Joel Kolstad wrote:
Roy,

"Roy Lewallen" wrote in message
...
This is covered in detail in _Modern Spectrum Analyzer Theory and
Applications_ by Morris Engelson (Artech House, 1984).

Does Engelson's idea of "modern" include digitizing spectrum analyzers, which
have already taken over most of the mid- to high-end of test equipment and --
as with digital scopes -- will most likely soon be in all but the lowest of
the low-end of instruments?

No, the book was written before those came about. I fudged a little by
qualifying my posting with "conventional" spectrum analyzer to exclude
newer technologies, but it sounds like "conventional" is rapidly
advancing to become the newer types.

I got out of the SA development world just as digital techniques were
beginning to develop -- my last patent (# 5,629,703), in fact, dealt
with a way of reducing distortion in an A/D converter intended for use
in a SA-like instrument. At that time, we were anticipating doing a
conventional sweeping down-conversion, then digitizing it at a 25 MHz
IF. Predictably, the digitization point has been moving toward the front
of the instrument since then.

I haven't followed the technology since, but I'm sure the new ones use
sampling techniques combined with an FFT, which is another way of
imperfectly representing what the real spectrum is like. (Actually, you
can never perfectly represent the spectrum of a real waveform, because
any spectrum which is finite in frequency span has to have existed for
an infinite time. Any modulated waveform is way outside this category.)
Sampling produces its own, different, sorts of artifacts which are
different from the ones produced by sweeping, although there are some
similarities. You have to be at least as careful, and maybe more so, in
interpreting a sampled waveform as one which is from a swept filter.

I'd be surprised if someone hasn't written an equivalent book to cover
the new type instruments, although a lot of the material in Morris'
books is still valid and teaches a lot about the nature of spectra.
Morris was the driving force behind Tektronix's entry into the spectrum
analyzer market, and the group's chief engineer and architect for a long
time. He'd retired by the time I joined the group, and I only met him
when he taught a couple of one-week courses based on his books. He's
truly one of the experts in the field.

Roy Lewallen, W7EL