How do I generate the I(n) & Q(n) values from an X(n) value. The X(n) are the input data between -1 and 1. The variables are related using X(n) = I(n) + j*Q(n). I need these values to calculate the instantaneous frequency using freq = Fs * delta(atan(q/i)) / 2*pi. Thanks,
generating I & Q
Started by ●March 11, 2005
Reply by ●March 11, 20052005-03-11
Reply by ●March 11, 20052005-03-11
"Neo" <zingafriend@yahoo.com> wrote in message news:1110524418.550458.275210@g14g2000cwa.googlegroups.com...> In = Xn*cos(theta) > Qn=Xn*sin(theta) >and theta = n*2*pi/fs + some arbitrary constant if you like. Best of luck - Mike
Reply by ●March 11, 20052005-03-11
<george_barr@yahoo.com> wrote in message news:1110516798.705729.115930@o13g2000cwo.googlegroups.com...> How do I generate the I(n) & Q(n) values from an X(n) value. The X(n) > are the input data between -1 and 1. The variables are related using > X(n) = I(n) + j*Q(n). I need these values to calculate the > instantaneous frequency using freq = Fs * delta(atan(q/i)) / 2*pi. > > Thanks, >If you samples are indeed real, try using the HILBERT function to convert is to an anlytic signal, so you can use the ANGLE function on the complex samples. -Aj
Reply by ●March 11, 20052005-03-11
Neo wrote:> In = Xn*cos(theta) > Qn=Xn*sin(theta)Ah so! How should George find theta? Atan(Q/I)? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 11, 20052005-03-11
in article 3cmdnVQNj5o0RKzfRVn-tg@rcn.net, Jerry Avins at jya@ieee.org wrote on 03/11/2005 12:47:> Neo wrote: >> In = Xn*cos(theta) >> Qn=Xn*sin(theta) > > Ah so! How should George find theta? Atan(Q/I)?which is good for I > 0. strictly speaking it's arg{I + j*Q} or atan2(Q, I) if your computer has that one. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●March 12, 20052005-03-12
I am still having trouble creating my Matlab m-file. I am trying to
find the instantaneous FM frequency of a signal for the purpose of FM
demodulation. I tried atan() and atan2() without successful results.
Here is my m-file. If the program below works, it should print out the
Fi or 200Hz. Can someone help me with this?
function result = fm_iq04
format long;
Fs = 1000; % Number of samples
Fc = 250; % center freq
Fi = 200; % Frequency of interest
Ts = 1 / Fs;
t = Ts*(0:Fs-1)';
x = cos(2*pi*Fi*t);
cur_a = 0;
last_a = 0;
for i = 1:length(x) - 1
theta = (i * 2 * pi) / Fs;
cur_i = x(i) * cos(theta);
cur_q = x(i) * sin(theta);
cur_a = atan2(cur_q, cur_i);
% cur_a = atan(cur_q / cur_i);
freq = (Fs * (cur_a - last_a)) / 2 * pi;
% display the instantaneous frequency
disp(freq);
last_a = cur_a;
end
Thanks,
Reply by ●March 12, 20052005-03-12
I figured it out. I can use the hilbert() matlab function to convert a
real signal into a complex signal. Here is the m-file to compute the
instantaneous frequency and it seems to work.
function result = fm_iq09
format long;
Fs = 5000; % Number of samples
Fc = 1250; % center freq
Fi = 1570; % Frequency of interest
Ts = 1 / Fs;
t = Ts*(0:Fs-1)';
x = cos(2*pi*Fi*t);
x = hilbert(x);
cur_a = 0;
last_a = 0;
for i = 1:length(x) - 1
cur_i = real(x(i));
cur_q = imag(x(i));
cur_a = atan(cur_q / cur_i);
freq = (Fs * (cur_a - last_a)) / 2 * pi / 10;
error = (Fi / freq) - 1;
if freq > 0
disp(freq);
disp(error);
end
last_a = cur_a;
end
Reply by ●March 12, 20052005-03-12
in article 1110613336.330448.148760@f14g2000cwb.googlegroups.com, george_barr@yahoo.com at george_barr@yahoo.com wrote on 03/12/2005 02:42:> I figured it out. I can use the hilbert() matlab function to convert a > real signal into a complex signal. Here is the m-file to compute the > instantaneous frequency and it seems to work.i think you still have phase unwrapping issues to work out. if you don't want to explicitly unwrap your phase angle, perhaps you want to compute your phase difference with a trig identity that i can't remember. it's for arctan(q[n]/i[n]) - arctan(q[n-1]/i[n-1]) = something if you find that identity and use it for phase difference (which is proportional to frequency), you won't have to worry about unwrapping. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●March 14, 20052005-03-14
This is a multi-part message in MIME format. --------------000706080404020207000004 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit robert bristow-johnson wrote:>in article 1110613336.330448.148760@f14g2000cwb.googlegroups.com, >george_barr@yahoo.com at george_barr@yahoo.com wrote on 03/12/2005 02:42: > > > >>I figured it out. I can use the hilbert() matlab function to convert a >>real signal into a complex signal. Here is the m-file to compute the >>instantaneous frequency and it seems to work. >> >> > >i think you still have phase unwrapping issues to work out. if you don't >want to explicitly unwrap your phase angle, perhaps you want to compute your >phase difference with a trig identity that i can't remember. it's for > > arctan(q[n]/i[n]) - arctan(q[n-1]/i[n-1]) = something > >if you find that identity and use it for phase difference (which is >proportional to frequency), you won't have to worry about unwrapping. > > >in Matlab following formula works also (signal must be complex): freq = Fs/2/pi * diff( unwrap (imag (log (signal)))); Ren� --------------000706080404020207000004 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1"> <title></title> </head> <body text="#000000" bgcolor="#ffffff"> robert bristow-johnson wrote:<br> <blockquote type="cite" cite="midBE58DB51.5343%25rbj@audioimagination.com"> <pre wrap="">in article <a class="moz-txt-link-abbreviated" href="mailto:1110613336.330448.148760@f14g2000cwb.googlegroups.com">1110613336.330448.148760@f14g2000cwb.googlegroups.com</a>, <a class="moz-txt-link-abbreviated" href="mailto:george_barr@yahoo.com">george_barr@yahoo.com</a> at <a class="moz-txt-link-abbreviated" href="mailto:george_barr@yahoo.com">george_barr@yahoo.com</a> wrote on 03/12/2005 02:42: </pre> <blockquote type="cite"> <pre wrap="">I figured it out. I can use the hilbert() matlab function to convert a real signal into a complex signal. Here is the m-file to compute the instantaneous frequency and it seems to work. </pre> </blockquote> <pre wrap=""><!----> i think you still have phase unwrapping issues to work out. if you don't want to explicitly unwrap your phase angle, perhaps you want to compute your phase difference with a trig identity that i can't remember. it's for arctan(q[n]/i[n]) - arctan(q[n-1]/i[n-1]) = something if you find that identity and use it for phase difference (which is proportional to frequency), you won't have to worry about unwrapping. </pre> </blockquote> <tt>in Matlab following formula works also (signal must be complex):<br> <br> freq = Fs/2/pi * diff( unwrap (imag (log (signal))));<br> <br> René<br> </tt> </body> </html> --------------000706080404020207000004--
