Hi!.
I think the amplitude spectrum is the DFT:
{\displaystyle {\begin{aligned}X_{k}&=\sum _{n=0}^{N-1}x_{n}\cdot
e^{-i2\pi kn/N}\\&=\sum _{n=0}^{N-1}x_{n}\cdot [\cos(2\pi kn/N)-i\cdot
\sin(2\pi kn/N)],\end{aligned}}}
So, it has sign. The power spectrum is the absolute value so it has no sign.
I wish to be able to see the difference in the spectrum between this two
signals below. If the signal generators are A and B, A+B and A-B are
different signals, but in the power spectrum we see them as the same
signal, so I woul like to be able to difference one from the other from
their spectrum.
regards
El 26/04/17 a las 09:52, Marcus Müller escribió:
>
> Hey Fernando,
>
> not quite sure I get what you need; I'd say the Amplitude Spectrum
> you'd be looking for is
>
> $$A_{|\cdot|}[f]=|X[f]| = \left\lvert\sum_{n=0}^{N-1} x[n]\cdot
> e^{j2\pi \frac {nf}N}\right\rvert $$
>
> or, rather, the decibel representation of that. There's no way to get
> a negative number out of the absolute of something – it's by
> definition a positive real number.
>
> Now, we could also use our freedoms to define our amplitude spectrum
> to take the shape
>
> $$A_\text{signed} = s(X[f]) |X[f]|\text{ with }
> s(X[f])=\begin{cases}1&\text{for } -\pi \le \angle X[f] < \pi \\ 0
> &\text{else.} \end{cases}$$
>
> But: that's really only useful if you have phase-coherent reception –
> as an analytic tool for an unsynchronized observation of the spectrum,
> it doesn't help you much, since you have a random $\angle$ due to
> having random relative phase.
>
> So, maybe it'd be a good idea to formulate what purpose you're doing
> this for :) You can, indeed, tell 180° out-of-phase signals apart by
> this, but I'd argue that being 180° out-of-phase, for the most things
> I can think of, is only meaningful on one and the same frequency – and
> hence, I'm not quite sure this is what you're looking for!
>
> Best regards,
>
> Marcus
>
>
> On 25.04.2017 12:01, Fernando wrote:
>> Hello.
>>
>> Yes, with Time sink I can see the difference, but if the signal is
>> compound of some other signals (for instance signal=1K/amplitude +1
>> +2K/amplitude -1 +3K/qamplitude +1 +4K/amplitude +1 ) i would like
>> to see the 2k signal as -1 amplitude, but in the power spectrum it
>> will appear as possitive and in the QT time sink it is very difficult
>> to see the signal as it is a complex one.
>>
>> regards
>>
>>
>> El 25/04/17 a las 10:57, Jinyang Lee escribió:
>>> Hello Fernando,
>>>
>>> I think the QT GUI time sink displays the relationship between time
>>> and amplitude. You can see the signal through it. But when I use the
>>> channel model block,the QT2 can see the signal which is zero.
>>> Enclose is running result with channel model and with channel model.
>>>
>>> Regards,
>>> Lee
>>>
>>> 2017-04-25 15:45 GMT+08:00 Fernando <ferna...@samara.com.es
>>> <mailto:ferna...@samara.com.es>>:
>>>
>>> Hi.
>>>
>>>
>>> Is there a way of visualizing ampitude spectrum (with + and -
>>> signals)
>>> instead of power spectrum?
>>>
>>>
>>> regards
>>>
>>>
>>>
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>>>
>>>
>>
>>
>>
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>
>
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