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 Post subject: Bode Plotting, Frequency Response Analysis (FRA), Labview
PostPosted: Jun Wed 12, 2019 3:02 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 189
Location: Suburban Chicago
Hi all,

The background is that I am thinking about upgrading an old but quite capable PicoScope USB Oscilloscope with a stand alone digital oscilloscope from Rigol or Siglent or ??? Sometimes it's just nice to have a standalone instrument even though the Picoscope can do a lot.

After looking for a while I noticed that some of the latest scopes can do Bode plotting which you may prefer to call frequency response analysis (FRA) or something similar. One model from Keysight, the EDUX1002G (on sale for $570 at TestEquity.com right now, June 2019) uses a built in signal generator to generate the plots. Others like the Siglent SDS1102X-E are able to control external generators. Of course that results in a higher cost the Siglent plus, say, a SDG830 comes in at $770 before any discount codes or sale prices. But both the Siglent scope and generator are more capable than the Keysight option so either choice could be a good one and when the sale ends the Keysight is priced at $670.

But another option is to use a PC to control a scope and generator using Labview Home (or something similiar?) which is only $50. This would decouple the scope and generator choices from the very short list of models that have the native capability to do Bode plotting. It does violate my stand-alone goal but in the case of a more sophisticated task like Bode plotting I consider that acceptable. The advantage of using scopes and generators that are known to work together to do this job is that they are known to work together. Controlling scopes and generators from Labview would depend on the availability of suitable Labview drivers for the gear you want to control and I don't know if it is always possible to assess that in advance. I don't see any drivers on the LabView site for Rigol or Siglent products but both of those companies are fairly good about posting programming guides for their products and they typically mention LabView among other programming options so I think that I would be able to build a system I could control from my PC. And that opens the door to automated measurements of many kinds, not just Bode plotting.

I realize that this is way beyond what most of you want or need to do but surely some others here are interested in the ability to sweep IFs for example or design new gear as well as restore old radios. If anyone has any thoughts or experiences with this sort of thing I would love to hear them. For the last few days I have been all gung ho on getting a scope with native Bode plotting capability but now I am starting to lean towards using a PC to do this kind of work.


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 Post subject: Re: Bode Plotting, Frequency Response Analysis (FRA), Labvie
PostPosted: Jun Wed 12, 2019 5:31 pm 
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Joined: Aug Sat 02, 2014 3:59 am
Posts: 1166
Location: Brooklyn, NY 11217
I use the Analog Discovery from Digilent to do this. I bought it for $200 through my wife's school They are $279 street price. Not sure it would work for you, but it is a scope and sig generator etc.


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 Post subject: Re: Bode Plotting, Frequency Response Analysis (FRA), Labvie
PostPosted: Jun Wed 12, 2019 6:13 pm 
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Location: Sanford Fla 32771
I use a Siglent signal generator for sweep (Model 1025). It is easy to setup for sweep, you set start freq and stop freq and sweep time. It provides a sync signal for the scope. My justification was the sig generator can be used for other projects requiring pulse, sine, ramp, noise, square wave, all up to 25mhz.
Below is a 455 khz if xformer sweep. This was with linear sweep, but logarithmic is also available.
The text on the o'scope screen was edited by me, but the square wave from the Siglent shows the start stop freq markers. The 2nd shot shows the Siglent setup screen.


Attachments:
1st_IF.JPG
1st_IF.JPG [ 94.88 KiB | Viewed 207 times ]
1st_IF_SETUP.JPG
1st_IF_SETUP.JPG [ 230.93 KiB | Viewed 203 times ]

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 Post subject: Re: Bode Plotting, Frequency Response Analysis (FRA), Labvie
PostPosted: Jun Thu 13, 2019 5:23 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 189
Location: Suburban Chicago
Thanks for the responses.

Analog Discovery module:

What a neat little tool! Yeah, I can see that it does a lot of things that would be useful and has a frequency range that is suitable for AM radio work along with at least some shortwave radio work. In my case it duplicates (but also updates) what I can do with my PicoScope and I am looking for a standalone DSO right now so I will pass. But I will keep it in mind for the future and it is certainly worth a look for those who are just starting out.

Siglent generator:

At the moment I have a cheap generator that can probably do the same thing just as well with a little work. And it should be possible to use the scope's FFT mode in peak hold mode and use any generator that can sweep slowly through the desired range. I believe I have done that a time or two with the PicoScope. I am currently leaning towards the 2 channel Siglent SDS1202X-E which has a 200 MHz BW which is nice for RF work and an excellent FFT function at a price more attractive than its 4 channel siblings. I am making a probably futile effort to talk Siglent into adding the Bode function and the FFT marker functions to the 2 channel firmware. Both would make it much more attractive to 2 channel RF customers like me and as I told them it would result in my buying one of their generators too, rather than using what I already have....

So we will see how that goes but I am not holding my breath. If I were to get a generator the SDG1025 is one of the ones on my short list.


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