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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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2answers
67 views

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 ...
2
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1answer
36 views

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 ...
3
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1answer
109 views

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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0answers
28 views

Modulation Index in Case of Quadrature Modulation (IQ-modulation)

It says that in case of quadrature modulation, the modulation index can be maintained at exactly 0.5 without any settings or adjustments. I don't get it why. What is it which is making it sure that ...
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1answer
35 views

Detecting I/Q imbalance

Are there any methods of detecting, measuring, and/or estimating I/Q imbalance (from, say, an upstream quadrature mixer and/or ADC), without using or having a controlled test signal (other than ...
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1answer
53 views

Modeling channel response as complex vs splitting I and Q

If I have a communications channel where a digital QAM signal is transmitted, I can either model the channel's impulse response as a complex $h(t)$, or as 2 separate impulse responses $p(t)$ and $q(t)$...
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0answers
85 views

Removing I/Q phase rotation

What is the most reliable and agnostic way to correct for a phase rotation of I/Q downconversion - without time alignment of the signal and support different lengths of transmitted and received data? ...
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1answer
155 views

How to eliminate negative frequencies from IQ signal

I have a 192kHz IQ signal from an RF receiver, and i'm trying to remove signals in the negative (or positive) frequency spectrum. I see that the negative frequency signals are -90 degrees phase ...
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1answer
145 views

Are IQ-samples independent from the carrier frequency?

Since i am not sure if i have understood IQ samples correctly, i want to ask the following question: If i look at inphase and quadrature in an IQ diagramme, the length of the arrow describes the ...
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1answer
550 views

In-Phase and Quadrature components of low-pass equivalent of a band-pass signal?

I was wondering what is the physical meaning of IN-PHASE and QUADRATURE components? In the context of low-pass equivalent of band-pass signals. Any help is appreciated!
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4answers
247 views

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

I've spent many hours reading and doing research about this. I don't attend any university classes or any type of classes that may approach such a topic. I am trying to learn this by my own without ...
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3answers
245 views

Sending complex signal over a single wire

The G.hn protocol uses OFDM to transmit data. And it sounds like they are doing it on a single wire. OFDM symbols are a complex number with I and Q components. How are they able to send two separate ...
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1answer
210 views

Recover IQ samples from signal

I have a data acquisition device that provides me with an array of integers that represents a modulated signal (let's say QAM16). I would like to recover the I and Q samples from the raw time-domain ...
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0answers
149 views

Complex bandpass filter giving quadrature signal

I have found a technique detailed on page 34 & 35 of this thesis. In this, the author states a complex bandpass filter can be derived by first making a prototype real valued IIR filter, then ...
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1answer
83 views

Why is no phase information lost when a received signal goes through a mixer?

I'm sorry if the question is too philosophical or makes no sense, but I need to be able to explain why it doesn't make sense. When we take the in-phase and quadrature-phase base-band components of an ...
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1answer
812 views

How to “draw” the function/wave to send symbols using QAM?

Say you have the following 8QAM constellation diagram: Say, you want to send the sequence: 001 110 101 000 001 How would you draw the function/wave containing the symbols? My problem in ...
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2answers
79 views

How do you compute for fc and t in modulating an I and Q component

I know that in a $2^b$-ary QAM system you need to modulate the $I$ and $Q$ components through the mixer and are separated by 90° through a local oscillator (by applying a $\cos$ and $\sin$). By ...
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2answers
475 views

IQ FM Demodulation of Wow and Flutter Signal in Software

Background: I have a recording device that exhibits Wow and Flutter, or periodic frequency deviation. I use this device to record a calibrated 3.15kHz test tone from a tape film to generate a .wav ...
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1answer
351 views

Maximum Throughput of QAM system

Consider a QAM system designed to transmit over a bandwidth of $3 \ \mathrm{kHz}$. The channel's power constraint imposes a maximum $\mathrm{SNR}$ of $30 \ \mathrm{dB}$. The system can tolerate a ...
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1answer
157 views

QAM-spectrum with uneven real & non-odd imaginary part

Despite the signal being real, as is seen in the last line of the first picture: , the exemplary spectrum of the signal shows neither an even real nor an odd imaginary part: But from my theorems I ...
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2answers
911 views

Why do SDR receivers emit I/Q samples?

To my understanding hardware receivers for software-defined radio applications basically take the input signal, mix it with the tuning frequency to remove the carrier frequency and then sample the ...
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2answers
295 views

What type of information can be contained in I/Q (quadrature) data?

I am taking in regards to, for example, the signals captured using a measuring instrument such as a spectrum analyzer. Basically would the I/Q data store all the parameters that my analyzer can ...
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2answers
3k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
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2answers
1k views

Quadrature modulation for FM and AM

This might be a naïve question, are these correct statements? Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and ...
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2answers
2k views

How to reconstruct RF signal using IQ data

I have a complex IQ signal: $s = X + Yi$. I know my original $f_0$ was $5\textrm{ MHz}$. I can calculate the magnitude/amplitude of $s$: $A = \sqrt{X^2 + Y^2}$ and phase, $\phi = \arctan\left(\frac ...
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1answer
596 views

What is the advantage of measuring IQ data non-digitally?

