Hello
I am trying to represent with MATLAB, from the processing of the IQ values in a *.iq file recorded with SPIKE, the values of ‘IQ vs. Time ‘, ‘ AM vs Time ‘, ‘ PM vs Time ‘ and ‘ FM vs Time ‘. In the process I have had the following difficulties:
1. The values of the IQ data read from the recorded file of an X signal, differ from the values of the same signal but acquired directly using the bbgetiq () function.
2. The values of the parameters’ IQ vs. Time ‘, ‘ AM vs Time ‘, ‘ PM vs Time ‘ and ‘ FM vs Time ‘. calculated and represented with MATLAB, differ from the values represented by the SPIKE software in the reproduction of the same .iq file.
I am attaching the code in order to find out which error I am making.
Thanks for the help
% SCRIPT IQ signal representation recorded with SPIKE software.
clear variables;
% clear functions;
%% ADD TEMPORARY FOLDERS
addpath('SxIQ_REC');% Folder where the * .iq and * .xml files are located
%% PARAMETERS
fDir='IQREC-Test1';
%IQ file of recordings with Signal Hound BB60A
fDir_iq=[fDir '.iq'];
fDir_xml=[fDir '.xml'];
%% Reading XML file.
iqXMLDoc= xmlread(fDir_xml);
%<CenterFrequency>
CenterFrequency_List = (iqXMLDoc.getElementsByTagName('CenterFrequency'));
CeFr = str2double(CenterFrequency_List.item(0).getFirstChild.getData);
%<SampleRate>
SampleRate_List = (iqXMLDoc.getElementsByTagName('SampleRate'));
SaRa = str2double(SampleRate_List.item(0).getFirstChild.getData);
%<Decimation>
Decimation_List = (iqXMLDoc.getElementsByTagName('Decimation'));
Dec = str2double(Decimation_List.item(0).getFirstChild.getData);
%<ScaleFactor>
ScaleFactor_List = (iqXMLDoc.getElementsByTagName('ScaleFactor'));
ScFa= str2double(ScaleFactor_List.item(0).getFirstChild.getData);
%% Reading and processing of the .iq file
f=fopen(fDir_iq,'r');
s=fread(f,'int16');
n=length(s)/2;
iq = reshape(s, 2, n);% Transform s into a two-row, n-column matrix.
vSh = iq(1,:) + 1i * iq(2,:);% Form the complex signal .
%2) Convert 16-bit integer max scaled values to floating point values between -1 and 1.
ScBin=2^16/2;
vSh=vSh/ScBin;
% 3) Multiply by the scale factor that the XML file has
vSh=vSh*ScFa;
vI = real(vSh);
vQ = imag(vSh);
% % Calculate the power of the samples in dBm
% vS_dBm=10*log10(vI.^2+vQ.^2);
%% GRAPHICS
iqdata = vSh;% Vector containing the complex values of the IQ signal
iqlen=length(iqdata);%
iqdata = transpose(iqdata);% perform the transpose
Ts=1/SaRa;
subplot(2,2,1);
am = 10.0 * log10(abs(iqdata).^2);
plot(am);
title('AM vs Time');
xlabel('Sample number');
ylabel('Amplitude (dBm)');
%
subplot(2,2,3);
x = linspace(1, iqlen, iqlen);
plot(x, real(iqdata), x, imag(iqdata));
title('IQ vs. Time');
xlabel('Sample number');
ylabel('Amplitude ()');
subplot(2,2,2);
pm=atan2(imag(iqdata),real(iqdata));
dg_pm= diff ([0;pm]);% [0;pm] so that dg_pm has the same values as pm
fm=dg_pm*(SaRa/(2*pi));
plot(fm/1e6);
title('FM vs Time');
xlabel('Sample number');
ylabel('Frequency (MHz)');
axis([0,length(x),-inf,inf]);
subplot(2,2,4);
plot(pm);
title('PM vs Time');
xlabel('Sample number');
ylabel('Phase');
axis([0,length(x),-inf,inf]);
%%
rmpath('SxIQ_REC');% Delete the folder in the MATLAB paths