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How do I convert a real baseband signal to a complex baseband signal?

To convert a real signal sampled at rate $2B$ to its complex baseband representation (sampled at rate $B$), you want to map the frequency content in the range $[0, B)$ in the real signal to the range $...
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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

fmcw radar sampling requirements

A quick scribble on paper shows that FMCW radar has a resolution of $$ \Delta d = \frac{c}{2b} $$ with $c$ being the speed of wave propagation (aka speed of light, essentially), $b$ being the ...
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5 votes
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Why is the carrier suppressed by AM-DSB-SC modulation?

It's a simple trigonometric identity: $$\cos(\omega_mt)\cos(\omega_ct)=\frac12\left[\cos((\omega_m+\omega_c)t)+\cos((\omega_m-\omega_c))\right]\tag{1}$$ Multiplying two sinusoids of different ...
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4 votes
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Quadrature modulation

If we take the complex baseband signal as $S(t) = I(t) + jQ(t)$ (which of course means that we have two separate wires on which the $I(t)$ and $Q(t)$ voltages appear), then we have a nice signal ...
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4 votes

Quadrature modulation

The idea is that you can transmit two signals, $I(t)$ and $Q(t)$, over the same bandwidth and at the same time, and still recover each independently of the other. The math is pretty simple. If the ...
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4 votes
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Possible to Derive Receive Signal Power from RSSI?

I also read this from a response to a USRP user's question about RSSI measurements: [The] Received Signal Strength [Indicator is] always relative to some signal model, incorporating ...
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4 votes

Real world application of signal sparsity?

Sparsity concept is extensively being used in computer vision and image processing. The Idea is that natural image can be pretty sparse when it is transformed to different bases. this bases can be ...
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4 votes
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How to accurately model wideband RF reflections?

So, to give you something to read up on first, the channel you describe is a Rician or Rayleigh channel, depending on whether you have a dominant line-of-sight path or not. So, as a first approach, ...
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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

Why is GPS 1575 MHz?

The technical decision was to use L-Band which extends from 1-2 GHz. The specific frequencies to use within L-Band depended on political decisions including existing allocations and users of those ...
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4 votes
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Why do ATSC channels need 6MHz of bandwidth when they're digital?

A key point is bandwidth is proportional to the symbol rate, or rate of change of the modulation. If the symbol is rectangular shaped, the spectrum is a Sinc function with the first null in Hz at the ...
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3 votes

If you had supersonic hearing, would you be able to hear the carrier wave of an AM radio station?

The AM or medium wave band extends from 526.5 kHz to 1606.5 kHz in Europe or 535 kHz to 1705 kHz in the US. Ultrasound (not supersound! :-) frequencies range from 20kHz and up: However, a bigger ...
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3 votes

Measuring signal phase difference between receivers

Preface First of all: Arduino might really not be the tool of choice here; with a 1MS/s max, and some something-in-between-8-and-16-effective-bits ADC, there's hard limits on what you can detect. I ...
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3 votes

fmcw radar sampling requirements

Your 2. is (as far as I know) the standard way to implement a FMCW radar. The major advantage of both the FMCW and the SFCW (which was mentioned in the comments), is the sample rate of the ADC is ...
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3 votes
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Why is In-phase Quadrature sampling not used to record and store digital audio?

It is because the audio signals are real and already at baseband. In contrast radio frequency signals are often represented as complex numbers once they are brought back to baseband. Real signals can ...
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3 votes
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Difference between slow, medium, fast AGC

I don't believe there is much more to it than that, especially noting that you are aware not to track so fast that you track out amplitude information for modulated signals where the amplitude is used ...
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3 votes
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Does Radio Communication Have to Account for the Doppler Effect?

Does radio communication have to account for the doppler effect? Yes. Would be pretty terrible if that wasn't the case: RADAR wouldn't work! Do moving objects such as planes and rockets have to ...
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3 votes

How a diode-detector affects to Frequency Response?

But what does detector in the frequency domain? Something really complicated. We get trained to think about signal processing almost exclusively in the frequency domain, and we forget that the ...
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3 votes
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The transmission distance of a signal

In principle, you can always test your channel and adjust your power according to the channel state before sending any signal. Each channel is always unique regardless of being in a city or in more ...
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  • 126
3 votes
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Is digital (discrete) SSB plausible?

Ah, basically everything modern could be understood as single-sideband. The name is > 100 years old and was based off the fact that traditionally, all you could do on RF is take a single real-...
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2 votes

Filtering out unwanted square wave (Radio: DCS/DPL signal)

If you know that it is a square wave, and the frequency is roughly constant, I would think about synthesizing an inverted copy of it and adding it to the signal. The remainder would be your speech, ...
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2 votes
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Real world application of signal sparsity?

Sparsity covers a wide range of concepts. It characterizes an object (a signal, a system, a function) for which their exists a representation (exact or approximate) whose dimension (number of ...
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2 votes

Real world application of signal sparsity?

A couple of example areas: Sonar beamforming - in many cases there are a small number of targets Radar processing - a radar image can be decomposed to a background and sparse set of point like ...
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2 votes
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Why is Error Vector Magnitude (EVM) measured as an RMS value?

You've got it – zero mean noise still has power. That power happens to be its variance. RMS of such signals thus happens to be the noise amplitude's standard deviation – and give a sensible number to ...
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2 votes

how to eliminate interference in the same center frequency

First of all, the CC1101 supports a number of other frequencies, so as a trivial solution, you can switch to using those. The other thing that you can do at the RF module level is to "shift" your ...
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  • 10k
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
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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

SDR spectrum anomalies

Periodic noise in an SDR spectrum is a common problem. One likely source is EMI or RFI from nearby electronics. The sources of EMI and RFI can be from computers, USB cables, networks cables and ...
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