> It is quite surprising that the 859xE series is spec'd about > 10-15 db worse on phase noise than the comparable 856xE instruments. I > wonder if this difference exists in the performance
Yes, and I just documented it. See my earlier post with the .GIF attachment. > or just marketing > domains and what the actual differences are in the implementation that > accounts for it. Usually phase noise in a synthesizer comes down to one question: "What's the N factor?" The older HP analyzers, dating back to the 8554/8555 plugins for the 141T, stabilized their LOs by locking them with a sampler to a harmonic of a 1-MHz VCXO. You can imagine what N=2000-4000 or more does to the phase noise. I don't know if the 8590s used a similar synthesizer topology but it wouldn't be surprising. They may have been designed in a hurry; Tektronix came out with reasonably-good portable analyzers before HP did, and took a lot of business that historically belonged to HP. The 8560s use a completely-different synthesizer architecture with a much-lower N factor. I think they call it a "roller oscillator," where the synthesizer runs at something like 1/10 the frequency of the YTO. > This was poorly phrased - I perfectly well know why one is > interested in phase noise on LOs and other signals closer to the carrier > than 9 KHz (no question there for me at least) but what I meant is why > one would want to use a general purpose wideband SA for making > measurements between 0-9 KHz or so... when FFT based technology is > available and cheap and very high dynamic range with very tight filters. > (Obviously this means high end soundcard type devices on a PC platform > these days), It comes down to convenience, I think. (1) Most people already have an RF SA, many of which are perfectly usable down to 100 Hz or 1 kHz; (2) Commercial phase-noise packages don't talk to PC sound cards; and (3) Most people don't care about PN at offsets that their SAs won't cover directly. Add to that (4): Newer SAs are FFT-based anyway, and don't need an auxiliary FFT analyzer at all. -- john, KE5FX _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.