Any high resolution diy spectrum analyzers ? - diyAudio
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Old 5th March 2012, 03:24 AM   #1
percy is offline percy  United States
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Default Any high resolution diy spectrum analyzers ?

With many 24bit/192Khz soundcards and audio interfaces on the market these days and lots of freeware programs you dont even need to do anything special for signal analysis upto that frequency and dynamic range resolution. What I am curious is why arn't there any (or atleast I haven't managed to find any) pc based diy spectrum analyzers, especially the hardware, for higher sampling rates. I see that there are a few 16+ bit (enob) ADC chips from TI and AD that have sample rates of several (2-10) MSPS. I mean if anyone can build a 12bit 1MSPS "pc scope" then why not a 24bit 4MSPS spectrum analyzer ? What difficulty could be preventing this from happening ?
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Old 5th March 2012, 05:10 AM   #2
gootee is offline gootee  United States
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If you google for "build spectrum analyzer" you will find many:

Google

But a lot of them are analog and meant for RF (Radio Frequency) work. But even some of those would be nice to have, if they go down to around DC, as some do.

Below are a few links, but not necessarily the best ones, since I didn't look at most of the search results.

Our big Aeroflex analyzers at work are based on digital sampling and playback hardware (512 MHz recorded bandwidth that you can put anywhere from 0-6 GHz!), with everything else done in software. It seems like all you would need would be an off-the-shelf data acquisition module and some software, especially if the display didn't need to be "real time". I'd guess there's got to be some already-done stuff out there, like that. 50 to 100 MHz should be plenty high-enough for most audio work, although 200 MHz would be nicer. Anyway, there are some below that go to 1 GHz and higher.

Or find a working HP 141T system for around $200 which will get you to 110 MHz with the lowest frequency plug-in. Even a cheap non worker is easy to fix as long as the CRT is OK.

A Network Analyzer and Bode Plotter sure would be nice to have, too.

Spectrum Lab by dxzone.com

Build a 1000 MHz RF Spectrum Analyzer Inexpensively

http://www.signalhound.com/

BITSCOPE = PC OSCILLOSCOPES AND ANALYZERS (link to construction article at bottom)

Homebrew spectrum analyser

http://www.google.com/url?sa=t&rct=j...OIFk0Huy0uy8CQ

Create a FFT Analyzer part I: prerequisites, concerns and setup Sample & Hold

Lots of SA links:

Spectrum Analyzer - Technical Reference: Spectrum Analyzers

Google search for "spectrum analyzer ADC OR sampling OR "data acqisition"":

http://www.google.com/#hl=en&gs_nf=1...w=1280&bih=818

Last edited by gootee; 5th March 2012 at 05:25 AM.
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Old 5th March 2012, 07:06 AM   #3
gootee is offline gootee  United States
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Virtins Technology: Turn a PC into Virtual Instrument - Products Analyzer

2x100MHz PC USB Oscilloscope, Spectrum Analyzer, Multimeter, Signal Generator*

Last edited by gootee; 5th March 2012 at 07:25 AM.
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Old 5th March 2012, 04:32 PM   #4
percy is offline percy  United States
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The words "high resolution" in the subject were intentional. By high resolution I meant anything over true (enob) 16 bits, as I would imagine to correctly analyze a 16bit(audio) signal the analyzer would have to be more than 16bits.
Can you tell me if any of these spectrum analyzers have more than 16bit (-96db) resolution AND more than atleast 2Mhz spectrum range ? Imagine if you'd like to investigate -80db 500khz smps noise/ripple riding on the signal, or if you'd like to investiage amp oscillation into a few Mhz range. How would you be able to do that with a spectrum analyzer that has 12 or 8 bit resolution ?

Last edited by percy; 5th March 2012 at 04:39 PM.
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Old 5th March 2012, 06:31 PM   #5
benb is offline benb  United States
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It seems like it would be a small market, as someone famous might have said, "24/192 should be more than anyone could ever need for audio."

Since the A/D chips are available, it would just be a matter of making the interface with enough buffering, bandwidth, the latest USB or other high-speed interface, etc. I smell a raspberry pie here.

A near-off-the-shelf solution would be to use a standard interface for the audio band, and also send the signal through a high-pass filter set around 20kHz to 100kHz with that going to a 12 to 16 bit interface that goes up to several MHz. The filter would get rid of most of the "large" audio-band signals, and you could crank up the gain to get better resolution. Of course if an amplifier is oscillating rail-to-rail at 1MHz, you'd want the option of full attenuation on the the higher band as well.

And it would only take a "simple matter of programming" for the PC to read both of these interfaces and put the composite signal on one spectrum display.
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Old 5th March 2012, 07:04 PM   #6
von Ah is offline von Ah  United States
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Default 640k is all anyone will ever need

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Old 6th March 2012, 02:56 AM   #7
gootee is offline gootee  United States
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Quote:
Originally Posted by percy View Post
The words "high resolution" in the subject were intentional. By high resolution I meant anything over true (enob) 16 bits, as I would imagine to correctly analyze a 16bit(audio) signal the analyzer would have to be more than 16bits.
Can you tell me if any of these spectrum analyzers have more than 16bit (-96db) resolution AND more than atleast 2Mhz spectrum range ? Imagine if you'd like to investigate -80db 500khz smps noise/ripple riding on the signal, or if you'd like to investiage amp oscillation into a few Mhz range. How would you be able to do that with a spectrum analyzer that has 12 or 8 bit resolution ?
I already gave you sufficient links. Even a 10-minute perusal tells us that yes, many of them do _WAY_ better than -96 dB, and yes, many of them do from DC to several GHz.

This type of stuff just isn't that hard, any more. I saw one PDF for a single college undergrad Lab course session where the students were supposed to do all of that and more during just one week of the lab course, having designed and implemented the RTOS (real-time operating system) for their embedded processor in the two prior weeks!

And if you look at the links for some of the many that are labeled as "sound card" spectrum analyzers, you will see that many or maybe most of them can instead use other ADC data acquisition hardware, which is most-definitely not restricted to audio-type sample rates or word sizes.

So maybe you should go look at the range of data acquisition/sampling/ADC (analog to digital converter) solutions that are out there. THAT is what might limit the specs. But we already know that 1 Hz to multi-GHz and -150 dB are pretty easy and are available ready-to-use, with software, for under $1000, with possibly-lesser capabilities (but still FAR above audio-type sampling) available for much less.

I guess it will come down to how much you want to spend and/or how much DIYing you are able or willing to do.
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Old 6th March 2012, 03:28 AM   #8
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If it's DIY you want, consider getting one of the Texas Instruments development boards and outboard the signal conditioning/protection and amplification front end -- you can do the programming yourself or use that which comes with them -- I think that TI is one company which likes struttin' their stuff. It isn't always necessary to re-invent the wheel.
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Old 6th March 2012, 04:33 AM   #9
Frex is offline Frex  France
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Hello percy,

To follow jackinj, you can show this ADC from TI.
It's a 24bits 4Msps ADC (it's the faster 24bits ADC i know).
You can purchase the eval board of this IC from TI, that include a software allowing
to perform FFT,THD measurement and much more.

As you, i'm very interested to get high resolution system with better bandwidth than traditional sound card.
Regards.

Frex

You can also read this web site,
It's a very interesting project of 12bits 100MHz acquisition system.
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Old 6th March 2012, 11:00 AM   #10
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Yes, I have an ADS1675EVM. If you purchase one, it's helpful to have some TNC connectors around. Documentation for the EVM's is very good, but you have to read the info about jumpers carefully. Often the EVM's are evaluated and then someone sells them on EBay.
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