WSJT-X/lib/ft4/genft4.f90
Steve Franke 71cb6d9f50 Use 4 different Costas arrays to prevent false syncs as received frames move
through the analysis window.

Add a random 77-bit vector to each message so that tone transitions occur
even if the message contains a long string of 0 or 1 (like a CQ).

Add alternative sync calculation as an option (sync2), for testing.

Add basic framework for AP decoding.
2019-02-05 19:18:50 -06:00

83 lines
2.1 KiB
Fortran

subroutine genft4(msg0,ichk,msgsent,i4tone)
! Encode an FT4 message
! Input:
! - msg0 requested message to be transmitted
! - ichk if ichk=1, return only msgsent
! - msgsent message as it will be decoded
! - i4tone array of audio tone values, {0,1,2,3}
! Frame structure:
! s16 + 87symbols + 2 ramp up/down = 105 total channel symbols
! r1 + s4 + d29 + s4 + d29 + s4 + d29 + s4 + r1
! Message duration: TxT = 105*512/12000 = 4.48 s
! use iso_c_binding, only: c_loc,c_size_t
use packjt77
include 'ft4_params.f90'
character*37 msg0
character*37 message !Message to be generated
character*37 msgsent !Message as it will be received
character*77 c77
integer*4 i4tone(NN),itmp(ND)
integer*1 codeword(2*ND)
integer*1 msgbits(77),rvec(77)
integer icos4a(4),icos4b(4),icos4c(4),icos4d(4)
logical unpk77_success
data icos4a/0,1,3,2/
data icos4b/1,0,2,3/
data icos4c/2,3,1,0/
data icos4d/3,2,0,1/
data rvec/0,1,0,0,1,0,1,0,0,1,0,1,1,1,1,0,1,0,0,0,1,0,0,1,1,0,1,1,0, &
1,0,0,1,0,1,1,0,0,0,0,1,0,0,0,1,0,1,0,0,1,1,1,1,0,0,1,0,1, &
0,1,0,1,0,1,1,0,1,1,1,1,1,0,0,0,1,0,1/
message=msg0
do i=1, 37
if(ichar(message(i:i)).eq.0) then
message(i:37)=' '
exit
endif
enddo
do i=1,37 !Strip leading blanks
if(message(1:1).ne.' ') exit
message=message(i+1:)
enddo
i3=-1
n3=-1
call pack77(message,i3,n3,c77)
call unpack77(c77,0,msgsent,unpk77_success) !Unpack to get msgsent
if(ichk.eq.1) go to 999
read(c77,"(77i1)") msgbits
msgbits=mod(msgbits+rvec,2)
call encode174_91(msgbits,codeword)
! Grayscale mapping:
! bits tone
! 00 0
! 01 1
! 11 2
! 10 3
do i=1,ND
is=codeword(2*i)+2*codeword(2*i-1)
if(is.le.1) itmp(i)=is
if(is.eq.2) itmp(i)=3
if(is.eq.3) itmp(i)=2
enddo
i4tone(1:4)=icos4a
i4tone(5:33)=itmp(1:29)
i4tone(34:37)=icos4b
i4tone(38:66)=itmp(30:58)
i4tone(67:70)=icos4c
i4tone(71:99)=itmp(59:87)
i4tone(100:103)=icos4d
999 return
end subroutine genft4