## Copyright (C) 2018 Jens Ahrensfeld
## 
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or
## (at your option) any later version.
## 
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## 
## You should have received a copy of the GNU General Public License
## along with this program.  If not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*- 
## @deftypefn {Function File} {@var{retval} =} qdemod_eval (@var{input1}, @var{input2})
##
## @seealso{}
## @end deftypefn

## Author: Jens Ahrensfeld <ahrensfeld@w2ess001vm>
## Created: 2018-11-16

function qdemod_eval

fa = 1000;
T = 1/fa;
N = 1000

t = (0:N-1)*T;

omega_x_0 = 100.0;
omega_x_1 = 200.0;
phi_x = pi/8*0;

omega_lo = 150.0;


lo_r = cos(2*pi*omega_lo*t);
lo_i = sin(2*pi*omega_lo*t);

x = cos(2*pi*omega_x_0*t + phi_x) + cos(2*pi*omega_x_1*t + phi_x);
y = x.*lo_r + x.*lo_i*i;

subplot(2,1,1);
plot(t, y, t, x); grid;
subplot(2,1,2);
Y = fftshift(fft(y, N))/N;
X = fftshift(fft(x, N))/N;
f = (-length(X)/2:length(X)/2-1)/N*fa;
plot(f, abs(X), f, abs(Y)); grid;

endfunction