[time-nuts] Sound Card Spectrum Analyzer

Gerhard Hoffmann dk4xp at arcor.de
Fri Feb 19 07:35:15 UTC 2010


Bob Camp wrote:
> If the noise is "known flat" it's a good way to check system bandwidth. Some means of checking response is indeed very necessary. 
>
> Not switching the preamp is indeed a good thing. The sound card does not have the range of the 3561, so with the sound card the beat note absolutely require a switch. The switch adds a second calibration step at audio. 
>
> To calibrate level, the levels of both the noise and carrier need to be well known. For a "basement system" the measure the slope as it crosses zero is likely more accurate. That of course assumes that you do the audio gain and response stuff properly. 
>
> Many of the free applications that are out there will put a tone out of the card and track it back into the card. That should at least provide a tone to work with. I also should be something that can be fairly easily verified. The issue of mixer output impedance is still a little tricky without RF noise loading. 

One of those 346 A/B/C noise sources with 15 dB excess noise should be 
about right
to check the noise floor.

<http://freenet-homepage.de/dl4yhf/spectra1.html>
 looks like a good FFT program.

regards, Gerhard



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