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List:       gnuradio-discuss
Subject:    [Discuss-gnuradio] LFM Problems
From:       Michael Hill <mothic1 () gmail ! com>
Date:       2012-06-30 2:46:32
Message-ID: CAL8b5wuiYssEJbM2m14GkW_dna6pA0=37LT_086mxTLnQq59yw () mail ! gmail ! com
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I'm using GRC v 3.6.0 and looking at what can be done with the standard
library.


Although I've been able to apply FM to a wave, I'm still having issues
understanding how to manipulate the variables.
There is a Frequency Modulation block.. but i'm a bit confused about what
line 55
http://gnuradio.org/redmine/projects/gnuradio/repository/revisions/5d69a524f81f234b3fb \
c41d49ba18d6f6886baba/entry/gnuradio-core/src/lib/general/gr_frequency_modulator_fc.cc<http://gnuradio.org/doc/sphinx/gr/modulation_blk.html>


> From what I understand, to get Linear Frequency Modulation, I need a
parabolic change in phase.

d_phase = d_phase + d _sensitivity*in[i]

where (i believe)
d_sensitivity is set constant
and
in[i] is an input source of samples

> From what I gather from an earlier discussion thread if I put add a
sawtooth input then I should get a Linear Frequency response?
http://old.nabble.com/Generating-chrip-signals-td3985122.html

I appear to be getting a LFM, when i try feeding a Source [Sample Rate of
25M, Sawtooth wave,  Freq 1k, Ampl 1]  into a Frequency Modulation Block
[Sensitivity of 0.002]
but I'm unsure how to manipulate the inputs.

E.g. how would I set my values for d_sensitivity and amplitude to get my
LFM to shift from a frequency of 1000k to say 2000k?
Also, i'm a bit concerned that the sawtooth output doesn't appear to be
linear :/

Is there a better way of doing this using existing blocks?
Also what is the maths behind it.. i've just been beating my head against
the wall on this one and I appear to be just missing something

Please help!


<http://gnuradio.org/doc/sphinx/gr/modulation_blk.html>


[Attachment #3 (text/html)]

I&#39;m using GRC v 3.6.0 and looking at what can be done with the standard \
library.<br><br><br>Although I&#39;ve been able to apply FM to a wave, I&#39;m still \
having issues understanding how to manipulate the variables.<br> There is a Frequency \
Modulation block.. but i&#39;m a bit confused about what line 55<br> <a \
href="http://gnuradio.org/doc/sphinx/gr/modulation_blk.html" \
target="_blank">http://gnuradio.org/redmine/projects/gnuradio/repository/revisions/5d6 \
9a524f81f234b3fbc41d49ba18d6f6886baba/entry/gnuradio-core/src/lib/general/gr_frequency_modulator_fc.cc</a><br>
 <br>From what I understand, to get Linear Frequency Modulation, I need a parabolic \
change in phase.<br><br>d_phase = d_phase + d _sensitivity*in[i]   <br><br>where (i \
believe)<br>d_sensitivity is set constant<br>and<br>in[i] is an input source of \
samples<br> <br>From what I gather from an earlier discussion thread if I put add a \
sawtooth input then I should get a Linear Frequency response?<br><a \
href="http://old.nabble.com/Generating-chrip-signals-td3985122.html">http://old.nabble.com/Generating-chrip-signals-td3985122.html</a><br>
 <br>I appear to be getting a LFM, when i try feeding a Source [Sample Rate of 25M, \
Sawtooth wave,  Freq 1k,  Ampl 1]  into a Frequency Modulation Block [Sensitivity of \
0.002]<br>but I&#39;m unsure how to manipulate the inputs.<br><br>E.g. how would I \
set my values for d_sensitivity and amplitude to get my LFM to shift from a frequency \
of 1000k to say 2000k?<br> Also, i&#39;m a bit concerned that the sawtooth output \
doesn&#39;t appear to be linear :/<br><br>Is there a better way of doing this using \
existing blocks?<br>Also what is the maths behind it.. i&#39;ve just been beating my \
head against the wall on this one and I appear to be just missing something<br> \
<br>Please help!<br><br><br><a \
href="http://gnuradio.org/doc/sphinx/gr/modulation_blk.html" target="_blank"></a>



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