sweeping, phase continous and streaming

[Jieyi]

Hi,

I would like to refer you to http://forums.ni.com/ni/board/message?board.id=310&thread.id=1015&view=by_date_ascending&page=2

I have try the method done by Kalyan. It can sweep upwards using the Chirp method. 

But is there a way which I can sweep the frequency up and down while monitoring the phase, eg:

LL - Low Frequency, HF - High Frequcency, SF - Start Frequency, CF - Center Frequency

It will start from SF, then sweep up to HF, then sweep down to LL, then up CF.

Beside generating the Chirp waveform to do the sweeping, is there any other alternative?

End of the day, I will generate a large chunk of data for streaming.

[hoffiz]

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.

Message Edited by Jaime F on 12-07-2007 04:15 PM

[Jieyi]

Hi,

I have merge the “create chirp” into the niFgen_OSP_Advanced_Example.vi. 

But it don't seems to be able to sweep the frequency downwards.  Once it hit the Upper limit, i can see that, it immedialtly drop down to the Lower Limit.

Is there anything wrong with my program?

[kalyanramuv]

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

[Fuh]

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

[hoffiz]

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.

[Fuh]

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.

[hoffiz]

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.

[Fuh]

Thanks a lot.

Fuh