| Products > Test Equipment |
| Most accurate signal generator |
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| Protegimus:
I know it blows your budget in this instance, but longer term you could look to something like the QuantAsylum QA403 https://quantasylum.com/collections/frontpage/products/qa403-audio-analyzer Very high specification for very reasonable money. |
| loop123:
--- Quote from: gf on April 01, 2024, 12:16:58 pm --- --- Quote from: loop123 on March 31, 2024, 10:53:58 pm ---I figured out the sine waves noises don't merge into one another because they don't affect the past. And at 1kHz amplifier setting. The noises of 50Hz vs 900Hz is identical because making it pulse faster (higher frequency below 1kHz) doesn't produce more noise. And I want to test this. --- End quote --- Sorry, I can't follow your thoughts. What do you mean with "noises of 50HZ vs. 900Hz"? You have noise, and you have your wanted signal. Just consider them as two independent signals. At the end, noise and wanted signal simply add up. The noise does not change if your wanted signal changes. You don't get a "different noise" if your wanted signal is 50Hz or 900Hz. Nevertheless keep in mind that your noise is not white, but your amplifier also suffers from 1/f noise at low frequencies, and that you deal with bandwidth-limited noise (~1kHz). Both imply that your noise is not independent and identically distributed, but it is autocorrelated. So the deformation of the waveform due to noise (if you zoom-in) will definitively look different for a 50Hz sine wave signal and for a 900Hz sine wave signal. I have attached example plots for 1kHz-bandlimited (2nd order Butterworth) white noise and 12dB SNR. Note that for the 900Hz signal, the noise mostly affects the envelope. Keep in mind that these plots are still not represenative for the noise of your amplifier. --- End quote --- What is meant by bandwidth-limited noise at ~1kHz. I googled it but the articles not even clear. At what frequencies do the bandwidth-limited noise does not dictate anymore? meaning when noises would be white and would appear identical at that frequency vs 900Hz? Also you mean 50Hz fall under the 1/f pink noise? At what frequencies would it no longer ruled by 1/f noise? I still don't own the $3000 software of the USBamp so can't test it with input shorted. Also it's completely software based with usb output and not like the analog output of the other one (BMA). How can you test Referred to Input noise with something like in the following software?? The above uses sine wave generator of 10uV, 50Hz. My Netech generator only has up to 0.1Hz, 2Hz, 5Hz, 50Hz, 60Hz output, none above. This is reason I was asking what noise would look like at 900Hz because I'd like to know how resolvable the peaks are and whether worth it spend $3000 on their software. In your waveforms, why does your 900Hz no longer have the same noise as your 50Hz? Because 900Hz are no longer have bandwidth limited noise and no longer dominated by 1/f? You mean if the my simulator can produce 900Hz, 10uV. The noises would be like your 900Hz? --- Quote ---To get a more representative picture, can't you record the noise floor of your USBamp (e.g. with Audacity, as you already did it with your other amplifier) and then use Audacity to add an artificial sine wave signal to the recorded noise in order to see what you would get? --- Quote ---Supposed my signal is 1V and I want to convert it to 10uV. --- End quote --- That's a factor of 100,000 or in other words 20*log10(100000) = 100dB. --- Quote ---What button or number should I press? --- End quote --- The enabled stages simply add up. Example: If you turn on 20+16+2, then you get 38 dB. --- Quote from: nctnico on April 01, 2024, 11:33:24 am ---That is an option but the step attenuator allows to make many different levels quickly which is handy while experimenting. --- End quote --- The OP was very much focused on accuracy. The chosen step attenuator is likely not a precision device. I wonder what total accumulated uncertainty can be achieved for the involved components (generator's no-load voltage, generator's output impedance, 8 attenuator stages, and the terminator impedance). I have doubts that we are still within 1% at the end. --- End quote --- |
| nctnico:
