WSJT-X/fil6521.f

45 lines
1.4 KiB
Fortran

subroutine fil6521(c1,n1,c2,n2)
C FIR lowpass filter designed using ScopeFIR
C Pass #1 Pass #2
C-----------------------------------------------
C fsample (Hz) 1378.125 Input sample rate
C Ntaps 21 Number of filter taps
C fc (Hz) 40 Cutoff frequency
C fstop (Hz) 172.266 Lower limit of stopband
C Ripple (dB) 0.1 Ripple in passband
C Stop Atten (dB) 38 Stopband attenuation
C fout (Hz) 344.531 Output sample rate
parameter (NTAPS=21)
parameter (NH=NTAPS/2)
parameter (NDOWN=4) !Downsample ratio = 1/4
complex c1(n1)
complex c2(n1/NDOWN)
C 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
C 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