From b3f0aec4075fc0ff995b63256971b017fa255ced Mon Sep 17 00:00:00 2001
From: Joe Taylor <joe@princeton.edu>
Date: Fri, 30 Oct 2020 14:52:58 -0400
Subject: [PATCH] Q65: compute snr from esnodb, using actual symbol rate.

---
 lib/qra/q65/q65_loops.f90 | 7 ++++---
 lib/qra/q65/q65_subs.c    | 8 ++++----
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/lib/qra/q65/q65_loops.f90 b/lib/qra/q65/q65_loops.f90
index 8fef412d4..f476ce0fc 100644
--- a/lib/qra/q65/q65_loops.f90
+++ b/lib/qra/q65/q65_loops.f90
@@ -69,7 +69,7 @@ subroutine q65_loops(c00,npts2,nsps,mode,mode64,nsubmode,nFadingModel,   &
               ncall=ncall+1
               call timer('qra64_de',0)
               call q65_intrinsics_ff(s3,nsubmode,b90,nFadingModel,s3prob)
-              call q65_dec(s3,s3prob,APmask,APsymbols,snr2,dat4,irc)
+              call q65_dec(s3,s3prob,APmask,APsymbols,esnodb,dat4,irc)
               ! irc > 0 ==> number of iterations required to decode
               !  -1 = invalid params
               !  -2 = decode failed
@@ -84,8 +84,7 @@ subroutine q65_loops(c00,npts2,nsps,mode,mode64,nsubmode,nFadingModel,   &
         a(1)=-f0
         call twkfreq(c00,c0,npts2,6000.0,a)
         jpk=3000                       !###  These definitions need work ###
-!       if(nsps.ge.3600) jpk=4080      !###
-        if(nsps.ge.3600) jpk=6000      !###
+        if(nsps.ge.3600) jpk=6000      !###  TR >= 60 s
         call spec64(c0,nsps,mode,mode64,jpk,s3,LL,NN)
         call pctile(s3,LL*NN,40,base)
         s3=s3/base
@@ -100,6 +99,8 @@ subroutine q65_loops(c00,npts2,nsps,mode,mode64,nsubmode,nFadingModel,   &
 
   if(irc.ge.0) then
      navg=nsave
+     baud=6000.0/nsps
+     snr2=esnodb - db(2500.0/baud)
      if(iavg.eq.0) navg=0
      !### For tests only:
      open(53,file='fort.53',status='unknown',position='append')
diff --git a/lib/qra/q65/q65_subs.c b/lib/qra/q65/q65_subs.c
index ffd4c0385..b36adc540 100644
--- a/lib/qra/q65/q65_subs.c
+++ b/lib/qra/q65/q65_subs.c
@@ -77,14 +77,14 @@ void q65_intrinsics_ff_(float s3[], int* submode, float* B90,
 }
 		
 void q65_dec_(float s3[], float s3prob[], int APmask[], int APsymbols[],
-	      float* snr2500, int xdec[], int* rc0)
+	      float* esnodb0, int xdec[], int* rc0)
 {
 
 /* Input:   s3prob[LL,NN]   Symbol-value intrinsic probabilities
  *          APmask[13]      AP information to be used in decoding
  *          APsymbols[13]   Available AP informtion
  * Output:  
- *          snr2500         SNR_2500 of decoded signal, or lower limit
+ *          esnodb0         Estimated Es/No in dB
  *          xdec[13]        Decoded 78-bit message as 13 six-bit integers
  *          rc0             Return code from q65_decode()
  */
@@ -98,7 +98,7 @@ void q65_dec_(float s3[], float s3prob[], int APmask[], int APsymbols[],
   // rc = -1:  Invalid params
   // rc = -2:  Decode failed
   // rc = -3:  CRC mismatch
-  *snr2500 = -31.0;
+  *esnodb0 = 0.0;             //Default Es/No for a failed decode
   if(rc<0) return;
 
   rc = q65_esnodb_fastfading(&codec,&esnodb,ydec,s3);
@@ -106,5 +106,5 @@ void q65_dec_(float s3[], float s3prob[], int APmask[], int APsymbols[],
     printf("error in q65_esnodb_fastfading()\n");
     exit(0);
   }
-  *snr2500 = esnodb - 31.0;
+  *esnodb0 = esnodb;
 }