# Tag Info

Accepted

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

Because each step in the processing chain is linear we consider a case with only noise and no coherent signal. Denote the noise $\xi(t)$. The $I$ and $Q$ signals are \begin{align}\ I(t) &= \xi(t) \...
• 1,016

### FSK and IQ modulation

What is the advantage of performing the FSK using IQ modulation? You only need one RF oscillator operating at a single frequency, instead of having 2 (or more in the case of M-ary FSK) oscillators ...

### How to "draw" the function/wave to send symbols using QAM?

The baseband QAM signal is complex, and the only way to draw it is by doing two drawings, one for the in-phase (real) component, and one for the quadrature (imaginary) component. The passband QAM ...
• 13.8k

### Why do SDR receivers emit I/Q samples?

The SDR (or any general digital signal processing system) takes the received RF signal, and downconverts it from the carrier frequency to the baseband. Now, the real bandpass signal from the antenna ...
• 6,068
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### Quadrature modulation for FM and AM

Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and receive radio signals. This question is ill-defined – a signal ...
• 26.3k

### Sending complex signal over a single wire

Note that signals sent over wires (and over the air, and over any medium) are always real. What quadrature means is that, on a passband channel (wired or otherwise), you can transmit two signals at ...
• 13.8k

### FSK and IQ modulation

There are many ways of demodulating the FSK signal Indeed! What is the advantage of performing the FSK using IQ modulation? Depends. Generally, IQ is the only shape you have your signal in, so ...
• 26.3k
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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 ...
• 18.9k

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 ...
• 13.8k
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### How to reconstruct RF signal using IQ data

The RF signal $r(t)$ is obtained from the complex baseband (IQ) signal $s(t)=x(t)+jy(t)$ in the following way: $$r(t)=\text{Re}\{s(t)e^{j\omega_0t}\}\tag{1}$$ where $\omega_0$ is the carrier ...
• 80.2k
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### Difference between these two digital down conversion methods

As you already know, the two methods are theoretically identical if there's no noise. If there is out-of-band noise then the low pass filters in method A will further suppress the out-of-band noise, ...
• 80.2k

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

i will call the bandpass signal: \begin{align} y(t) &= \Re \Big\{ (x(t) + j\hat{x}(t)) \, e^{j \omega_0 t} \Big\} \\ \\ &= x(t) \cos(\omega_0 t) - \hat{x}(t) \sin(\omega_0 t) \\ \...

### Quadrature demodulation, homodyne detection, lock-in detection - what's the difference?

They are essentially the same but may have key differences varying across implementation. The process is identical in terms of multiplying a signal by a sine wave at the center frequency of the signal ...
• 37.1k

### How to test I/Q modulation with only one branch (I or Q)?

The FSW is superheterodyne. This means that it will not have a DC offset or I/Q imbalance, but the IF path will appear as an asymmetrical lowpass (because it is really a shifted bandpass), which is ...
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### Quadrature component - condition on equivalent lowpass signal

Your idea with the Hilbert transform doesn't work. The only signal (apart from $x(t)=0$) for which the Hilbert transform is zero, is a constant signal. A band pass signal $x(t)$ can be written in ...
• 80.2k
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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?

Radar designer here: It sounds like you’re talking about pulse-Doppler (PD) radar systems. For PD radars, the process is essentially as you described: Generate a waveform (typically at IF) and then ...
Accepted

• 37.1k
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### What is the advantage of measuring IQ data non-digitally?

IQ demodulation is normally done with the "I" component being sampled at a rate that is at or near (including below) the carrier frequency of the signal, or the center of the band of interest. Since ...
• 34k