--- Quote from: gf on April 01, 2024, 12:16:58 pm --- --- Quote from: nctnico on April 01, 2024, 11:33:24 am ---That is an option but the step attenuator allows to make many different levels quickly which is handy while experimenting. --- End quote --- The OP was very much focused on accuracy. The chosen step attenuator is likely not a precision device. I wonder what total accumulated uncertainty can be achieved for the involved components (generator's no-load voltage, generator's output impedance, 8 attenuator stages, and the terminator impedance). I have doubts that we are still within 1% at the end. --- End quote --- Realistically: with the OP's limited budget reasonable accuracy (say 0.1%) is going to be impossible to achieve. And from OP's recent posts it becomes clear that the question is not about accuracy at all but signal to noise ratio. But even then, with some effort and an sensitive AC voltmeter, you can measure the input & output voltage of the attenuator and adjust the generator's level to compensate for the actual attenuation. All in all it should be possible to get 1% or better accuracy using this setup. It just takes calibration. Only real problem is temperature drift. Keep in mind that fixed RF attenuators may have an accuracy +/-0.5 dB (or even worse if I take a quick look at Mini Circuits' products). +/- 0.5dB is over +/- 5% in amplitude error. |
| JeremyC:
--- Quote from: loop123 on March 25, 2024, 09:11:30 pm --- --- Quote from: radiolistener on March 25, 2024, 02:25:32 pm ---I think SDG6022X signal accuracy should be good enough for amateur needs. https://siglentna.com/product/sdg6022x/ But its performance is not the best. So, if you want better performance, there is may be a sense to look for some specialized signal generator for your needs? What do you mean when talking "most accurate"? Less noise / less spurs / high dynamic range? If you're interested in precise amplitude, then there is a sense to look for RF generator. They have pretty clean sine output and allows to setup calibrated amplitude. But note, all signal generators have fixed output impedance, usually 50 Ω (sometimes there is a switch between 50 Ω and 600 Ω). And if your load is not 50 Ω, then you're needs to recalculate amplitude, that is normal and expected behavior. --- End quote --- The use is specifically to test the E1DC Cosmos ADC to see if for example it's 0dB corresponds to 1.7V or 1.8V in its lowest setting (with best dynamic range). Just to test its overall accuracy. My present 2 signal generators don't even produce output where I can be certain it's 1V or 1.5V for example. So I need one where I can produce accurate 1.7V or 1.8V to see which voltage would clip it and establish the baseline because different units vary according to the manufacturer. I didn't know choosing signal generator is that complicated that is why didn't post the entire picture below in the original message. In the following is the -128dB noise floor of my E1DA I tested using REW RTA. My budget for the stand alone signal generator is less than $200. Please recommend which one specifically I should get knowing my requirements. Thanks. --- End quote --- Why you are not using the signal generator from the REW suite? I'm guessing DAC in your computer is 24bit and in theory you have 144dB dynamic range. Link to documentation: https://www.roomeqwizard.com/help/help_en-GB/html/siggen.html#top |
| loop123:
--- Quote from: JeremyC on April 02, 2024, 12:21:52 am --- --- Quote from: loop123 on March 25, 2024, 09:11:30 pm --- --- Quote from: radiolistener on March 25, 2024, 02:25:32 pm ---I think SDG6022X signal accuracy should be good enough for amateur needs. https://siglentna.com/product/sdg6022x/ But its performance is not the best. So, if you want better performance, there is may be a sense to look for some specialized signal generator for your needs? What do you mean when talking "most accurate"? Less noise / less spurs / high dynamic range? If you're interested in precise amplitude, then there is a sense to look for RF generator. They have pretty clean sine output and allows to setup calibrated amplitude. But note, all signal generators have fixed output impedance, usually 50 Ω (sometimes there is a switch between 50 Ω and 600 Ω). And if your load is not 50 Ω, then you're needs to recalculate amplitude, that is normal and expected behavior. --- End quote --- The use is specifically to test the E1DC Cosmos ADC to see if for example it's 0dB corresponds to 1.7V or 1.8V in its lowest setting (with best dynamic range). Just to test its overall accuracy. My present 2 signal generators don't even produce output where I can be certain it's 1V or 1.5V for example. So I need one where I can produce accurate 1.7V or 1.8V to see which voltage would clip it and establish the baseline because different units vary according to the manufacturer. I didn't know choosing signal generator is that complicated that is why didn't post the entire picture below in the original message. In the following is the -128dB noise floor of my E1DA I tested using REW RTA. My budget for the stand alone signal generator is less than $200. Please recommend which one specifically I should get knowing my requirements. Thanks. --- End quote --- Why you are not using the signal generator from the REW suite? I'm guessing DAC in your computer is 24bit and in theory you have 144dB dynamic range. Link to documentation: https://www.roomeqwizard.com/help/help_en-GB/html/siggen.html#top --- End quote --- I used Microsoft Surface Pro 2017. How is its DAC? if bad. What external usb DAC can I get? |
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