12-06-2007 11:52 AM
12-07-2007 04:11 PM - edited 12-07-2007 04:15 PM
Hi Jieyi,
For the waveform to be phase continuous it does need to be a chirp. Another option is to build a waveform that will have chunks of different frequencies, this is call a Frequency List Mode, if you go the NI Signal Generator Help and search for: “Frequency List Mode 5441” you will found a very good explanation of what Frequency list is. The 5441 has 5 mode of operation Standard Function, Arbitrary Waveform; this is the one used in Kalyan example, Arbitrary Sequence, Script and Frequency List. Agian the difference between these modes is in the "NI Signal Generator Help".
For your first question I don’t see any problem for doing a ('up-chirp') or decreases ('down-chirp'), at the end you are building a ramp to change Wx, If you want to go back to the Carrier frequency you will have to build something like a "triangle" instead of a “ramp”, I have attach the modified “create chirp” that will help you accomplish the down- chirp.
12-09-2007 10:24 PM
12-10-2007 12:11 PM
Hi Jieyi,
I want to explain the concept behind chirp generation using 5441 little bit before I provide the answer for your question.
I am using FM Signal Concept to generated chirp signals.
Let's say that we want to sweep from 100kHz to 500kHz. The Center frequency of this Signal would be the mean (100+500)kHz/2=300kHz. The frequency deviation = (500-100)/2=200kHz.
To sweep from 100kHz to 500kHz, we would need a ramp signal to indicate the FM Signal generation VI that we intend to sweep. 100kHz would correspond to a value of -1 in FM Index and 500kHz would correspond to factor of 1 in FM Index. In simple words, to sweep from 100kHz to 500kHz we need to create a ramp signal from -1 to 1. To sweep from 300kHz to 500kHz, we would create a ramp signal from 0 to 1 for the given center frequency of 300kHz and Frequency Deviation of 200kHz.
The formula for this factor is (Frequency to be generated - Center Frequency)/ Frequency Deviation.
To create the frequency profiles needed, you would have combine multiple ramp profiles and use the FM Signal VI to generate necessary signal.
The attached zip file has VI's shdemonstrates this concept. Frequency Sweep Profile (Main).vi is the main VI. I have used Spectrogram VI's in this example. If you don't Advanced Signal Processing Toolkit installed on your computer, you will not find these VI's. In this case, I would recommend you delete the spectrogram VI's from blockdiagram and run the main VI.
I understand that I posted lot of information. Let me know if I am not clear on anything...
Thanks,
Kalyan
07-01-2008 10:31 AM
Dear Jaime,
I am using DAQCard 6062E and Labview 8.0. I need to generate a frequency sweep, linearly sweeping from 10 to 100 Hz and then linearly sweeping back to 10 Hz, similar to what you did for Yieyi. However, the file "Create Chirp Wave.vi" you created requires a newer Labview version to open. Can you be kind enough to post this VI again with a version that can be opened using Labview 8.0?
Thanks a lot in advance for your kindness and help.
Fuh
07-02-2008 10:42 AM
Hi Fuh,
The VIs that you are looking at the screen shoot are the same in LabVIEW 8.0 for what you are trying to do, the function is called “ramp pattern.vi” , basically you are going to construct the array with the sample needed. I won’t be able to save the code as a previous version since due to the drivers used but you don’t need anything else.
07-02-2008 01:34 PM
Dear Jaime,
Thank you so much for your quick response and comments. I used the "chirp pattern" function and created a frequency sweep going up and down. However, for my application, I need to start the signal with an amplitude of one, instead of zero. Or I should say, the signal needs to start with an initial phase of 90 degrees, instead of zero degrees. Is there a way to accomplish this?
Best wishes,
Fuh
Attached is a simple vi I created for this purpose.
07-07-2008 12:56 PM
Hi Fuh,
You have complete freedom on the array. Remember that at the
end you are simply build and array that you can modify and change however you
want. You can manually delete the first
couple of samples until your array has the 90 degrees offset.
I hope it helps.
07-07-2008 05:51 PM
Thanks a lot.
Fuh