diff --git a/fivehz.f90 b/fivehz.f90
index 32130fdae..df9950f62 100644
--- a/fivehz.f90
+++ b/fivehz.f90
@@ -209,3 +209,21 @@ subroutine fivehztx
   endif
   return
 end subroutine fivehztx
+
+subroutine addnoise(n)
+  integer*2 n
+  real r(12)
+  include 'gcom1.f90'
+
+  if(txsnrdb.gt.90.0) return
+  snr=10.0**(0.05*(txsnrdb-1))
+  call random_number(r)
+  x=sum(r)-6.0
+  i=3000.0*x + n*snr*3000.0/32768.0
+  if(i>32767) i=32767;
+  if(i<-32767) i=-32767;
+  n=i
+
+  return
+end subroutine addnoise
+
diff --git a/gcom1.f90 b/gcom1.f90
index 0ffc26b0c..e9515b5bd 100644
--- a/gcom1.f90
+++ b/gcom1.f90
@@ -11,6 +11,7 @@ real*8 rxdelay         !Delay between PTT=1 and Tx audio        SoundIn
 real*8 txdelay         !Delay from end of Tx Audio and PTT=0    SoundOut
 real*8 samfacin        !(Input sample rate)/11025               GUI
 real*8 samfacout       !(Output sample rate)/11025              GUI
+real*8 txsnrdb         !SNR for simulations                     GUI
 integer*2 y1           !Ring buffer for audio channel 0         SoundIn
 integer*2 y2           !Ring buffer for audio channel 1         SoundIn
 integer nmax           !Actual length of Rx ring buffers        GUI
@@ -41,7 +42,7 @@ integer mfsample2      !Measured sample rate, output            SoundOut
 integer ns0            !Time at last ALL.TXT date entry         Decoder
 
 common/gcom1/Tbuf(1024),ntrbuf(1024),Tsec,rxdelay,txdelay,              &
-     samfacin,samfacout,y1(NRXMAX),y2(NRXMAX),                          &
+     samfacin,samfacout,txsnrdb,y1(NRXMAX),y2(NRXMAX),                  &
      nmax,iwrite,iread,iwave(NTXMAX),nwave,TxOK,Receiving,Transmitting, &
      TxFirst,TRPeriod,ibuf,ibuf0,ave,rms,ngo,level,mute,newdat,ndsec,   &
      ndevin,ndevout,nx,mfsample,mfsample2,ns0
diff --git a/jtaudio.c b/jtaudio.c
index 0df7a9808..1d17b4036 100644
--- a/jtaudio.c
+++ b/jtaudio.c
@@ -137,6 +137,7 @@ static int SoundOut( void *inputBuffer, void *outputBuffer,
   short *in = (short*)inputBuffer;
   short *wptr = (short*)outputBuffer;
   unsigned int i,n;
+  static short n2;
   static int n0;
   static int ia=0;
   static int ib=0;
@@ -167,6 +168,7 @@ static int SoundOut( void *inputBuffer, void *outputBuffer,
 
   for(i=0 ; i<framesPerBuffer; i++ )  {
     if(*data->TxOK)  {
+      addnoise_(&data->iwave[ic]);
       *wptr++ = data->iwave[ic];        //left
       *wptr++ = data->iwave[ic];        //right
       ic++;
@@ -177,8 +179,10 @@ static int SoundOut( void *inputBuffer, void *outputBuffer,
       }
     }
     else {
-      *wptr++ = 0;                     //left
-      *wptr++ = 0;                     //right
+      n2=0;
+      addnoise_(&n2);
+      *wptr++ = n2;                     //left
+      *wptr++ = n2;                     //right
     }
   }
   fivehztx_();                             //Call fortran routine
diff --git a/wsjt.py b/wsjt.py
index 02371599a..8eed72d75 100644
--- a/wsjt.py
+++ b/wsjt.py
@@ -86,6 +86,7 @@ setseq=IntVar()
 ShOK=IntVar()
 slabel="Sync   "
 textheight=7
+txsnrdb=99.
 TxFirst=IntVar()
 green=zeros(500,'f')
 im=Image.new('P',(500,120))
@@ -892,6 +893,9 @@ def clear_avg(event=NONE):
     avetext.configure(state=NORMAL)
     avetext.delete('1.0',END)
     avetext.configure(state=DISABLED)
+    f=open(appdir+'/decoded.ave',mode='w')
+    f.truncate(0)                           #Delete contents of decoded.ave
+    f.close()
     Audio.gcom2.nclearave=1
 
 #------------------------------------------------------ defaults
@@ -1225,7 +1229,7 @@ def plot_yellow():
 def update():
     global root_geom,isec0,naz,nel,ndmiles,ndkm,nhotaz,nhotabetter,nopen, \
            im,pim,cmap0,isync,isync441,isync6m,isync65,isync_save,idsec, \
-           first,itol
+           first,itol,txsnrdb
     
     utc=time.gmtime(time.time()+0.1*idsec)
     isec=utc[5]
@@ -1335,6 +1339,16 @@ def update():
     tx4.configure(bg='white')
     tx5.configure(bg='white')
     tx6.configure(bg='white')
+    if tx6.get()[:1]=='#':
+        try:
+            txsnrdb=float(tx6.get()[1:])
+            if txsnrdb>-99.0 and txsnrdb<10.0:
+                Audio.gcom1.txsnrdb=txsnrdb
+                tx6.configure(bg='orange')
+        except:
+            txsnrdb=99.0
+    else:
+        txsnrdb=99.0
     if Audio.gcom2.monitoring and not Audio.gcom1.transmitting:
         bmonitor.configure(bg='green')
     else:
@@ -1347,8 +1361,9 @@ def update():
 #        t="Transmitting:  "
 #        t="Txing:  "+t[:nmsg]
         bgcolor='yellow'
-        if Audio.gcom2.sendingsh==1:  bgcolor='#66FFFF'
-        if Audio.gcom2.sendingsh==-1: bgcolor='red'
+        if Audio.gcom2.sendingsh==1:  bgcolor='#66FFFF'    #Shorthand
+        if Audio.gcom2.sendingsh==-1: bgcolor='red'        #Plain Text
+        if txsnrdb<90.0: bgcolor='orange'                  #Simulation mode
         if Audio.gcom2.ntxnow==1: tx1.configure(bg=bgcolor)
         elif Audio.gcom2.ntxnow==2: tx2.configure(bg=bgcolor)
         elif Audio.gcom2.ntxnow==3: tx3.configure(bg=bgcolor)