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Old 30th November 2004, 06:44 PM   #1
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Default Cheap Spectrum Analyzers

I am have been wanting to purchase a used spectrum analyzer for some time now. I have been looking at the HP3580A for general purpose use.

My only real use for such a thing would be to study noise in amplifiers etc. to be able to see the spectra of the noise and how wire routing etc effects the noise level.

I cant afford a Audio Precision system, maybe a first generation if it was cheap enough.

The HP3580A are on ebay all the time for about 200-250 bucks. But that seems high to me as i used to see them at the swap meets for 100-150

the HP3582 and 3585 jump up to 1000 or so. and a used 1 gen AP is about 800 i think. I cant really afford to spend a grand on something.

what are your thoughts on the 3580A VS????
Anybody in the US have a 3580 they would sell me for $150.00 or maybe take a partial trade etc for???


Zero

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Old 30th November 2004, 06:49 PM   #2
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Sound card and RightMark Audio Analyzer software. It's a free download
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Old 30th November 2004, 06:57 PM   #3
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yes i considered such an option and i do own the SMAART software and have used it as such, but its not calibrated and the soundcards input is limited to what 1 volt?
I would then have to build and add some sort of external attenuator etc and in the end the PC's sound card could add more noise then the source im trying to look at.

a good PC sound card would cost around $100.00 + add the cost of a used PC and Monitor and im at the cost of a 3580....


and then there is the issue of the amount of room a pc would take up, where to put the keyboard and the mouse and the monitor etc...

I would prefer an all in one system if possible. but thanks for the suggestion.


Zero
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Old 30th November 2004, 06:59 PM   #4
tiroth is offline tiroth  United States
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Yes, I have been through this, and the only reason I would get a "real" spectrum analyzer is the bandwidth. The cheap units don't have any more than a soundcard, so why bother?

The better DSOs with built in FFT, jittertrack, etc keep nudging down in price. Hopefully someday soon we can have our cake and eat it too.
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Old 30th November 2004, 07:01 PM   #5
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See what kinda deal you can haggle with Peter at ABC. Normally he thinks his equipment is gold plated but sometimes ya get lucky...

You still looking for PCB trace info?
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Old 2nd December 2004, 06:59 AM   #6
1audio is online now 1audio  United States
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Default Spectrum Analyzer

A swept spectrum analyzer can be very good for looking at some signals, as long as they are consistant, either CW or noise. I have two Tek 7L5's which are very good and convienent if you have a 7000 mainframe. And the 10 Hz to 5 MHz is more than enough for most audio needs. However for measuring low level noise I have found that a good sound card (for me the M Audio Transit usb card) has been more useable. If you get good FFT software w/ high sample counts the noise can be very low allowing visibility of hidden artifacts. The only software I have that can do this is Praxis. But someone must have a free or cheap good FFT package. (I have not found it yet.)

A low noise preamp isn't necessary with most of these since the mike preamp in them is pretty good. A really low noise preamp will require a transformer and other difficult, expensive parts to be signficantly better than a good low noise op-amp.

The M Audio Transit can be had for as little as $75 on line.
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Old 2nd December 2004, 12:09 PM   #7
SY is offline SY  United States
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Fwiw, I used an Audigy 2ZS soundcard with both Rightmark and Dazyweb spectrum analyzer software. The max signal level before distortion began to rise was about 3.5V peak (7V p-p). For attenuation, I just used a 10x scope probe and BUF03-based buffer. The results were so good I didn't believe them until I tested some know sources (like the sine wave source from an HP 3581A) and got correct results. As a practical matter, I'm measuring reliably and repeatably to better than -100 dB below signal reference.
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Old 2nd December 2004, 02:27 PM   #8
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Default Re: Spectrum Analyzer

Quote:
Originally posted by 1audio
I have two Tek 7L5's which are very good and convienent if you have a 7000 mainframe. And the 10 Hz to 5 MHz is more than enough for most audio needs. However for measuring low level noise I have found that a good sound card (for me the M Audio Transit usb card) has been more useable. If you get good FFT software w/ high sample counts the noise can be very low allowing visibility of hidden artifacts. The only software I have that can do this is Praxis. But someone must have a free or cheap good FFT package. (I have not found it yet.)

I have used a TEK 5L4 -- fits into the 5000 series mainframes -- a true "boat anchor" series of scopes but very inexpensive.

I remain a fan of the Hewlett Packard 3581 "Wave Analyzer" -- which has a built in sweep generator and 90dB of dynamic range -- if you null the center frequency with a passive filter you can make very good and acurate distortion measurements. The 3581 is good from 100V down to 100 nanovolt measurement (140dBV/dBM) and can be battery operated. If you have an outboard sweep generator the range of the unit is practically DC to 1.5MHz -- try that with a computer-based card. Usually the 3581 goes for around $50.

I do have a PIC16F84 based "reader" which takes the pen-plotter output and downloads to Excel via RS232 if anyone is interested. Any instrument which outputs 0-5VDC on the horizontal and vertical axes can use the reader. It does require the Win2K version of Excel, however.
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Old 3rd December 2004, 06:56 AM   #9
1audio is online now 1audio  United States
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Can you supply more info or possibly the details for your PIC to Excel solution? I would like to use it with a network analyzer I have consisting of a KH sweep/function generator and an HP gain/phase meter.
-Demian
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Old 3rd December 2004, 10:11 AM   #10
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Default DIY Spectrum analyzer.

Hi,

I have seen some DIY spectrum analyzers which radio amateurs have been doing.
They are of course very complex and hard things to build.

But has anyone here seen schematics for an "audio" spectrum analyzer ? In the range 0hz - 100khz ?

Just wondering, it could be a fun project

Any links or info appreciated

Best regards
Gunnar I. T.
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