# signals and systems

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A signal is variable in  time domain , why we have to use transform tools(Fourier transform) to frequency domain?

if so  signal transformed what kind of characteristics we could get?

or In which way that transformed signal is useful ?

Thanking You

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To know the frequency content of the signal.

This can be useful to analyse the signal in order to design appropriate signal processing or to determine characteristics of the source or to detect faults (eg damaged bearings)...

It can also be useful to filter in the frequency domain, so specific frequencies can be filtered out.

It is also useful in image processing. JPEG eg throws out the high (spacial) frequencies to compress pictures while maintaining high quality.

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You have asked this in Engineering but the reasons are much wider than this.

1) Mathematical

We apply a transform to something to make the maths easier.

For instance the 'logarithmic transform  turns more difficult multiplication, taking in to addition.

To get our final result we also need the inverse transform to turn what we are doing back again.

2) Geophysical

So we take a function of time (the height of the tide) and transform it to the frequency domain to be able to predict future tide activity.

These we transform back to time to time to publish daily tide tables.

Earthquake analysis works in a simialr fashion.

3) Engineering

Laplace and Fourier transforms make the mathematics of electrical circuit analysis easier by turning differential equations (of the time varying voltages/currents in a curcuit) into simpler algebraic equations, which we can then solve.
Again we need the inverse transform to turn them back into useful solutions.

4) Astrophysics and Cosmology

The activity of pulsars, binary stars and many other heavenly observed phenomena can be analysed by these methods.

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On 25/07/2018 at 1:55 PM, sumanth said:

A signal is variable in  time domain , why we have to use transform tools(Fourier transform) to frequency domain?

if so  signal transformed what kind of characteristics we could get?

or In which way that transformed signal is useful ?

Thanking You

I think I will show you what a signal is with classical analogies before I attempt to answer your question, using terms that kids will enjoy and understand, yes?

A signal is a density of energy, and, energy is related to mass. If you carry a massive pulse of energy to another receptor, it will interpret it on it's reception of that 'electrical signal' and then charge the system with the power gauge, owing to the message of the pulse, or, 'logarithm of pulses,' okay? This is like a constant message, in the case of radios, or, cell hones, television signals and so forth from beacons sending this out. This is also found on a circuit board bus, for computers, by the way.

Now, your question owes to time? This would be the 'density' or 'charge' of the signal. Volts. If the signal is tuned to a different frequency, we can discern whether it is radio frequency, television and so forth, of course. This is for reading the signal, if it is too frequent, it will over clock the receptor, for that medium, and be ignored, but, if it is just right, it will be interpreted and used.

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15 hours ago, Brett Nortj said:

This would be the 'density' or 'charge' of the signal. Volts.

The unit of charge is Coulomb, not Volt.

15 hours ago, Brett Nortj said:

I think I will show you what a signal is with classical analogies before I attempt to answer your question, using terms that kids will enjoy and understand, yes?

A signal is a density of energy, and, energy is related to mass. If you carry a massive pulse of energy to another receptor, it will interpret it on it's reception of that 'electrical signal' and then charge the system with the power gauge, owing to the message of the pulse, or, 'logarithm of pulses,' okay? This is like a constant message, in the case of radios, or, cell hones, television signals and so forth from beacons sending this out. This is also found on a circuit board bus, for computers, by the way.

Now, your question owes to time? This would be the 'density' or 'charge' of the signal. Volts. If the signal is tuned to a different frequency, we can discern whether it is radio frequency, television and so forth, of course. This is for reading the signal, if it is too frequent, it will over clock the receptor, for that medium, and be ignored, but, if it is just right, it will be interpreted and used.

What you describe is modulating a signal on a high frequency carrier wave. No Fourier transform required (except perhaps to design or explain/visualise the mechanism).

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On 8/2/2018 at 6:39 AM, Brett Nortj said:

I think I will show you what a signal is with classical analogies before I attempt to answer your question, using terms that kids will enjoy and understand, yes?

A signal is a density of energy, and, energy is related to mass. If you carry a massive pulse of energy to another receptor, it will interpret it on it's reception of that 'electrical signal' and then charge the system with the power gauge, owing to the message of the pulse, or, 'logarithm of pulses,' okay? This is like a constant message, in the case of radios, or, cell hones, television signals and so forth from beacons sending this out. This is also found on a circuit board bus, for computers, by the way.

Now, your question owes to time? This would be the 'density' or 'charge' of the signal. Volts. If the signal is tuned to a different frequency, we can discern whether it is radio frequency, television and so forth, of course. This is for reading the signal, if it is too frequent, it will over clock the receptor, for that medium, and be ignored, but, if it is just right, it will be interpreted and used.

Patronising, poorly written and inaccurate.

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