# Questions tagged [complex]

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### How to demodulate Binary Offset Carrier Signal?

I need to modulate and demodulate a BOC (Binary Offset Carrier) modulated signal. I tried starting with: ...
• 3
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### Orthogonal signals basics [closed]

Suppose we have 2 orthogonal signals $x_{1}(t)$ and $x_{2}(t)$ and we add them up. Can we always say that the resulting signal will be of this form: $$x_{3}(t)=x_{1}(t)+jx_{2}(t)$$ ? If that is true ...
841 views

### How can we treat real signal as imaginary?

I'm studying MRI and I couldn't understand this assumption(?) The sentence 'The signal from one channel is no more or less "real" than that from the other channel.' Does not make sense to ...
467 views

### (graphic) Relation between FFT and complex signal

I have a complex signal with a frequency between 0 and 16 (16 not included). I have made four plots (in python) to show four examples. For each example I provide the signal, its FFT in both real, imag ...
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1 vote
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### Alternative to Hilbert Transform

I have an digital system that needs an analytical signal of length (in time) T. The system is sampling the analog signal with time interval delta t such that T / delta t = 128. So I have 128 samples. ...
• 195
1 vote
26 views

### please help me solve the question which proving X[N-k] is the complex conjugate of X[k] [closed]

Show for the DFT that if all x[n] are real, then X[N - k] is the complex conjugate of X[k] for k > 0. (i.e. if X[k] is a + bi, then X[N - k] is a - bi)
• 11
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### When converting real samples to complex, how much energy does the signal lose?

Assertion: When converting real samples to complex, the resulting complex vector will have half the energy of the original real vector. Simulation in Python tells me this is true. However, my proof ...
674 views

### How can I generate a OFDM baseband signal with the output of the ifft?

I have some understanding problems with OFDM. I think I have understood most of the theoretical concept. At the moment, I am trying to write some Python code to simulate the transmitter part. This is ...
68 views

### Frequency Translation after FIR Filter

I am trying to translate a signal to baseband by multiplying by the complex exponential. The issue is when I do the calculation in MATLAB the signal seems to disappear. I originally thought the signal ...
820 views

### Frequency shifting with complex exponential

I'm trying to frequency shift a sine wave at 50kHz by using a complex exponential at 15kHz. I should be getting an FFT with a peak at 65kHz. Instead I'm getting a strange looking peak at 52.4kHz. ...
518 views

### Plotting Constellation Diagrams

I'm working with some IQ data from the paper A Wideband Signal Recognition Dataset. Specifcally I've been trying to plot the constellation diagram for some the modulations within the dataset, however, ...
61 views

### System Characterization: multiply imaginary component by scalar

I tried solving a test question that frankly stumped me. If you could explain to me the solution I’d be really grateful. Given $a, b \in \mathcal{R}$ the system $R_v$ takes the complex input $a + bj$ ...
208 views

### Problem using BladeRF using two RX inputs

I am working with BladeRF xA4. I have a signal generator at 1.5GHz modulated with cos(2pif_mt)+jsin(2pif_m*t). This generator is conected to a signal splitter. Next to the splitter two cables are ...
213 views

### Complex Envelope

Two signals have arrived with different phases. The sum signal is given by $$x(t) = A\cos(2\pi f_ct) + B\cos(2\pi f_ct + \theta)$$ What is the complex envelope of $x(t)$? Need advice on how to get ...
43 views

### Are real exponential signals still eigen functions of LTI systems?

I know that complex exponentials are eigen functions of LTI systems for example $e^{j2t}, e^{-j5t} , e^{j8t}$ . If we can define complex exponential as $e^{st}$ where $s$ is a complex number. Can we ...
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323 views

### is this signal is perodic?

What is the time period of $$x(t) = 7 e^{\jmath(5t + \pi/2)} + 10^{\jmath(7t + \pi/5)}$$ ? X(t) is the combination of two functions. one is the natural logarithm base, $e$, and the other is 10. if ...
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1 vote
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### Allpass filter with delay of $\pi/2$ for only negative frequencies

I would like to design a complex and causal allpass filter with delay of $\pi/2$, but only for negative frequencies. The positive frequencies should have a delay of 0. Is that possible and how I ...
• 423
95 views

### Are there any recommended filter types for passband frequencies near Nyquist?

Is there a recommended filter type for frequency bands near the Nyquist frequency? I have been trying to design complex passband filter with passband $[0.8 ~~1]$ ( where $1$ corresponds to the ...
• 129
20 views

### find gamma from complex form?

In $$e^{j\pi/\gamma x}=c$$ if $x$ and $c$ are known, how to find $\gamma$ since if we break to sine and cosine term the problem becomes more complicated. This is a complex value and $j$ indicates ...
41 views

### Different complex pairs giving same magnitude and phase

I am trying to fit data of magnitude and phase to get complex pairs(for FFT), but I think it would be a wrong approach as different pairs of complex numbers can give same amplitude and phase , is my ...
117 views

### FM generation with complex numbers

Background To generate a sine wave the straight forward way is to call the sin method for each data point: Iteration (pseudo code): ...
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