Questions tagged [frequency-modulation]
The frequency-modulation tag has no usage guidance.
138
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I don't understand which signal I should use as a carrier in my excersise
$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals
$x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$,
where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$.
I must ...
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request pointers on beginner DSP board for making an EQ simulating hearing aid prescription with TV sound
I want to make an equalizer set to similar frequency cut-boost according to the results from the graph from hearing test, where an audiometrist will play tones of various frequencies at various ...
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How can I apply a phase shift to an LFM pulse?
I am modelling radar scenarios in python and am trying to make a model which retains phase information. To do so, I'm envisioning something which works like this:
Generate samples of an LFM waveform ...
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FMCW Radar - What's wrong with the transmitted signal model?
I am new to FMCW radar and trying to plot the transmit signal over time.
As you know, the transmitted signal is modelled as:
$$s(t) = cos(2\pi f_c t + \pi S^2),$$
where $S = BW/T_{chirp}$ is the slope,...
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Properly FM Demodulation & Display baseband FFT in QT using QTCustomPlots
I am having trouble trying to display the baseband signal because it looks incorrect.
How do I properly display the baseband signal? Should I be doing a float to complex transformation? Am I doing ...
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129
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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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Why can FM be used to encode a message, intuitively?
I am reading about FM.Suppose the message signal $m(t) = \frac{1}{2}cos(t)$ and the frequency of the carrier signal is twice the frequency of the message signal and its amplitude is 1.The resulting ...
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FFT on SDR FM Radio Signal
I recorded a simple FM signal using my SDR (centered at 100.3e6 hz and sample rate of 2.048e6 per second). Without any transformation, I ran an FFT on the signal and it showed a signal with some width ...
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Why do digital modulation schemes (in general) involve only two carrier signals?
In my digital communication, class we have covered the various modulation schemes, namely QAM and its derivatives (B(A/P)SK, PAM and (Q/M)PSK) as well as BFSK. These two schemes have one or at most ...
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Ambiguity function information
For a course that i'm taking im asked a question about the ambiguity function of a FMCW radar. However i have not found a good source for reading about this so don't quite understand it.
I get given ...
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FSK: Selecting center frequencies and Carson's Rule
I'm implementing 2FSK and 4FSK modulation schemes for an experimental system. I'm using GNURadio, although that shouldn't affect the question.
I'm trying to figure out how the center frequency should ...
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Why don't we need frequency and phase correction in AM and FM?
As far as I understand, double sideband AM with carrier and FM can be demodulated via SDR (Software Defined Radio) without frequency or phase correction. For AM, received signal is
$$r(t) = A(t)\cos(\...
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python how to demodulate iq fm signal that was moved to 0 frequency
I am struggling with implementing FM demodulation for IQ samples that has 0 center frequency from RTL-SDR ...
I have found the following algorithm for FM demodulation, see FM demodulation:
...
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170
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Frequency shift after signal passing through a band pass filter in Python
I'm trying to simulate frequency demodulation in Python. As a part of this, I'm implementing a band-pass filter with cutoff frequencies at $f_c-2f_m$ and $f_c+2f_m$.
There is frequency shift in the ...
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IQ Constelation Diagram of FSK signal
I'm want to generate the IQ components of a FSK signal using numpy and then try to demodulate the resulting IQ samples by looking at the derivative of its phase in time.
This is the script I have:
<...
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Deriving the IF phase equation of FMCW
My understanding of the FMCW was limited to one chirp and was mostly focused on frequency analysis. (Mostly built upon this answer)
I wanted to expand my understanding to multiple chirps and was ...
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Range-Doppler Coupling in FMCW
I did some derivation of the IF signal of the FMCW using sawtooth LFM.
A chirp with sawtooth LFM is expressed like below
$$x_T (t)=\cos\left(2\pi f_c t + \frac{\pi}{T}B (t-mT)^2 \right)$$
Where, $f_c$ ...
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Why is a multiplexed FM signal broadcasting silence so... spiky?
I'm trying to understand how American FM multiplexing works. As I understand it, your average FM signal can be made out of:
The mono "sum" channel from 30 Hz to 15 kHz, made out of left + ...
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116
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FMCW chirp data acquisition
I am trying to understand the full mathematics behind FMCW. Using linear-frequency chirp $x(t)$ that has center frequency $f_c$, bandwidth $\Delta f$, duration $T_r$, and amplitude $A$, the ...
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numerical time differentiation in GNURadio
I'm hoping to put together a cheap modulation monitor for wideband FM radio using an rtl sdr usb, on the FCC website, it's listed that the modulation percentage for an FM station is the actual ...
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Finding the carrier frequency of a NBFM signal
My goal is to cross-correlate FM signals received at multiple locations using RTL-SDR (and perhaps other SDR receivers) and for that, they should be aligned in frequency. The cross-correlation will be ...
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Instantaneous frequency vs time for a piecewise signal
I sample a signal that consists of a train of pulses which are amplitude and frequency modulated. I would like to generate a plot that is instantaneous frequency vs time. I compute the Hilbert ...
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How to demodulate FM I/Q output from SDR#
Using SDR#, I saved the baseband I+jQ signal centered about a commercial FM station to a *.wav file. I want to write python code to demodulate this signal. I know that SDR# can read in that file and ...
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338
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How to recover symbols from a 4-FSK signal received over the air?
I have an RTL-SDR dongle which is tuned to a carrier frequency in my area which corresponds to a P25 radio channel (506.7375MHz).
Using MATLAB's SDRRTLReceiver function, I sample the signal at 240KHz ...
