Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Tom Lee


If you ever wish to examine the spectral content of a signal, you need an SA. Using a scope's presentation of a sinusoid, you'd be hard-pressed to resolve distortions below a percent, and you'd only do that well for certain types of distortion, and if your eyeballs and neural net are pretty damn well calibrated. A properly designed spectrum analyzer can resolve distortion levels in the ppm range (and still better ones exist). Better still, you see the nature of the distortion -- e.g., is the distortion dominated by a certain harmonic or group of harmonics? Is it not distortion at all, but interference or power supply noise creeping into the system? Etc.

So, depending on context, either a scope (for volts vs. time) or a spectrum analyzer (for volts vs. frequency) may be the right tool. If you have both, you've got both domains covered.

I should mention that some digital scopes have an FFT capability, giving you something that looks like what a spectrum analyzer would present. But there are many tradeoffs in trying to make a scope also act as a decent spectrum analyzer, so most scopes are not decent SAs. But if the software comes for free, one cannot complain too much, as long as one is aware that the instrument may present a screenful of lies.

-- Cheers,

Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 12/7/2020 23:54, Jeff Dutky wrote:

I've had a look at the TinySA home page (, watched several of the recommended videos, and I'm sold.

I've just got one question: aside from using it as a signal generator, what would I DO with a spectrum analyzer?

-- Jeff Dutky

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