Frequency Response Analyzer with Bode Plots

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hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer » Sat Nov 16, 2019 3:22 pm

lech226@gmail.com wrote:
Fri Nov 15, 2019 1:52 am
Hi hexamer.
Thanks for your reply.
I mean. for example:
- Input 1Vpp 1khz -> Vacuum tube amplifier -> 8Vpp output with perfect Sine Wave -> Capture
- Input 1Vpp 15khz -> Vacuum tube amplifier -> 8Vpp output with Sine Wave was cut off the head (not perfect Sine wave output) -> Capture

in the both case, 8Vpp Output capture but the second one is Distortion.
Thank you for the clear explanation. I see what you're talking about. Clipping distortion would result in energy being moved to higher order harmonics in the frequency spectrum. So, a frequency response would only show you is that the gain is limited. As long as the FRA sampling rate is high enough to avoid aliasing-in these higher order harmonics, then they won't show up in the frequency response. This sampling rate can be increased in the settings, but the default is 64x the stimulus frequency.

The only way that the Bode plot would indicate that some distortion may be occuring would be for you to compare the FRA plotted gain to what you think amplifier is set to (within the bandwidth of the tube). For instance, if your amplifier is set to amplify by 10x, and the gain response is lower than 20 dB, then there may be clipping distortion. There are diagnostic tools built into the FRA application that can measure purity of the input and output signals if you wanted an objective number of clipping distortion. But for a first pass to see if there is any distortion, you'd probably be better off using the PicoScope oscilloscope application.

lech226@gmail.com
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Re: Frequency Response Analyzer with Bode Plots

Post by lech226@gmail.com » Mon Nov 18, 2019 1:49 am

Hi Hexamer.
Have a nice day.'Thank you very much for your clear description
I got it.That's is very mean to me.
I would to buy one for my purpose.
Thank you.

igorfier
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Re: Frequency Response Analyzer with Bode Plots

Post by igorfier » Wed Dec 18, 2019 7:28 pm

Dear Aaron,

I just stumbled upon your very nice application while looking for ways to implement FRA functionality to my 2204A. It installed just fine in W10 x64 and initialized my scope upon startup.
I am now trying to measure simple circuits such as a resistor and capacitor in parallel, but I can't get any meaningful data. I suspect I didn't quite get the way the leads should be connected.
Here's what I'm doing, based on the posts I found about the same subject:

- At one end of the RC: inner bayonet of the CH-A BNC and inner bayonet of the AWG;
- At the other end of the RC: inner bayonet of the CH-B BNC and outer shield of the AWG.
- The outer shields of the CH-A and CH-B BNCs are left floating.

What am I doing wrong?
Thanks in advance for your answer and your time.

Best regards,
Igor Fier

kaimex
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Re: Frequency Response Analyzer with Bode Plots

Post by kaimex » Wed Dec 25, 2019 2:15 pm

Hi Igor,

with Channel B input connected to the shield of the AWG you are shorting that input to ground.
The shields are all connected.
With channel A connected to the AWG output and your RC-circuit connected between the A and B inputs you get a voltage on input A that is Z_RC/(Z_RC+RoutAWG)*UoutAWG.
I have forgotten the exact Rout, guess it was somewhere around 600...700 Ohm.
When your RC-circuit has a very high impedance compared to that, you will get almost the full AWG output voltage. If Z_RC is very small compared to RoutAWG, you will get almost nothing.
You will get something meaningful, if Z_RC is not to far away from Z_out.
If Z_RC is very high, you have also to consider the input impedance of channels A & B of ~ 1 MOhm.

Regards Kai

STMN
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Re: Frequency Response Analyzer with Bode Plots

Post by STMN » Tue Jan 28, 2020 12:12 pm

Hello,

many thanks for that usefull tool, is that possible to change X axis to linear view? I intend to measure the frequency response of a IF filter, please see the attached file here:
https://www.picotech.com/support/topic40059.html?&p=143399#p143399

Best Regards

hochfrequenz
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Re: Frequency Response Analyzer with Bode Plots

Post by hochfrequenz » Sun Feb 02, 2020 6:36 pm

Hi there,
would like to install the FRA Bode-plot- program. The instructions in the wiki are out of date. Can someone explain what I have to do. I'm really overwhelmed. I have attached a screenshot of the download page.

WIN 10 64bit, Picoscope 2205A

Marco Schramm
Attachments
Picoscope  FRA  WIKI  downloads.jpg

ts8051
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Re: Frequency Response Analyzer with Bode Plots

Post by ts8051 » Wed Feb 12, 2020 7:14 pm

Hello, I downloaded your application for pico 3000 oscilloscope fra4picoscope and it is working properly in my MAC under VMware. Please let me know if there is a possibility to compile it for use in MAC OS. I live in Athens, Greece

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer » Sat Feb 15, 2020 9:47 pm

STMN wrote:
Tue Jan 28, 2020 12:12 pm
Hello,

many thanks for that usefull tool, is that possible to change X axis to linear view? I intend to measure the frequency response of a IF filter, please see the attached file here:
https://www.picotech.com/support/topic40059.html?&p=143399#p143399

Best Regards
If you strictly wanted to plot in linear view, you could export the data and re-plot it. But I assume you probably actually want to have the frequency samples in linear mode too. Unfortunately the application isn't currently designed for that use case, but I do have plans to do that some day.

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer » Sat Feb 15, 2020 10:08 pm

hochfrequenz wrote:
Sun Feb 02, 2020 6:36 pm
Hi there,
would like to install the FRA Bode-plot- program. The instructions in the wiki are out of date. Can someone explain what I have to do. I'm really overwhelmed. I have attached a screenshot of the download page.

WIN 10 64bit, Picoscope 2205A

Marco Schramm
Hi Marco,

First, you should download and install the latest version of the 32 bit Pico SDK: https://www.picotech.com/download/software/sr/PicoSDK_32_10.6.13.97.exe

Then you should be able to download and install the latest version of the FRA app from the downloads page. Here's a direct link: https://bitbucket.org/hexamer/fra4picoscope/downloads/FRA4PicoScope%200.6.2b.msi

Let me know if you run into issues.

Thanks,

Aaron.

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer » Sat Feb 15, 2020 10:14 pm

ts8051 wrote:
Wed Feb 12, 2020 7:14 pm
Hello, I downloaded your application for pico 3000 oscilloscope fra4picoscope and it is working properly in my MAC under VMware. Please let me know if there is a possibility to compile it for use in MAC OS. I live in Athens, Greece
The UI portions of the FRA application are very Win32 API specific. Even the "backend" software is probably not perfectly portable. So, to make it portable and compile it all for MAC would be a really big undertaking.

I'm glad to hear you can run it in a VM. I've had pretty good success with that approach too as it's the only realistic way I can still test for Windows XP compatibility.

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