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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Re: Doesn't that depend on it being continuous? posted by Steve Eddy on May 17, 2005 at 19:30:08:
I know I'm not being that clear about this, but I can't think of another way to describe it.In FM, as I understand it, the frequency of the signal shifts over time. When it is not at the nominal frequency, then there is no "fundamental" at that nominal frequency (at that instant). The fundamental only shows up during periods of zero modulation.
Example: if you have a single-frequency sine wave modulated by another sine wave at a much lower freq, the display on the spectrum analyzer will show equal amplitude at all frequencies from the nominal center out to the maximum offset on either side. Right? Where is the fundamental? Is it the center?
This is quite different from, say, THD or IM, in which the fundamental ALWAYS exists at a constant frequency but the distortion artifacts are visble at others.
A spectrum analyzer attempts to give you a view of a signal in the freq domain rather than the time domain. This means it is not giving you time domain data by its very nature. In other words, it can't show you changes in time of the frequency-domain content. At best it can either give you an average over a time period or a snapshot.
BTW: If the jitter were NOT repetitive or cyclical, how could it be FM?
Peter
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Follow Ups
- Re: Doesn't that depend on it being continuous? - Commuteman 10:21:50 05/18/05 (1)
- Re: Doesn't that depend on it being continuous? - Dan Banquer 11:31:27 05/18/05 (0)
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