      fb=nfb
+      single_decode=iand(nexp_decode,32).ne.0
+      if(single_decode) then
+         fa=max(100,nint(nfqso+1.5*baud-ntol))
+         fb=min(4800,nint(nfqso+1.5*baud+ntol))
+      endif
       minsync=1.20
       if(ntrperiod.eq.15) minsync=1.15
 
diff --git a/widgets/mainwindow.cpp b/widgets/mainwindow.cpp
index 6ff5351c2..99d42cb6a 100644
--- a/widgets/mainwindow.cpp
+++ b/widgets/mainwindow.cpp
@@ -3075,7 +3075,11 @@ void MainWindow::decode()                                       //decode()
     dec_data.params.ntol=20;
     dec_data.params.naggressive=0;
   }
-  if(m_mode=="FST4") dec_data.params.ntol=ui->sbFtol->value();
+  if(m_mode=="FST4") {
+    dec_data.params.ntol=ui->sbFtol->value();
+    dec_data.params.nfa=ui->sbF_Low->value();
+    dec_data.params.nfb=ui->sbF_High->value();
+  }
   if(m_mode=="FST4W") dec_data.params.ntol=ui->sbFST4W_FTol->value();
   if(dec_data.params.nutc < m_nutc0) m_RxLog = 1;       //Date and Time to file "ALL.TXT".
   if(dec_data.params.newdat==1 and !m_diskData) m_nutc0=dec_data.params.nutc;