diff --git a/lib/fst4/fst4sim.f90 b/lib/fst4/fst4sim.f90
index 83ac5baed..28caf2fe0 100644
--- a/lib/fst4/fst4sim.f90
+++ b/lib/fst4/fst4sim.f90
@@ -120,7 +120,7 @@ program fst4sim
       if(fspread.gt.0.0 .or. delay.ne.0.0) call watterson(c,nwave,NZ,fs,delay,fspread)
       if(fspread.lt.0.0) call lorentzian_fading(c,nwave,fs,-fspread)
       c=sig*c
-      wave=real(c)
+      wave=aimag(c)
       if(snrdb.lt.90) then
          do i=1,nmax                   !Add gaussian noise at specified SNR
             xnoise=gran()
diff --git a/lib/fst4/gen_fst4wave.f90 b/lib/fst4/gen_fst4wave.f90
index ead00709b..74a9b34c9 100644
--- a/lib/fst4/gen_fst4wave.f90
+++ b/lib/fst4/gen_fst4wave.f90
@@ -1,91 +1,93 @@
 subroutine gen_fst4wave(itone,nsym,nsps,nwave,fsample,hmod,f0,    &
-     icmplx,cwave,wave)
+   icmplx,cwave,wave)
 
-  parameter(NTAB=65536)
-  real wave(nwave)
-  complex cwave(nwave),ctab(0:NTAB-1)
-  real, allocatable, save :: pulse(:)
-  real, allocatable :: dphi(:)
-  integer hmod
-  integer itone(nsym)
-  logical first
-  data first/.true./
-  data nsps0/-99/
-  save first,twopi,dt,tsym,nsps0,ctab
+   use prog_args
+   parameter(NTAB=65536)
+   real wave(nwave)
+   complex cwave(nwave),ctab(0:NTAB-1)
+   character(len=1) :: cvalue 
+   real, allocatable, save :: pulse(:)
+   real, allocatable :: dphi(:)
+   integer hmod
+   integer itone(nsym)
+   logical first, lshape
+   data first/.true./
+   data nsps0/-99/
+   data lshape/.true./
+   save first,twopi,dt,tsym,nsps0,ctab,lshape
 
-  if(first) then
-     twopi=8.0*atan(1.0)
-     do i=0,NTAB-1
-        phi=i*twopi/NTAB
-        ctab(i)=cmplx(cos(phi),sin(phi))
-     enddo
-  endif
+   if(first) then
+      twopi=8.0*atan(1.0)
+      do i=0,NTAB-1
+         phi=i*twopi/NTAB
+         ctab(i)=cmplx(cos(phi),sin(phi))
+      enddo
+      call get_environment_variable("FST4_NOSHAPING",cvalue,nlen)
+      if(nlen.eq.1 .and. cvalue.eq."1") lshape=.false.
+   endif
 
-  if(first.or.nsps.ne.nsps0) then
-     if(allocated(pulse)) deallocate(pulse)
-     allocate(pulse(1:3*nsps))
-     dt=1.0/fsample
-     tsym=nsps/fsample
+   if(first.or.nsps.ne.nsps0) then
+      if(allocated(pulse)) deallocate(pulse)
+      allocate(pulse(1:3*nsps))
+      dt=1.0/fsample
+      tsym=nsps/fsample
 ! Compute the smoothed frequency-deviation pulse
-     do i=1,3*nsps
-        tt=(i-1.5*nsps)/real(nsps)
-        pulse(i)=gfsk_pulse(2.0,tt)
-     enddo
-     first=.false.
-     nsps0=nsps
-  endif
+      do i=1,3*nsps
+         tt=(i-1.5*nsps)/real(nsps)
+         pulse(i)=gfsk_pulse(2.0,tt)
+      enddo
+      first=.false.
+      nsps0=nsps
+   endif
 
 ! Compute the smoothed frequency waveform.
 ! Length = (nsym+2)*nsps samples, zero-padded
-  allocate( dphi(0:(nsym+2)*nsps-1) )
-  dphi_peak=twopi*hmod/real(nsps)
-  dphi=0.0 
-  do j=1,nsym        
-     ib=(j-1)*nsps
-     ie=ib+3*nsps-1
-     dphi(ib:ie) = dphi(ib:ie) + dphi_peak*pulse(1:3*nsps)*itone(j)
-  enddo
+   allocate( dphi(0:(nsym+2)*nsps-1) )
+   dphi_peak=twopi*hmod/real(nsps)
+   dphi=0.0
+   do j=1,nsym
+      ib=(j-1)*nsps
+      ie=ib+3*nsps-1
+      dphi(ib:ie) = dphi(ib:ie) + dphi_peak*pulse(1:3*nsps)*itone(j)
+   enddo
 
