From c52f755afc498b880bfdf7ca00c0c73f2c35ffff Mon Sep 17 00:00:00 2001
From: Steve Franke <s.j.franke@icloud.com>
Date: Fri, 25 Jan 2019 16:26:13 -0600
Subject: [PATCH] Make Watterson simulator causal.

---
 lib/ft8/watterson.f90 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ft8/watterson.f90 b/lib/ft8/watterson.f90
index fc3dca113..7c3aa35d3 100644
--- a/lib/ft8/watterson.f90
+++ b/lib/ft8/watterson.f90
@@ -47,7 +47,7 @@ subroutine watterson(c,npts,nsig,fs,delay,fspread)
 
   nshift=nint(0.001*delay*fs)
   if(delay.gt.0.0) then
-     c2(0:npts-1)=cshift(c(0:npts-1),nshift)
+     c2(0:npts-1)=cshift(c(0:npts-1),-nshift) !negative shifts are right shifts
   else
      c2(0:npts-1)=0.0
   endif