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Old 17th March 2008, 01:45 PM   #1
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Default lower cost options for spectrum analyser/ function generator?

Hey
Is anyone using software based spectrum analysers/ function generators? I have had a look on ebay for these items and they are obviously pricey.
What basic features would one find desireable in each type of equipment
Has anyone out there used software based ones and is so are they any good
Many thanks
Nick
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Old 17th March 2008, 02:04 PM   #2
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Save your cash!

For audio work a PC is all you need, and some freeware.

I like e-Cat's function generator:

http://e-cat.nm.ru/sinegen/

use the "white noise" function to test frequency response, or individual tones for specific testing

feed the output (line level) into your sound card & see the spectrum with this FFT analyser from Japan:

http://www.ne.jp/asahi/fa/efu/soft/ws/ws.html

A sound card that can sample 96Ks/s at 24bit is good enough for much work, 192/24 is riding first class!

All these survived an Ad-Aware check after loading!
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Old 17th March 2008, 02:37 PM   #3
kevinkr is offline kevinkr  United States
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I use audiotester from www.audiotester.de Quite popular around here and the latest version is really good.

The results will only be as good as your sound card, and it really helps to use something that runs the Via Envy 24 chipset or similar so that you are not limited to 48kHz sample rates. I use M-Audio Transit with my laptop which is limited to 24 bit/48kHz in duplex mode on USB, (USB limitation I believe) and an M-Audio 2496 in the media server which can run at 96K.

I designed and built an interface some years ago to protect the snd card inputs, provide additional attenuation for higher voltage measurements like power amplifiers (0dB, -20dB, -40dB, -60dB), input impedance is 100K, and I have also provided gain on the generator outputs (0dB, +6dB, +12dB) The inputs to the sound card have active clamps that also light overload leds for visual indication that the signal levels are too high - on FFTs this is quite visible anyway, but it is useful to know what is getting overloaded. Operation is via a pair of 9V batteries for low noise with simplicity. The SFDR of this setup with the transit is better than 90dB and the noise floor is somewhat below -100dBv, so it's quite useful in fact. (Not close to the theoretical limits for 24 bits though.) My last hardware based analyzer (a Singer) was hard pressed to produce a SFDR of 60dB.
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Old 17th March 2008, 04:41 PM   #4
Gordy is offline Gordy  United Kingdom
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ARTA looks promising:
http://www.fesb.hr/~mateljan/arta/index.htm
...and not so expensive.
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Old 17th March 2008, 05:05 PM   #5
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Gordy
ARTA looks promising:
http://www.fesb.hr/~mateljan/arta/index.htm
...and not so expensive.

Not sure what your definition of "not so expensive" actually means, but at $255 (USD) to unlock and license Arta software, versus about $55 (USD) for audiotester it's no bargain. I can think of a whole lot of other things I would rather do with that kind of money..

Arta will not allow you to save files, set ups or anything else in demo mode. It is seriously good measurement software for room measurements and speaker design. For testing electronics it is total overkill.

Unless you need the additional sophistication of Arta (which I have tried and like) Audiotester will get the job done well and is much less expensive. The latest version is very good, easy to use, and set up.
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Old 17th March 2008, 05:06 PM   #6
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Really nice inexpensive gear over here....
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Old 17th March 2008, 06:31 PM   #7
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Quote:
Originally posted by kevinkr

I designed and built an interface some years ago to protect the snd card inputs, provide additional attenuation for higher voltage measurements like power amplifiers (0dB, -20dB, -40dB, -60dB), input impedance is 100K, and I have also provided gain on the generator outputs (0dB, +6dB, +12dB) The inputs to the sound card have active clamps that also light overload leds for visual indication that the signal levels are too high - on FFTs this is quite visible anyway, but it is useful to know what is getting overloaded. Operation is via a pair of 9V batteries for low noise with simplicity. The SFDR of this setup with the transit is better than 90dB and the noise floor is somewhat below -100dBv, so it's quite useful in fact. (Not close to the theoretical limits for 24 bits though.) My last hardware based analyzer (a Singer) was hard pressed to produce a SFDR of 60dB.
Kevin,

Do you mind sharing the schematic for this interface?

TIA,

-- josť k.
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Old 17th March 2008, 06:33 PM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by korneluk


Kevin,

Do you mind sharing the schematic for this interface?

TIA,

-- josť k.
I'll look and see if I have the original, it's been quite a while since I built it, and IIRC I never made anything more than an informal schematic.
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Old 17th March 2008, 06:57 PM   #9
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If you are happy to install and run Linux, look at baudline, which is without charge, but not Open Source.

See http://www.baudline.com/
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Old 17th March 2008, 07:17 PM   #10
KSTR is offline KSTR  Germany
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Kevin, no need to buy ARTA. Website reads The demo mode of programs is fully functional except loading and saving of files. To "save" a measurement you still can use a plain screen hardcopy. Older versions exist that aren't protected and are fully functional.

LTSpice (a *free* circuit simulation software) also has FFT capapilities, plus a .WAV interface (read and write). It can be used to create and analyse test signals, which may be not as convenient (not real time mode, etc, and you need to put some time and effort into it) as a true generator/analyser, but it's possibilities are not limited in any way -- and it's free.

- Klaus
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