So I know In-phase and Quadrature (IQ) data can be used to analyze changes in both phase and amplitude of the signal. I also know that if I know the I component of the signal (which I could get by ...
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1answer
482 views

Generating QPSK Constellation Diagram

I was wondering how a diagram like this is generated. I am generating a QPSK signal using MATLAB by taking a cos and sin wave, multiplying each one by either 1 or -1 and adding them together to form ...
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2answers
533 views

Play IQ data in the soundcard

I have short-wave digital receiver that send RP packets with IQ components over network depend of the RF frequency and passband. I need to work with the telephone passband (0.3 - 3.4 kHz). The task is:...
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2answers
380 views

Root raised cosine pulse shaping peak value

I am using a FIR filter to generate Root Raised Cosine pulse for an IQ modulator. How can I predict the peak value at the output, depending on the roll-off factor of the pulse ? Knowing that : FIR ...
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3answers
1k views

IQ imbalance amplitude

I have to fix the amplitude of measured IQ receiver data. According to my information about the data, I can estimate that one signal needs to be corrected to the other in amplitude. The phase offset/...
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0answers
1k views

Doing analysis using IQ demodulation in Python

I'm trying to doing an analysis using IQ demodulation. I'm doing this by taking a noisy signal which has a desired signal in it. The desired signal has a frequency that is almost stable, which I'm ...
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1answer
155 views

Addition of two signals in polar coordinates

There is quadrature detector which receive radio signal and return its amplitude and instantaneous phase after performing hilbert transformation and transferring the signal to zero frequency. The main ...
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2answers
219 views

Reconstruction of BandPass Signal from Complex Envelope

From what little I've been able to gather, the complex envelope preserves all information required for the reconstruction of the original signal and that it basically sends a low pass version of a ...
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2answers
197 views

Quadrature modulation

I have a question: What is the difference between $ I \cos(t) - Q \sin(t) $ and $ I \cos(t) + Q \sin(t) $ except that they are phase shifted 90 degrees ? On the internet I can find both ...
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2answers
1k views

Difference between these two digital down conversion methods

I can think of two possible methods of digital down conversion. One seems superior to the the other for most cases, but I'd like to get some DSP experts' comments on the practical differences between ...
5
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1answer
1k views

What is the connection between analog signal to noise ratio and signal to noise ratio in the IQ plane in a quadrature demodulation system?

We would like to compute the quantitative relation between analog noise near the LO frequency and the statistics of points found in the IQ plane after IQ demodulation. In order to completely ...
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1answer
82 views

Spectral density of signal written as quadratures

Suppose I have a real-valued random signal $f(t)$ written as $$f(t) = I(t)\cos(\Omega t) - Q(t)\sin(\Omega t)\, .$$ What is the relationship between the spectral densities of $I$ and $Q$ and the ...
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0answers
539 views

IQ imbalance on quadrature signal

Hi I am attempting to develop a reasonable IQ balance mechanism for a quadrature signal coming from a software defined radio.I can balance out the amplitude and phase differences at one frequency ...
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1answer
78 views

Quadrature subsampling result not as expected

Let's suppose I have an ADC running at 81.824MHz. I am quadrature subsampling a signal that is at 143.5MHz using a sampling rate of 81.824MHz/4 = 20.456MHz = Fs. I expect the signal to appear at ...
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1answer
1k views

Splitting a Complex FIR Filter into Real Filters

I'm working on a software defined radio project on a PIC32 MCU. I'm using a CMX 973 quadrature frontend to provide I and Q. I'm independently low passing I and Q with carefully matched analog filters ...
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1answer
434 views

Software defined radio panadapter

I am trying to make a panadapter for a software defined radio and I am a little bit stuck and hope someone can help me. I have an I Q signal from my radio. (Actually I am using an IQ wav file from ...
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0answers
169 views

How to get the quaternionic analytic signal of a image?

The 2D discrete image signal's quaternionic fourier transform can be described as F(u,v), and its 2D analytic signal often be described as: $$ F_q(u,v) = (1 + \mbox{sgn}(u))(1 + \mbox{sgn}(v)) F(u,v) ...
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0answers
290 views

IIR biquad coefficients for negative frequencies in IQ data?

Assume I have a (single real float channel) biquad IIR filter implemented in C, and some coefficients for a bandpass filter (right out of RBJ's cookbook). If I convert the input, output, data path, ...
2
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2answers
538 views

How do you alter the phase relationship between I and Q in a quadrature signal?

I am collection a quadrature signal from a radio. The I and Q signals go through a sound card at a sample rate of 192000, and then a FFT is performed on the signals. Due to various reasons, the ...
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1answer
9k views

What exactly is a complex envelope?

I have seen this be mentioned a couple of times in some books I read, so I want to make sure. Is the complex envelope simply the summation of the real and quadrature components of a signal, whereby ...