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AM Waveform of AWG

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AM Waveform of AWG

Postby jom » Mon Aug 02, 2010 1:50 am

I'm trying to come up with an AM modulated waveform in Excel for the AWG. For the life of me I can't figure it out. I need 1 kHz tones riding along with a 455 kHz carrier. The confusion I think has something to do with what to set the Picoscope frequency generator at once you import the waveform. Since I don't know quite what to use I'm having a difficult time generating it in Excel.

Thanks

jom
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Re: AM Waveform of AWG

Postby jom » Mon Aug 02, 2010 8:09 pm

I got a bit farther today. I was able to get an AM generated wave out of a spice simulator. I cut it down to 8192 samples.

However, what I see on the PS is a jumbled mess. I verified the waveform itself in the simulator AND in a graph in excel. It "looks" right. But when I bring it into the AWG it's not even remotely close. What should I use as the frequency choice given it's a 1 kHz wave riding on 455 kHz?

Any help would be appreciated...

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Re: AM Waveform of AWG

Postby ziko » Wed Aug 04, 2010 10:00 am

Hi Jom,

Could you send the waveform file and what it is supposed to look like? Also what scope are you using?

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Re: AM Waveform of AWG

Postby jom » Wed Aug 04, 2010 6:29 pm

I was able to attach a graph of what it should look like. However, the .cvs file I made won't attach to this post for some reason. (???)

Anyway, I generated this waveform in SPICE and was able to place the data in a .csv. I was also able to import this into PS. However for some reason I do not understand it requires putting in 250 Hz as the "frequency". The spectrum is a mess though...

Ideally the spectrum should be a tone at 455 kHz with two smaller tones at +/- 1 kHz offset from the 455 kHz tone (at 454 and 456).

The limitation seems to be the 8192 points. If I use that then I only get about 18 points per cycle of the 455 kHz using one cycle of the 1 kHz (1 ms). So the step size was 122 ns.

Knowing this can I get a decent waveform? Or, rather, a better waveform than what I'm getting or is the 8192 a limitation for me?

jom
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Re: AM Waveform of AWG

Postby ziko » Fri Aug 06, 2010 11:24 am

Hi discussing this with one of my colleagues, this would not really be possible to do as the amplitude is varying all the time.

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Re: AM Waveform of AWG

Postby jom » Fri Aug 06, 2010 10:02 pm

Hi Ziko

I apologize but I don't know what you mean by the "amplitude varying all of the time". Doesn't a normal sinewave have it's amplitude "vary" all of the time? In fact, don't ALL waveforms have amplitudes that vary all of the time? :?:

I really REALLY need this to work and I don't see how it's really any different that other functions you can build in the AWG.

Maybe you can answer this: What is the purpose of setting the "frequency" in the AWG window after you do an IMPORT? I'm not sure what that refers to? What does it accomplish?

Thanks for any help you can give.

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Re: AM Waveform of AWG

Postby ziko » Mon Aug 09, 2010 3:21 pm

Yes of course the amplitude will change however you cannot do what you are asking for. Creating a frequency of 455KHz is no problem however this will be of fixed amplitude tone, however trying to change the amplitude by 1kHz is not possible to do. The AWG functionality is not meant to replace a signal generator with modulation capability.

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