WSJT-X/map65/libm65/fil6521.f90

45 lines
1.4 KiB
Fortran

subroutine fil6521(c1,n1,c2,n2)
! FIR lowpass filter designed using ScopeFIR
! Pass #1 Pass #2
!-----------------------------------------------
! fsample (Hz) 1378.125 Input sample rate
! Ntaps 21 Number of filter taps
! fc (Hz) 40 Cutoff frequency
! fstop (Hz) 172.266 Lower limit of stopband
! Ripple (dB) 0.1 Ripple in passband
! Stop Atten (dB) 38 Stopband attenuation
! fout (Hz) 344.531 Output sample rate
parameter (NTAPS=21)
parameter (NH=(NTAPS-1)/2)
parameter (NDOWN=4) !Downsample ratio = 1/4
complex c1(n1)
complex c2(n1/NDOWN)
! Filter coefficients:
real a(-NH:NH)
data a/ &
-0.011958606980,-0.013888627387,-0.015601306443,-0.010602249570, &
0.003804023436, 0.028320058273, 0.060903935217, 0.096841904411, &
0.129639871228, 0.152644580853, 0.160917511283, 0.152644580853, &
0.129639871228, 0.096841904411, 0.060903935217, 0.028320058273, &
0.003804023436,-0.010602249570,-0.015601306443,-0.013888627387, &
-0.011958606980/
n2=(n1-NTAPS+NDOWN)/NDOWN
k0=NH-NDOWN+1
! Loop over all output samples
do i=1,n2
c2(i)=0.
k=k0 + NDOWN*i
do j=-NH,NH
c2(i)=c2(i) + c1(j+k)*a(j)
enddo
enddo
return
end subroutine fil6521