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Tullos
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| Oscilloscope software for a computer |
 Posted: Tue Nov 30, 2004 3:04 pm |
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has anyone used any good free software that has this function? It seems cheaper than buying a scope. Input wanted.
Thanks
Tullos |
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Haplo
Joined: 06 Sep 2003
Posts: 659
Location: Sydney, Australia
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| Posted: Tue Nov 30, 2004 6:24 pm |
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| There is no such thing as a 'free oscilloscope' software. Remember software oscilloscopes still need some custom hardware attached to your PC (the data acquisition modules and the probes). So even if you find a software for free you will still have to pay for the hardware. |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Tue Nov 30, 2004 8:14 pm |
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Not free but a truly versatile tool. Check out www.bitscope.com they have a "pocket" DSO with logic analyser and waveform generator.
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Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Guest
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| Posted: Wed Dec 01, 2004 2:12 pm |
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| asmallri wrote: | | Not free but a truly versatile tool. Check out www.bitscope.com they have a "pocket" DSO with logic analyser and waveform generator. |
Not so sure about this one...... 100MHz analog with only 25MS/S ! Something wrong ! |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Wed Dec 01, 2004 6:55 pm |
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I do not know where the 100MHz is derived but you have to have a higher frequency response on the analog front end than the sampling rate otherwise you end up modifying (filtering) the waveform you are sampling. For example, if you had a frontend bandwidth of 25MHz that means the output of the analog stage will will 3dB lower than the input voltage at 25MHz - obvioulsy not what you want.
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Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Wed Dec 01, 2004 7:03 pm |
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| Quote: | | Input bandwidth refers to the analog input circuitry and compensated A/D convertor. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Thu Dec 02, 2004 8:13 am |
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| Anonymous wrote: |
Not so sure about this one...... 100MHz analog with only 25MS/S ! Something wrong ! |
If the analog bandwidth is greater than Nyquist for the sampling rate you will get aliasing which will drive you mad in a piece of test gear. High frequency garbage you can ignore will be frequency folded into low frequency artifacts. You may spend days battling problems that don't exist!
I surely hope they have an anit-aliasing filter that can be switched in. Otherwise I would steer very clear of this.
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The search for better is endless. Instead simply find very good and get the job done.
Last edited by SherpaDoug on Thu Dec 02, 2004 3:41 pm; edited 1 time in total |
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newguy
Joined: 24 Jun 2004
Posts: 1903
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| Posted: Thu Dec 02, 2004 11:57 am |
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Keep in mind that the scope may be using some sort of "sample dithering" to achieve the 100 MHz bandwidth with only a 25 MS/s digitizer through repetitive sampling.
HP made an oscilloscope (can't remember the model #) that had a 1 GHz bandwidth, yet the digitizer only ran at 40 MS/s. It achieved the high bandwidth by sampling for a set time, then introducing a time shift to the sample clock, resampling to "fill in the gaps" between the 1st set of samples, etc. The only downside is that a scope of this nature can't be used to capture fast glitches (i.e. single shot mode) - only fast repetitive waveforms. |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Thu Dec 02, 2004 2:37 pm |
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| newguy wrote: | Keep in mind that the scope may be using some sort of "sample dithering" to achieve the 100 MHz bandwidth with only a 25 MS/s digitizer through repetitive sampling.
HP made an oscilloscope (can't remember the model #) that had a 1 GHz bandwidth, yet the digitizer only ran at 40 MS/s. It achieved the high bandwidth by sampling for a set time, then introducing a time shift to the sample clock, resampling to "fill in the gaps" between the 1st set of samples, etc. The only downside is that a scope of this nature can't be used to capture fast glitches (i.e. single shot mode) - only fast repetitive waveforms. |
Repetitive sampling schemes (sequential and random) have been around since the dark ages of oscilloscopes. Tek and HP have and still do make (HP=Agilent now) scopes that use repetitive sampling schemes. The key to using them properly is knowing when the scope switches over (or if it switches at all) from a single-shot sampling method to a repetitive method. Often times it is not explicitly stated on the instrument, only found on in the manual or by careful inspection of the waveform on the screen.
In fact, it is VERY important to know when and under what conditions a digital oscilloscope will "lie" to you. 
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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Kenny
Joined: 07 Sep 2003
Posts: 173
Location: Australia
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| Posted: Thu Dec 02, 2004 4:02 pm |
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| Yes, with digital-only scopes, aliasing can catch you out. That is why I have always liked the Hameg scopes - with one button press they become analog scopes so you can really see what's going on with repetitive waveforms. They are also very good value for money. |
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