Questions tagged [quadrature]
The quadrature tag has no usage guidance.
91 questions
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Are amplitude (AM) and phase (PM) noise truly unambiguous?
I've been reading a lot on phase noise and phase detection techniques, especially IQ detection. In the literature, it is made clear that phase fluctuations $\varphi(t)$ and (fractional) amplitude ...
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Do all phase quadrature signals form orthogonal pairs with their in-phase versions
I have been studying analog modulation, in that i found a concept of quadrature carrier multiplexing which says that two baseband signals with possibly different bandwidths can be modulated to occupy ...
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Analog FM & IQ modulation
I am exploring the possibilities of IQ modulator. I want to do analog FM modulation (range $0$ to $5 ~ kHz$) using IQ modulator.
So far, I can modulate the signal digitally inside of the STM32 ...
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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, ...
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MSK without I/Q data
I just started a while ago with DSP and slowly staring to understand the concept of I/Q and what it means. I successfully could decode some bfsk, bpsk and wanted to move to msk which as not easy to ...
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Error in complex signal with imperfect quadrature phase and amplitude (textbook question)
I am working on the following problem:
I have a solution that I am pretty confident is correct as have checked the output in python. However, it is long and the entire time I was answering the ...
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Amplitude modulation in SDR [closed]
I understand the theory of amplitude modulation. However, I couldn't understand it's implementation in SDR, which use IQ data, and I would like to learn
end to end amplitude modulation system in ...
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Is the phase of a IQ point related to the local oscillator frequency?
When considering a direct conversion SDR receiving or emitting architecture, we can "represent" the received or transmitted signal as the sum of two components, the I and Q component.
Each ...
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What tricks can one play on a bandwidth-limited IQ modulator?
I would like to create a pulsed RF signal that has a carrier frequency of 2 GHz by IQ up-conversion. The pulse should be 2-4 ns long. The carrier phase has to jump by 90° in the centre of the pulse. ...
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How does the quadrature sampling lower the sampling rate?
According to this tutorial, by exploiting quadrature sampling with IQ signals, we then have the benefit that each ADC operates at half the sampling rate of standard real-signal sampling (This ...
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How are discontinuities in quadrature modulated signal QAM physically produced?
In quadrature modulated signals, for instance:
I am unclear how the "discontinuities" in the waveform at the junction of each data point can be physically produced?
Taking a speaker as an ...
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Doubt on Signal Processing Step
I am using a Radar Sensor. So applying Signal Processing on the Radar Sensor Data. PrevSample and PastSample are Radar IQ samples for a present and previous Sweep detecting tiny movement. In the ...
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Interpolating Filter for Quadrature Detector with one ADC
Single ADC is sampling at 16000 Hz the I and Q outputs of quadrature detector. So each I and Q signal is sampled at 8000 Hz, with phase offset 90 degrees between them. Bandwidth of interest is 3400 Hz....
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546
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Quadrature Detector with a single ADC
I have a quadrature detector, which provides I and Q baseband signals with 4 kHz bandwidth, set by detector's LPF. I digitiize them on two ADCs with sampling frequency 48 kHz, make Hilbert ...
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Performing IQ imbalance correction on sampled quadrature signals
What are the techniques which can be used to perform digital IQ amplitude and phase correction in a wideband receiver system when input signals can be of unknown different frequencies and occupy ...
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How to resolve some inconsistencies in the mathematical model for the narrowband fading channel?
I am reading Wireless Communications by Andrea Goldsmith. There the author mentions that for narrow band channel the received signal can be given as:
$$r(t)=\text{Re} \left\{u(t)\text{exp}(j2\pi f_ct)\...
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How does analog television chroma signal work with QAM and vestigial sideband?
In NTSC analog television (presumably PAL is similar) the chroma (color) signal is included through a subcarrier which is QAM modulated. This particular QAM modulation is a bit unusual in that besides ...
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How is IQ-modulation done on the digital side rather than the analog side?
The original way of doing In-phase Quadrature (IQ) modulation is by modulating and mixing on the analog side. I have read that as the digital processing have gotten better, the modulation and mixing ...
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Efficient Implementation of Digital Upconversion
I have an application where I have a pulse shaped QAM signal, at 2 samples per symbol. I need to take the I/Q samples and perform quadrature upconversion so that they can be output on a DAC that's ...
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I/Q Imbalance Correction using S.W. Ellingson Algorithm
Correcting I/Q phase and amplitude imbalance using S.W. Ellingson method.
https://www.faculty.ece.vt.edu/swe/argus/iqbal.pdf -- S.W. Ellingson Algorithm
When I try to use the set of equations to ...
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Sampling with an alternating phase offset
Suppose, I sample a signal $z=\mathrm{e}^{\mathrm{i}\omega t}$ alternatingly in $I=\mathrm{Re}(z(t))$ and $Q=\mathrm{Re}(\mathrm{e}^{\mathrm{i}\alpha}z(t))$. Thus my data array contains
$$\texttt{data ...
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Can complex envelope be writen in the form of quadrature components when it has symmetric spectrum?
I am reading a chapter on VCO noise in "Design of CMOS phase-locked loops from circuit level to architecture level by Behzad Razavi";I am confused when the upconverted noise is writen as $...
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Maximum NCO frequency and filter design for down-conversion of complex input signal
I am trying to perform digital down conversion by using the DDC from Matlab dsp toolbox. My question is that the bandwidth property is limited to Fs/2 and the filters created are real filters. If the ...
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Code Snippet to Convert ADC Samples to I/Q
I'd like to pull a narrowband signal out of ADC samples, where the ADC rate is much higher than the bandwidth/central frequency of the narrowband signal. I'd like to feed the narrowband signal into a ...
