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Frequency Sweep Question/Harmonic calculations

Question asked by rfdave on Nov 13, 2009
Latest reply on Nov 20, 2009 by rulonv

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Hi All

Another sweep question. I'm designing a transmitter, and I'm sweeping the tx frequency. I'd like to plot the 2nd and 3rd harmonic of the transmitter frequency, with the transmit frequency on the x axis, and the fundamental, 2nd harmonic and 3rd harmonic on the y axis. I can extract the power at the output node, but I don't understand how to extract out the spectral components at a specific frequency. Looking in the data set, I don't really see where the data is stashed.

Thanks
Dave

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SERGEYTRU Nov 13, 2009 9:57 AM
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Hi Dave,
Simplest way for that - add new variables to swept analysis dataset, extracting amplitude of each harmonic, than set checkbox in sweep "Propagate analysis variables ..".
To get N-th harmonic of HB solution spectrum use expression [Freq@Freq[N+1]], so for fundamental of P2 it will be H1=P2[Freq@Freq[2]], for 2nd harmonic it's H2=P2[Freq@Freq[3]], etc.
For additional info see attached wsx.
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- HBsweep.wsx66.1 KB
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rfdave Nov 17, 2009 11:37 AM
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Hi:

Unfortunatly, I'm using Spectrasys, and not the harmonic balance simulator, so my simulation is slightly different. I've taken the X-Band upmultiplier example and modified it to show a similar situation to the simulation I'm building. I'd appreciate any help on this.

Thanks

Dave
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- X Band Up Converter.wsx105.2 KB
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rulonv Nov 18, 2009 5:58 AM
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Take a look at the shipping example:

C:\Program Files\GENESYS200X.XX\Examples\Spectrasys\Paths\Forced Path Frequency.wsx

This shows how to create a path and force the frequency to track a harmonic. What you will want to do is to create a unique path for the 2nd and and 3rd harmonics respectively. I would disable any sweeps until you are able to verify that you have the paths setup up properly and you are getting the anticipated channel frequency and power for all the desired components. At that point re-enable the sweep and then plot the channel powers for each of the paths.
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rfdave Nov 18, 2009 12:57 PM
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Excellent example. Quick question. It seems that in a frequency sweep, I'd want the frequencies in the path to be determined by an equation, not at a fixed value. Just replacing the 7 GHz in the harmonic path with 4*F, where F is defined as 4*1.75 GHz, get's me an error flag. How can I fix that?

Thanks

Dave
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rulonv Nov 18, 2009 1:10 PM
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Just use a vector of variables instead of trying to use math in the field.

i.e. Channel Frequency: Freq1; Freq2; Freq3

Then set the frequency variables to what you want in an equation block. In the equation block it is ok to use the math like 4*1.75 GHz.
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rfdave Nov 18, 2009 2:49 PM
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so I have defined F_TX, F2ndH = F_TX*2, and F3rdH = F_TX * 3, all in an equation sheet attached to the schematic.

Setting the contents of the channel frequency field in the edit path box equal to

IF_FreqMHz; F2ndH; F2ndH

(Copied and pasted from the field)
then I get an error "Syntax error at Line 1 Statement expected.("lnl_i=IF_FreqMHz; F2ndH; F2ndH") "

If I define a vector in the equation sheet

Path2nd = [IF_FreqMHz; F2ndH; F2ndH]

and use that as the contents of the channel frequency field, then I get an error message that the Variable 'Path2nd' on line 1 is not defined.

?

Thanks

Dave
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rulonv Nov 18, 2009 3:02 PM
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Can you attach and example that we can take a look at?
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rfdave Nov 19, 2009 6:12 AM
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I'd be happy to set that up, I'll get that today.
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rfdave Nov 19, 2009 1:45 PM
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Here is a modified version of the Forced Path Frequency that shows the behavior I mentioned earlier
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- Forced Path Frequency.wsx75.0 KB
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rulonv Nov 20, 2009 5:00 AM
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The problem is that the System Analysis can't find the equations because the equations in the schematic are local to the design. The equations need to be moved to an equation block in the workspace tree. The System Analysis can find those equations. I also changed the equation block units.

I have attached an updated file.
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- Modifed Forced Path Frequency.wsx81.3 KB
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rfdave Nov 20, 2009 5:56 AM
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Thanks, I'll take a look at it. I thought that it would be something simple. Do you know where the equation hierarchy and scope are documented?
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rulonv Nov 20, 2009 6:08 AM
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There is some doc in:

Contents > User's Guide > Equations > Hierarchy in Equations

However, it appears this doc is deficient and doesn't address the issues of equations in the design. I will write up a doc enhancement request to address this issue.

Thanks for pointing this out.
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Frequency Sweep Question/Harmonic calculations

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