diff --git a/CMakeLists.txt b/CMakeLists.txt
index 83100946f..9565c5060 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -411,6 +411,7 @@ set (wsjt_FSRCS
   lib/ft8/encode174_91.f90
   lib/entail.f90
   lib/ephem.f90
+  lib/77bit/exch_valid.f90
   lib/extract.f90
   lib/extract4.f90
   lib/extractmessage144.f90
diff --git a/lib/77bit/exch_valid.f90 b/lib/77bit/exch_valid.f90
new file mode 100644
index 000000000..70613fc9a
--- /dev/null
+++ b/lib/77bit/exch_valid.f90
@@ -0,0 +1,61 @@
+logical*1 function exch_valid(ntype,exch)
+  
+  parameter (NSEC=84)      !Number of ARRL Sections
+  parameter (NUSCAN=65)    !Number of US states and Canadian provinces
+
+  character*(*) exch
+  character*3 c3
+  character*3 cmult(NUSCAN)
+  character*3 csec(NSEC)
+
+  data csec/                                                         &
+       "AB ","AK ","AL ","AR ","AZ ","BC ","CO ","CT ","DE ","EB ",  &       
+       "EMA","ENY","EPA","EWA","GA ","GTA","IA ","ID ","IL ","IN ",  &       
+       "KS ","KY ","LA ","LAX","MAR","MB ","MDC","ME ","MI ","MN ",  &       
+       "MO ","MS ","MT ","NC ","ND ","NE ","NFL","NH ","NL ","NLI",  &       
+       "NM ","NNJ","NNY","NT ","NTX","NV ","OH ","OK ","ONE","ONN",  &       
+       "ONS","OR ","ORG","PAC","PR ","QC ","RI ","SB ","SC ","SCV",  &       
+       "SD ","SDG","SF ","SFL","SJV","SK ","SNJ","STX","SV ","TN ",  &       
+       "UT ","VA ","VI ","VT ","WCF","WI ","WMA","WNY","WPA","WTX",  &       
+       "WV ","WWA","WY ","DX "/
+  data cmult/                                                        &
+       "AL ","AK ","AZ ","AR ","CA ","CO ","CT ","DE ","FL ","GA ",  &
+       "HI ","ID ","IL ","IN ","IA ","KS ","KY ","LA ","ME ","MD ",  &
+       "MA ","MI ","MN ","MS ","MO ","MT ","NE ","NV ","NH ","NJ ",  &
+       "NM ","NY ","NC ","ND ","OH ","OK ","OR ","PA ","RI ","SC ",  &
+       "SD ","TN ","TX ","UT ","VT ","VA ","WA ","WV ","WI ","WY ",  &
+       "NB ","NS ","QC ","ON ","MB ","SK ","AB ","BC ","NWT","NF ",  &
+       "LB ","NU ","YT ","PEI","DC "/
+
+  exch_valid=.false.
+  n=len(trim(exch))
+  if(ntype.ne.3 .and. ntype.ne.4) go to 900
+  if(ntype.eq.3 .and. (n.lt.2 .or. n.gt.7)) go to 900
+  if(ntype.eq.4 .and. (n.lt.2 .or. n.gt.3)) go to 900
+  
+  if(ntype.eq.3) then                   !Field Day
+     i1=index(exch,' ')
+     if(i1.lt.3) go to 900
+     read(exch(1:i1-2),*,err=900) ntx
+     if(ntx.lt.1 .or. ntx.gt.32) go to 900
+     if(exch(i1-1:i1-1).lt.'A' .or. exch(i1-1:i1-1).gt.'F') go to 900
+     c3=exch(i1+1:)//'   '
+     do i=1,NSEC
+        if(csec(i).eq.c3) then
+           exch_valid=.true.
+           go to 900
+        endif
+     enddo
+     
+  else if(ntype.eq.4) then              !RTTY Roundup
+     c3=exch//' '
+     do i=1,NUSCAN
+        if(cmult(i).eq.c3) then
+           exch_valid=.true.
+           go to 900
+        endif
+     enddo
+  endif
+
+900 return
+end function exch_valid