Whether or not you should care about positive and negative frequencies depends on how you got your time-domain data and your application. If your samples are just real numbers, then you can ignore half the spectrum and double just one side.
If your samples are complex I and Q , you need both sides of the spectrum since the spectrum is asymmetric. For applications such as simple real-valued filters, you can just use cosines and look at a single-sided spectrum. In that case you care about both sides of the spectrum. For more information about the power spectrum and complex sampling, check out this post on the power spectrum. Complex signals can be represented as sines and cosines; real signals can be represented with equivalent complex representations.
Look up how the Hilbert Transform works and is used. Keep your eyes peeled for a post on the Hilbert Transform in the future. Special thanks to Santosh for suggesting this topic!
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Are man-made constructs part of nature itself? If so, then does something that is man-made need to be physical to be part of nature? Math is math and math is used to describe our physical world. That said, to answer your question of wanting some physical analogy that can be described with negative frequency consider a spinning bicycle wheel.
We will use mathematics to describe its rotation both in direction and rate of change. Similarly a rotational change in the clockwise direction represents a negative angle. With respect to a known given fixed point in time and space if you assume a time-space coordinate system , a negative frequency sine wave is simply the negative of a sine wave or sine function basis vector that starts with a phase of exactly zero at that same exact point in time.
The fixed point in absolute time can also be defined to be periodic with reference to a given fixed frequency, give any one fixed point. Or you can use a given phase of another given reference sinusoid at the identical frequency to create you train of periodic fixed phase reference points in absolute time and space. The even component is symmetric around the reference point and thus makes to difference with respect to the direction of time.
As with special relativity, two observers using two different reference frames or clocks can end up with two different measurements of phase, thus two different ratios of positive to negative frequency.
Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Does negative frequency actually exist or it is just theoretical?
Ask Question. Asked 1 year, 7 months ago. Active 1 year, 1 month ago. Viewed times. But I have one query Does negative frequency only exist theoretically or does it actually exist in nature and can be measured?
Improve this question. Can you be more specific about what you didn't understand about the answers? Whether it is theoretical only depends on your interpretation. As soon as you measure a sine wave to know its periodicity, you know it is the sum of two complex sinusoids, and, therefore, yes negative frequency can be measured in that sense.
Add a comment. Active Oldest Votes. Improve this answer. MBaz MBaz Regarding rotation, I guess the decision was made by the ancient Greeks when they defined a positive angle in the counter-clockwise direction. Show 11 more comments. And if we were dealing with polarized light, the same argument supports the model of linearly polarized light being comprised of equal intensity left and right hand circularly polarized components. Thomas A. Groover Thomas A.
Groover 29 2 2 bronze badges. Dan Boschen Dan Boschen Does it describe something in the measurable universe? Hm, good question. Does my brain belong to that universe? I'd argue it does. But you could also suggest with a standard broadcast that it is indeed measuring the instantaneous frequency which is going negative and positive related to the carrier. Nothing we would hear any differently however.
Just as you can't measure power going through a device's power cord with just one multimeter: It's a very physical thing, but you need to observe multiple things simultaneously, and relate them. Show 2 more comments. I assume scalar. Thus no complex number exponentials allowed until after IQ heterodyning to something non-physical math , or into two physical channels of which the real sine component voltage can be inverted for a baseband negative IQ frequency. But you don't have to use that convention.
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