mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-10-30 20:40:28 -04:00
48 lines
1.2 KiB
Fortran
48 lines
1.2 KiB
Fortran
subroutine fspread_lorentz(cdat,fspread)
|
|
|
|
parameter (NZ=3*12000)
|
|
complex cdat(0:NZ-1)
|
|
complex cspread(0:NZ-1)
|
|
complex z
|
|
|
|
twopi=8.0*atan(1.0)
|
|
nfft=NZ
|
|
nh=nfft/2
|
|
df=12000.0/nfft
|
|
cspread(0)=1.0
|
|
cspread(nh)=0.
|
|
b=6.0 !Use truncated Lorenzian shape for fspread
|
|
do i=1,nh
|
|
f=i*df
|
|
x=b*f/fspread
|
|
z=0.
|
|
a=0.
|
|
if(x.lt.3.0) then !Cutoff beyond x=3
|
|
a=sqrt(1.111/(1.0+x*x)-0.1) !Lorentzian amplitude
|
|
phi1=twopi*rran() !Random phase
|
|
z=a*cmplx(cos(phi1),sin(phi1))
|
|
endif
|
|
cspread(i)=z
|
|
z=0.
|
|
if(x.lt.3.0) then !Same thing for negative freqs
|
|
phi2=twopi*rran()
|
|
z=a*cmplx(cos(phi2),sin(phi2))
|
|
endif
|
|
cspread(nfft-i)=z
|
|
enddo
|
|
|
|
call four2a(cspread,nfft,1,1,1) !Transform to time domain
|
|
|
|
sum=0.
|
|
do i=0,nfft-1
|
|
p=real(cspread(i))**2 + aimag(cspread(i))**2
|
|
sum=sum+p
|
|
enddo
|
|
avep=sum/nfft
|
|
fac=sqrt(1.0/avep)
|
|
cspread=fac*cspread !Normalize to constant avg power
|
|
cdat=cspread*cdat !Apply Rayleigh fading
|
|
|
|
return
|
|
end subroutine fspread_lorentz
|