Author Topic: Cheap and Small Dynamic Signal Analyzer?  (Read 2137 times)

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Online electrolust

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #25 on: August 19, 2020, 01:25:17 am »
NanoDSA!
 

Online maxwell3e10

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #26 on: August 19, 2020, 03:41:34 am »
AD4003 ADC and OPA828 input amplifier. Anyone has better suggestions?
 

Offline Berni

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #27 on: August 19, 2020, 05:15:48 am »
Sounds like a pretty good fit alright. Perhaps also add a DAC to also let it do frequency response or distortion measurement.

Pair it up with a ST MCU with hardware floating point to do the FFT. The more gruntry ones are fast enough to do live real time FFT with no gaps at a few MSPS. Slap a LCD on the front and you got a NanoDSA.
 

Online electrolust

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #28 on: August 19, 2020, 04:01:40 pm »
always best to start from requirements. THEN decide the components. The hard part is going to be the software.
 

Offline Berni

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #29 on: August 19, 2020, 05:41:11 pm »
Well if you are making something similar to the NanoVNA then the number one requirement is cost.

Hence you just pick the best components that the BOM budget will allow and squeeze the best specs possible out of those. But yeah most of the work here is indeed the software. Its not difficult to do but a lot of work to give it all the useful features of a DSA.
 

Offline gigavolt

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #30 on: August 19, 2020, 09:54:05 pm »
NanoDSA!

 ;D my thoughts exactly.  I'm surprised nobody has tried to do it yet, but I suppose that the combination of low frequency and low noise makes it difficult.
 

Offline Berni

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #31 on: August 20, 2020, 05:11:17 am »
NanoDSA!
;D my thoughts exactly.  I'm surprised nobody has tried to do it yet, but I suppose that the combination of low frequency and low noise makes it difficult.

Guess more of a problem is that very few people actually want one. They are perfectly happy with there existing Rigol scope.

The low frequency and noise is not that much of a problem, you just pick a really nice opamp for the AFE. More of a difficulty is getting a spurious free response over the whole range. The noise floor is so low that even the tinyest of signals show up as a spike. This means a great deal of care must be taken in the shielding and PCB design to avoid any power supply noise or digital signals from getting in there and showing up. For example in my diy sound card design i had a LDO become just slightly unstable, not enough to cause obvious problems or a huge sine wave on the output when when poked with a scope, but it was singing enough to produce a small spike in the FFT, was quite a hunt to find where it was coming from.
 
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Online KE5FX

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #32 on: August 20, 2020, 06:39:51 am »
For example in my diy sound card design i had a LDO become just slightly unstable, not enough to cause obvious problems or a huge sine wave on the output when when poked with a scope, but it was singing enough to produce a small spike in the FFT, was quite a hunt to find where it was coming from.

Let me guess, the part number contained the digits "1117"?
 

Offline Berni

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #33 on: August 20, 2020, 07:23:01 am »
Let me guess, the part number contained the digits "1117"?

Forgot what it was exactly but it was some fancy pants high PSRR LDO whos job was to prevent crap from getting into the sensitive front end. So yeah... you had ONE job.

As for 1117.. yeah i don't even need a scope anymore to tell when one of those damn things becomes a oscillator. Last time i started wondering why my board is making a whistling sound even when there are no switching regulators on it. Turns out it was oscillating so wildly that the ceramic capacitors around it started signing loud enough to be noticed even in a not so quiet room.
 

Offline 2N3055

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #34 on: August 20, 2020, 08:24:07 am »
Let me guess, the part number contained the digits "1117"?

Forgot what it was exactly but it was some fancy pants high PSRR LDO whos job was to prevent crap from getting into the sensitive front end. So yeah... you had ONE job.

As for 1117.. yeah i don't even need a scope anymore to tell when one of those damn things becomes a oscillator. Last time i started wondering why my board is making a whistling sound even when there are no switching regulators on it. Turns out it was oscillating so wildly that the ceramic capacitors around it started signing loud enough to be noticed even in a not so quiet room.

"The singing regulator", new Broadway show..... LOL...
Yep, I avoid them too...
 

Offline gigavolt

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #35 on: August 20, 2020, 03:26:56 pm »
Guess more of a problem is that very few people actually want one. They are perfectly happy with there existing Rigol scope.

That too, because ultimately the reason I would want it is for better noise performance/higher dynamic range, but in a much smaller bandwidth (<100 kHz) than my scope.  I'm guessing most hobbyists can "get by" with 8 bits.
 

Offline Frex

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #36 on: August 20, 2020, 04:42:16 pm »
Hello,

Just for information, I currently design such type a device.
It's a full open source 2 channels analyzer that use the LT2380-24,
a  24 bits 2MSPS high performance ultra low THD ADC.
It's not really a very low cost device and the full project is not yet finished.
(I'm writing the FPGA firmware for now).
Anyway, maybe that can interest some people.
I publish the project advancement on a DIYaudio thread HERE

The design has been firstly checked with tweaked EVM boards few years ago,
all details and history can be read on this other thread HERE .

Regards.

FRex

 
 
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Online maxwell3e10

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #37 on: August 20, 2020, 07:30:00 pm »
This is a cool project! I guess for a general purpose device one might make a more versatile input stage, with several different gain settings and a good single-ended noise level.
 

Online KE5FX

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Re: Cheap and Small Dynamic Signal Analyzer?
« Reply #38 on: August 20, 2020, 09:25:01 pm »
Very nice.  I was about to say that any effort along these lines needs to be multichannel.  I'm short on free time at the moment but will bookmark the diyaudio thread(s) for later perusal.  :-+
 


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