6 votes
Accepted

Why do we need to increase sampling frequency at the transmitter?

Three reasons to increasing the sampling rate further are 1) To relax the requirements of the post D/A conversion filtering for image rejection. 2) Increase signal SNR by spreading quantization ...
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5 votes
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Recommendation for good ressources on digital processing and D-QPSK

Wow, I'm honored by Matt L. doing what I'm often doing: Referring people to GNU Radio. The project actually has a list of recommended literature, but I don't know how well that'd fit you. It's ...
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5 votes

Why is phase range between $-\pi$ and $+\pi$ (instead of $0$ and $2\pi$)?

First, when you're talking angles, in DSP pretty much all angles are $\mod 2\pi$. So $2\pi \equiv 0$. Usually it's more convenient to keep angles on the interval $\left [-\pi, \pi \right )$, because ...
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  • 8,285
5 votes

Why is phase range between $-\pi$ and $+\pi$ (instead of $0$ and $2\pi$)?

It is just a convention, but it is useful in some cases. For example, the phase of the DFT of a real discrete-time signal is odd only if the angles are expressed in the range $[-\pi, \pi)$. Sometimes ...
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4 votes
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I/Q sampling with just one ADC

Is this an entirely stupid idea? No, but you've just came to the conclusion that instead of sampling complex, with Nyquist rate being the bandwidth, you should do twice as many samples. That simply ...
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4 votes
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Time Alignment of 2 Sensors Sampling the Same Signal with Different Hardware Delays

If the above is a good representation you should just try to infer when there is energy in the signal to align them. As it seems they start with nothing (Zero value). Then all needed is just to find ...
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4 votes
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Compare the quality of IQ data from different Software Defined Radios (SDRs)

First and foremost, I would recommend against over the air testing for this given the significant challenge in really being able to provide the same signal to each radio (since you have both temporal ...
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3 votes
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Use of I/Q representation for unmodulated Rx Signal

If you are "observing" the source, this implies there is some sort of information you are looking to get out of it, whether it be the total background noise, interference levels etc. Do you ...
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2 votes
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Trouble with time-syncing two radio signals using cross-correlation

It will work when you take the 2nd gradient of the signals: ...
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  • 36
2 votes

why transmitting a long pulse its spectrum gets spread?

this is John BG 1.- GFSK is not same as single tone According to the CC1101 specs you refer to, the C1101 uses GFSK. GFSK varies the varrier frequency, therefore the spectrum cannot be a delta. ...
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2 votes

Technical Term for the Sum I + Q

This can be implemented, without needing to access the real and imaginary parts of $z$ individually, by writing $$\operatorname{Re}(z) + \operatorname{Im}(z) = \frac{(1 + i)(z^* - iz)}{2},$$ where $...
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2 votes
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How can an SDR recover a high-frequency signal?

The high-frequency (RF) section of an SDR is all analog. Typically, the analog receiver downconverts the RF signal to an intermediate frequency that is within the Nyquist range of the ADC. As Stanley ...
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2 votes

Symbol time offset simulation

If you postulate that receiever's clock is perfect, then you want to make the transmitter send symbols every $T_s \pm \varepsilon$ seconds, where $T_s$ is the symbol period according to the receiver. ...
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2 votes
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What a SDR can (and cannot) tell about a received signal's power/energy

From what I've gathered, an SDR is not an instrument capable of measuring a signal's power/energy and it needs some specific calibration to correctly measure power/energy. Is that true? Hm. somewhat ...
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1 vote

GNU Radio, Frequency Hopping Spread Spectrum for High Hopping Intervals

No you cannot change the carrier frequency of your local oscillator instantaneously. The RF local oscillator will be in a Phase-Lock Loop (PLL) circuit to a low frequency reference (to provide ...
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1 vote
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Confusion about the frequency of a signal recorded with a USRP

The USRP is taking a frequency band of width 256 kHz centered on 710 kHz, and downconverting it to baseband. Whatever is in that band will appear in the USRP output. To be specific, the band that the ...
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  • 13.8k
1 vote

Why is phase range between $-\pi$ and $+\pi$ (instead of $0$ and $2\pi$)?

I have thought about some points which could help find the answer: 1- I think there might be something related to $\operatorname{arctan}(x)$ which is continuous in $(-\pi/2 \ \ \pi/2 )$ but I am not ...
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  • 75
1 vote

SDR Dongle, 2MHz Bandwidth related to Fs but bandwidth range 50-2000 MHz

SDR is not applying a lowpass (baseband) sampling on its RF input, instead it effectively employs a band-pass signal sampling. According to Shannon-Nyquist baseband sampling criteria, the bandwidth of ...
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1 vote

Do we have to insert the DC null in OFDM when using RF direct sampling ADC architecture?

RF direct sampling architecture? Will there be DC offset? No, since the center of your signal doesn't end up on DC, so there's no DC offset. If not, then is it okay not to insert a DC null? yes. ...
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1 vote
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Calculating dBFS for I/Q

The sensible way here is to realize that each complex sample has a magnitude $|z|=\left\lvert \Re z + j \Im z\right\rvert = \sqrt{\left(\Re z\right)^2+\left(\Im z\right)^2}$. In your case, the ...
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1 vote

Radio Signal Stationarity

When working with such an RF signal, numerically transformed to a stochastic timeseries, to which extent can I consider the signal to be stationary? That depends on your signal model. We can't tell ...
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1 vote

Can a software defined radio with a frequency range of 300 MHz – 3.8 GHz detect AM (535 to 1705 KHz) and FM signals (88 to 108 MHz)?

For those given specs, without additional hardware (upconverters) or modifications to the SDR circuit, it's not possible to detect AM or FM (88-108 MHz) range of frequencies. As you might have also ...
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1 vote

Technical Term for the Sum I + Q

After some thinking, I would could this a cartesian sum. It borrows from the notion of cartesian sum of two sets, here $\mathbb{R}$ (real part) and $i\mathbb{R}$ (imaginary part): if $x\in X$ and $y\...
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1 vote

Technical Term for the Sum I + Q

There's no specific term, as far as I know, but it's a very common operation with quadrature mixing. It's the result of taking the real part of an analytic signal. You have a complex baseband signal $...
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1 vote

How can the I and Q components of a quatrature signal be different from each other (apart from the 90º phase shift)

In terms of visualization, I think you may be confusing phase shift and delay. In the case of a single-frequency complex exponential , a plot of the imaginary part appears to be delayed from the real ...
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  • 486
1 vote

How can the I and Q components of a quatrature signal be different from each other (apart from the 90º phase shift)

Let's start from the beginning. Given a real signal to a quadrature circuit, two components are generated, I, the real component, and Q, the imaginary component, which is the same as I, only it has a ...
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1 vote

How can the I and Q components of a quatrature signal be different from each other (apart from the 90º phase shift)

You are mistaken in your 2nd paragraph. The I and Q components are not always identical with a 90 degree phase offset. Instead, they are usually generated by multiplying some real or complex signal ...
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