 ! Calculate and insert the audio waveform
-  phi=0.0
-  dphi = dphi + twopi*(f0-1.5*hmod/tsym)*dt       !Shift frequency up by f0
-  if(icmplx.eq.0) wave=0.
-  if(icmplx.eq.1) cwave=0.
-  k=0
-  do j=0,(nsym+2)*nsps-1
-     k=k+1
-     i=phi*float(NTAB)/twopi
-     i=iand(i,NTAB-1)
-     if(icmplx.eq.0) then
-        wave(k)=real(ctab(i))
-     else
-        cwave(k)=ctab(i)
-     endif
-     phi=phi+dphi(j)
-     if(phi.gt.twopi) phi=phi-twopi
-  enddo
+   phi=0.0
+   dphi = dphi + twopi*(f0-1.5*hmod/tsym)*dt       !Shift frequency up by f0
+   if(icmplx.eq.0) wave=0.
+   if(icmplx.eq.1) cwave=0.
+   k=0
+   do j=nsps,(nsym+1)*nsps-1
+      k=k+1
+      i=phi*float(NTAB)/twopi
+      i=iand(i,NTAB-1)
+      if(icmplx.eq.0) then
+         wave(k)=aimag(ctab(i))
+      else
+         cwave(k)=ctab(i)
+      endif
+      phi=phi+dphi(j)
+      if(phi.gt.twopi) phi=phi-twopi
+   enddo
 
 ! Compute the ramp-up and ramp-down symbols
-  kshift=nsps
-  if(icmplx.eq.0) then
-     wave(1:nsps)=0.0
-     wave(nsps+1:nsps+nsps/4)=wave(nsps+1:nsps+nsps/4) *                      &
-          (1.0-cos(twopi*(/(i,i=0,nsps/4-1)/)/real(nsps/2)))/2.0
-     k1=nsym*nsps+3*nsps/4+1
-     wave((nsym+1)*nsps+1:)=0.0 
-     wave(k1:k1+nsps/4)=wave(k1:k1+nsps/4) *                              &
-          (1.0+cos(twopi*(/(i,i=0,nsps/4)/)/real(nsps/2)))/2.0
-     wave=cshift(wave,kshift)
-  else
-     cwave(1:nsps)=0.0
-     cwave(nsps+1:nsps+nsps/4)=cwave(nsps+1:nsps+nsps/4) *                    &
-          (1.0-cos(twopi*(/(i,i=0,nsps/4-1)/)/real(nsps/2)))/2.0
-     k1=nsym*nsps+3*nsps/4+1
-     cwave((nsym+1)*nsps+1:)=0.0
-     cwave(k1:k1+nsps/4)=cwave(k1:k1+nsps/4) *                              &
-          (1.0+cos(twopi*(/(i,i=0,nsps/4)/)/real(nsps/2)))/2.0
-     cwave=cshift(cwave,kshift)
-  endif
+   if(icmplx.eq.0) then
+      if(lshape) then
+         wave(1:nsps/4)=wave(1:nsps/4) *                      &
+            (1.0-cos(twopi*(/(i,i=0,nsps/4-1)/)/real(nsps/2)))/2.0
+         k1=(nsym-1)*nsps+3*nsps/4+1
+         wave(k1:k1+nsps/4)=wave(k1:k1+nsps/4) *                              &
+            (1.0+cos(twopi*(/(i,i=0,nsps/4)/)/real(nsps/2)))/2.0
+      endif
+   else
+      if(lshape) then
+         cwave(1:nsps/4)=cwave(1:nsps/4) *                    &
+            (1.0-cos(twopi*(/(i,i=0,nsps/4-1)/)/real(nsps/2)))/2.0
+         k1=(nsym-1)*nsps+3*nsps/4+1
+         cwave(k1:k1+nsps/4)=cwave(k1:k1+nsps/4) *                              &
+            (1.0+cos(twopi*(/(i,i=0,nsps/4)/)/real(nsps/2)))/2.0
+      endif
+   endif
 
-  return
+   return
 end subroutine gen_fst4wave