PC as scope and spectrum analyzer?

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Hi folks,
I want to get back into electronics,breadboarding and solderslinging,the works.It has been awhile.I have a couple of meters.I know I need a scope.It seems like the last time I picked up Electronics World there is a way to use one's PC as a scope,spectrum analyzer,etc. with the proper software.Is that right?That is fabulous if so.Save me from having to invest in a scope,not that they are that expensive,especially on the used market.Nonetheless one can save space at the very least with a scope PC.Any info on this subject,pro or con,would be greatly appreciated.Thanks tons in advance.
Joined 2001
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AudioXpress magazine (formerly Audio Amateur, then Audio Electronics) published a series of reviews a few years ago by Charles Hansen of different PC-based instruments. I found it to be a good source of information when I was looking. The magazine is at http://www.audioxpress.com if you're interested.

As you may already know, choosing one of these units involves a three-way tradeoff between bandwidth, resolution, and cost. (The software interface is also a factor, but probably not until you've settled on the first three.) Most of the affordable units I've seen have 8-bit resolution, which gives you about 54 dB noise floor as a spectrum analyzer -- somewhat limiting for audio work, I think. I'd suggest going for at least 12 bits (= 80 dB noise floor) if you can afford it.

For bandwidth, I'd go as high as the wallet will allow, especially if you are designing feedback amplifiers and want to see those HF oscillations. 20 MHz is probably a minimum figure, but you could be forgiven for wanting anything up to 200 MHz in my view.

What will this cost? I haven't surveyed the field recently, but I do know of a model by Pico Technologies (http://www.pico-tech.co.uk) that offers 12-bit resolution and 25 MHz bandwidth for about $750 US. They also have a 50 MHz model for just over a grand. I have a different Pico model and am happy with it, but am not otherwise affiliated with the company.
I understood what you meant is software to be used with a soundcard as the interface... yes, such software exists (try a few searches on www.download.com). Of course, you're limited with bandwidth, resolution and SPECIALLY, on the voltage the input can take (most scopes are virtually undestructibles in that sense), but, free (or almost) is the best price :) Hope that helps!
cheap PC scope and analyzer

There are a number of software packages on the Web for using a PC as a scope or THD/Spectrum Analyzer. I have been using the following software which has a free demo and is cheap to purchase, $35 I think. www.sumuller.de/audiotester/
Can get around 80 dB dynamic range with most sound cards I think. I am now using a 24 bit 96KHz sampling card made by M-Audio, Audiophile 2496, street price around $160 (check zZounds.com) which gives around 100 db range. (.002% distortion) For THD analysis can add this circuitry to measure down to typically .0001% distortion: http://www.angelfire.com/ab3/mjramp...d/golopid6.html

There are quite a number of software programs available that will measure distortion and generate test signals. These all use computer sound cards. With the right sound cards you can generate test signals with very low distortion (.0002%) or better and measure distortion down to around -130DB with little problem in the analog mode. They also let you test for jitter and so forth.

What you can do with this software depends to a large degree on the quality of your sound card. You can expect to pay $400 on up to $800 or so for a suitable one. The newer 24 bit cards with samplig rates to or exceeding the 96KBs sampling rate are preferend. A sound baster card will not do and the built in sound cards on mother boards have to much noise to be useable below about -80DB.

Two such software programs that I use are HPworks and a version of SpectraLab that Pioneer Hill software sells. SpectraPro is also a good choice. HPworks is harder to use but may be more accurate. With a 16 bit 44.1 Kbs sound card you will be limited to a upper frequency of about 22 Khz. Thus you cannot measure third harmonic distortion past the 7 Khz fundamental frequency with that sampling rate. So additional test equipment is normally always required.

I would not consider using a sound card for a scope because the performance would be very poor and to limited in frequency response.

There is no need to build distortion analyzers or most other test equipment since suitable equipment can be purchased on Ebay for very reasonable prices. I have sold quite a number of my older equipment items there.

Vintage HP distortion analyzers such as the HP 334 sell for as little at $85.00 older versions such as a 331 sell for around $35.00. You will likely find all the test equipment you need available on Ebay. Look at the industrial section and then test equipment.

John Fassotte
Alaskan Audio
Has anyone considered <a href="http://www.bitscope.com/design/">The Bitscope</a>, an open design 100MHz Digital Sampling Oscilloscope and 8 channel Logic Analyzer.

<li>Simultaneous analog/digital capture
<li>100 MHz sub-sampling bandwidth
<li>50 Ms/s logic sample rate (max)
<li>40 Ms/s analog sample rate (max)
<li>20 MHz single-shot bandwidth
<li>4 analog inputs (multiplexed)
<li>8 logic inputs via DB25 POD
<li>Two 32K x 8 capture buffers
<li>Sophisticated triggers (analog or digital)
<li>1GHz Prescaler/frequency counter

The Complete Kit. US$290.00 or you can just get the pcb/chipset and try to source the rest youself


I don't recommend using soundcards for a "pc-scope". The input of soundcards is often DC-protected, so you can't measure DC-signals; the inputvoltage is often limited to +0.6V and -0.6V (with two simple diodes) and as mentioned above the bandwith is also limited.

Best regards,

The whole thread should maybe reside in the "everything else" forum, but never mind.

With regard to building a high resolution distortion/spectrum analyzer, an external TI PCM1802 would make an excellent convertor, question is how to get the sdata at 6 MHz+ inside the computer.

Anybody know a sound-card or other add-on that has a 24 bit/96 or 192 kHz SPDIF input?

Or any other idea how to get three separate data lines (bitclock, sdata, LRclock) into the computer? There used to be AT-slot digital I/O cards and there are some more expensive PCI I/O cards now, but none will tell what that max data rate is.

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