-------- In message <[email protected]>, Magnus D anielson writes:
>What does exists is a formula for how a single sine spur would produce >ADEV. A FM deviation with low enough modulation index creates two >side-bands of opposite sign but same amplitude. I find the easiest way to wrap my head around this is to think about measuring Adev by timing zero-crossings. If we had a perfect zero-crossing detector, perfect AM would not matter, because perfect AM does not move the zero-crossings. But in theory at least one electron, and in practice many, must run the opposite direction before we can detect the zero-crossing, so even perfect AM matters in practice. (Interesting detail: Measuring at high impedance may be smarter than at 50 Ohm impedance) For FM or PM there is no loophole: They move the zero-crossings and that's that. Depending on the modulation signal, there may be moments where the zero-crossing is "where it should be", for instance if the modulation is sine or triangular, but not if it is a signed square wave. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
