Hi Like it or not, the mixer is a non-linear load. It also has a frequency dependence. Even with “saturation” levels, the slope can and does change. That’s the short list, as you dive into it, things get even more complex in terms of “might be” sort of issues.
How can you be in saturation and have the slope change ( it does sound unreasonable) ? The fundamental is not changing much (so you are in saturation). The harmonics of the fundamental are changing. Since the output is actually a triangle wave with rounded “corners” there are indeed harmonics very much present. The flat parts of the triangle wave are a “good thing” in this case. It makes the device linear over a bit wider range than a sine wave would provide. This gets you out of all sorts of nutty analysis concerning the noise being “to much” to measure with the device. It also relaxes the needed accuracy of the DC lock part of things. ( = slope of a sine wave changes quickly ….). You never really get away from the “to much noise” question. The common definition of phase noise is that it’s more than 60 db below carrier. That is really just the commonly used limit for “you may need to think about FM sidebands”. Yes, that’s another rabbit hole to wander down …. Bob > On Jul 8, 2022, at 8:32 AM, Erik Kaashoek <e...@kaashoek.com> wrote: > > Bob > This confuses me. >> The calibration of the system changes ( or can change ) each and every time >> you swap >> out signal sources. The levels are not going to be consistent setup to >> setup. Thus you >> calibrate each and every time you change out either device. > Assuming each source is saturating the mixer sufficiently (to be confirmed by > measuring the output level of the source into 50 ohm) I do not understand how > changing a source can change the calibration. Can you explain what is > happening? > Please keep in mind I'm not after 0.1dBc/Hz accuracy, +/- 5dBc/Hz would > already be great. > Erik. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com