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I/Q sampling with just one ADC
Usually I/Q sampling is performed on two signals with a 90° phase shift using separate ADCs. Suppose I have only a single (fast) ADC available to perform I/Q sampling, which approaches do exist? Is ...
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Find which signal was transferred in 32QAM
I've been assigned to solve a problem for 32QAM signals. The thing is, there are little to none sources in my native language to get any decent information on the topic.
The problem is (in its ...
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Where does the imaginary part of a singnal come from? [duplicate]
So I recently watched this lovely overview of DSP/SDR explaining how demodulation of AM and FM becomes trivial by turning a signal into a complex number. (AM being the magnitude of the number and FM ...
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Recover frequencies from IQ samples
I have a set of IQ data. From those data I'm trying to get the amplitudes and the frequencies of my signal as I then want to plot them vs. time.
I am able to obtain the amplitudes by squaring both ...
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Fast phase calculation
I need to detect the PSK modulation posted on my previous post (phase difference detection) with 8 to 16 phase constellations (depending on selected baud rate) over a max $60^\circ$ PSK phase range. ...
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Why is In-phase Quadrature sampling not used to record and store digital audio?
I/Q is a standard method to sample radio frequency and its use is even seen in some non radio signals like sonar. But it seems that it is not used to sample acoustic frequencies.
What property of ...
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Obtain I/Q Components from a Real Signal On the Fly - Hilbert Transform or Digital Downconversion?
I'm planning to build a data acquisition system for a software-defined radio receiver. Basically, it just uses an ADC which samples an analog signal and send the signal to a processor. And then a ...
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I Q sampling and baseband version of analytic signal
Is it correct to say that if we have a radio signal $s(t)$ centered around the angular frequency of $\omega$ as $\omega\pm\omega_B/2$ (where $\omega_B$ is the bandwidth of the signal) and the ...
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Complex time domain signals and QAM
Is there an inherent connection between complex time domain signals and QAM?
Given a complex time-domain signal is it always implied that this is a QAM-demodulated form of a real time domain signal?
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IQ signal FM descrimination using phase derivative
I'm trying to demodulate an FM signal recorded as IQ samples from RTL-SDR at 2.4Msps with RTL-SDR centered on an FM station's frequency.
So the input signal is 8 bit IQ baseband at 2.4MSps.
The data ...
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340
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Converting a discrete real time domain to a discrete complex time domain signal
To test my understanding of amplitude modulation in the frequency domain I'm trying to replicate the center frequency with 2 side-bands in an Octave plot with the following code
...
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Intuitive meaning of complex time domain signal representation (quadrature sampling)
I saw What is the meaning of imaginary values in the time domain?.
My question is about I Q samples as recorded from an SDR receiver (e.g. RTL-SDR).
My understanding is that we can call these I Q ...
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Question about quadrature signals
My question is related to this article: https://www.dsprelated.com/showarticle/192.php
I think I understand mostly everything until this sentence:
"The directions in which the impulses are pointing ...
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Understanding FFT size in OFDM modulation
I know that the FFT size is the the number of subcarriers OFDM system have. But I also know that the FFT has to be $ 2^N $ big (in order to process N samples from time domain to frequency domain).
...
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QAM constellation coder - transmitting a file
The file with size 6 MB is transmitted in 100 seconds using a constellation coder QAM with a constellation of 6 bit/symbol
$ { M = 10^6, B = 8} $
Tasks:
1. What is the signal bandwidth if the band ...
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In case of using a Doppler radar, do we have to use IQ demodulation to find the direction of a target?
I want to know the way to find the velocity of a target by using a doppler radar.
I read some paper about it,
In summary,
send rf signal to a target
receive the reflected signal from the target.
...
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Quadrature component - condition on equivalent lowpass signal
I have a question regarding the equivalent lowpass signal $x_{LP}$ of a bandpass signal $x(t)$ and the quadrature component.
I'd like to find a condition on $x_{LP}(t)$ and $X_{LP}(f)$ such that the ...
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Why complex signal has no imaginary spectrum
I am learning about complex sampling.
I am confused why $~e^{ j 2\pi f~ n}~$ has only a real spectrum. I would have thought the $j ~\sin(2 \pi f n)$ would produce a single spike in imaginary spectrum ...
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How to correct a QAM time delay
How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system?
My only idea is to compensate the delay with an advance but this is impossible since you ...
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Question about QAM
I'm trying to understand QAM transmission and I'm struggling to understand this sentence, 'The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to ...
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I have the scatter plots for a Hamm and Tukey(0.25) windowed data. The complex data plotted from Hamm windowed forms a pattern, why?
The Hamm windowed complex data forms some sort of a quantized pattern whereas in the same code if tukeywin(0.25) is applied normal noise is observed. Any idea why ?
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How to generate IQ component for transmitting 2FSK
I am trying to generate IQ components for 2FSK modulation.
I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
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Contradiction between complex baseband and real-valued baseband
Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
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How to test I/Q modulation with only one branch (I or Q)?
Given is a direct-conversion I/Q up- and downconverter system. Receiver and transmitter share the same (10MHz) reference and hence the LO frequency is identical and there is an (unknown) phase ...
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Quadrature demodulation, homodyne detection, lock-in detection - what's the difference?
Quadrature demodulation
Homodyne detection
Lock-in detection
What is the difference between these terms? Are they all synonomous? In my mind they kind of are, so I'm never sure which to use.
I ...
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What techniques are available for correcting constellation rotation due to phase ambiguity?
In order for a receiver to recover a baseband signal, it needs a carrier signal equivalent to that used by the transmitter for upconverting the original baseband signal. Unless pilot tones are used, a ...
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