> I call it simply spectrum too, maybe I should have said
> magnitude/phase spectrum.
Now I'm confused. Magnitude spectrum is definitely my $|\text{DFT}|$;
but you're just looking for a plot of the DFT, right?
> Indeed i don't need imaginary part in this case because the spectrum
> is real
That implies that your time signal is 0-time-hermitian (symmetrical if
real)! In your /example/ that is the case, because you're only summing
up /cosines/, but it's not usually the case.
So I'd like to get back to my earlier question:
What is the purpose of this?
You can very simply implement this using
stream to vector -> FFT -> complex to real -> Qt Vector sink.
Again, not convinced that is what you actually *need*. It's just what I
understnad that you *ask* for.
Best regards,
Marcus
On 04/26/2017 07:23 PM, Fernando wrote:
> I call it simply spectrum too, maybe I should have said
> magnitude/phase spectrum.
> Indeed i don't need imaginary part in this case because the spectrum
> is real..... or not spectrum lines will be real numbers with + / -
> ...... or complex numbers with 0º/180º phase
>
> The representation I would like to get is this one
>
>
>
> or like this other
>
>
>
>
> So, this way could do what I want to do
>
>
>
> But I would like to print the magnitude/phase spectrm, but QT
> Frequency sink prints only the power spectrum
>
> Is there any GUI sink wich can print this?
>
> regards
>
>
>
> El 26/04/17 a las 16:15, Marcus Müller escribió:
>>
>> Hm, I'd call that /spectrum/, simply :) In any case, I don't fully
>> understand, then, how you'd circumvent the need for a real and
>> imaginary part. Your $X_k$ is complex!
>>
>> Cheers,
>> Marcus
>> On 04/26/2017 03:46 PM, Fernando wrote:
>>> 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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