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FMCW Transmit Signal and Fly-back Effect
I am studying a thesis about nonlinearities in the transmit signal and it mentions the following:
The first 2,500 samples, which correspond to the Tmax of each of each
sweep period and are affected ...
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Does frequency modulation by direct method cause any phase modulation?
Phase modulation causes instantaneous frequency to vary according to modulating signal.
In the same way does Frequency modulation by direct method causes any phase variation in proportion to ...
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416
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Fractional Frequency Shifting a Discrete Signal in the Frequency Domain
In our current hardware-based signal processing pipeline, we have a time-domain signal $x[n]$ that we want to frequency shift by $f_0$. To do this, we multiply the signal by a complex exponential in ...
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390
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Mono FM radio demodulation
I am trying to demodulate an IQ file containing a sample of a FM radio signal using two methods. First, I tried reading the whole file and demodulate all data at the same time. Second, I tried ...
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Power of signal in specific frequency in FM and AM modulation
My professor gave us the following problem:
Given a sinusoidal signal with $f_m = 1KHz$ which is put into an AM
and FM modulation find the modulation index of FM and AM if you know
that (amongst ...
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What is the difference between sending pulses and modulating waves?
If you look for amplitude, frequency, phase modulation, you typically get some picture saying you have a wave and you modulate the corresponding parameter (amplitude, frequency, phase). On the other ...
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I'm missing something when it comes to understanding FM
I understand why FM is preferred for music: noise is mostly amplitude modulated, FM yields much higher fidelity. I also understand why commercial FM signals have a much larger bandwidth than ...
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Using SSB modulation to frequnecy shift an arbitary signal downwards
I've managed to use SSB digitally to create frequency envelopes such that I can increase frequencies at any arbitrary rate given by my envelop. But I am unable to manage a downward frequency shift. ...
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I am working on chirp signal generation using DDS in verilog . To generate the chirp signal do I need to change the limit of the 8 bit counter?
I want to generate linear frequency modulated (LFM) waveform or a chirp signal using DDS in verilog. I am not using DDS IP Core. I have created DDS module using 8-bit rate counter, a 12-bit address ...
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Can someone help me with chirp signal generation using direct digital synthesizer(DDS) in verilog?
I want to generate linear frequency modulated (LFM) waveform or a chirp signal using DDS in verilog. I am not using DDS IP Core. I have created DDS module using 8-bit rate counter, a 12-bit address ...
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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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Phasor diagram of Phase modulated signal
While studying the phasor diagrams of Amplitude modulation and Frequency modulation, I am stuck at a problem involving the phasor diagram of an angle modulated signal whose equation is given by $$s(t) ...
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FM and PM waves
I have to find the FM and PM waves corresponding to this sawtooth signal:
I have found out the PM wave as:
I am getting the FM wave as this :
I have plotted this using Python. Can anyone please ...
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Digital Selective Calling (DSC) Decoder in GNU Radio
I’m attempting to develop a GNU Radio FSK decoder for Digital Selective Calling on marine VHF but I seem to be stuck. I got my hands on a Standard Horizon handheld marine VHF unit with DSC capability ...
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114
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MSK receiver for ultra-low SNR
I am designing a low-rate DSSS communication system (~1ms chip period, Spreading Factor 128/256 bits long) for using at ultra low SNR scenarios (~0dB SNR).
Due to the problems related to clock ...
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Difference between FFSK and FSK modulation schemes
Can somebody explain to me what is the difference between FFSK (Fast Frequency Shift Keying) and FSK (Frequency Shift Keying) modulation schemes?
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How to Frequency Modulate an Audio Signal
I've started to learn about FM and I followed this guide to FM a sine wave.
I have managed to do it and here is the result:
And the code:
...
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Python- FM Modulation
I am trying to Frequency modulate a sine signal using Python. I have written the following code that should do it:
...
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Real-time FM demod results in clicking and strangely-shaped output
hardware engineer here dipping his toes into software DSP and running into some issues.
I'm attempting to demodulate in realtime a simple narrowband FM signal with samples from an RTL-SDR, and play ...
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How to Modulate down a hidden message after filtering base signal from audio file
I have an audio file that is 6 seconds long. The file has a message hidden into it in the ultra high frequency range. I plot the Mel Spectrogram with a sample rate of 44100 and use a high-pass filter ...
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Transmitting an approximate CW with an FM modulator
Imagine we had an FM modulator with carrier frecuency $f_c$. My doubt is about the optimal approach to use it for transmitting a tone (CW) of a frequency $f_c+\Delta f$.
Let $x(t)$ a and $y(t)$ be the ...
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What is the advantage of using a Stepped Frequency waveform over FMCW?
What is the advantage of using a Stepped Frequency Waveform instead of a traditional linear FMCW ?
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Voltage Controlled Oscillator for An Arbitrary Sinusoid
I have a time-varying signal:
$$ y(t) = g(t) + a(t) \sin(2 \pi f_m t) $$
$g(t)$ and $a(t)$ are varying with time.. I have both of them as 2D arrays of [time value]
I need to perform VCO for $y(t)$ in ...
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I can't understand why there is a phase shift in phase modulation of a sawtooth wave
This is regarding question 5.1-2 (see picture attached) from Modern digital and analog communications, Lathi & Zhi Ding (2010).
I do not understand what the behavior should be at the ...
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Pointers for digital FM synthesis
I am working on a digital synthesis project, in python and c currently. I have made a Sine and Saw wave generator and have now been working on FM between the two wave types. I have successfully made ...
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Advice on generating stable FMCW waveform
I am trying to derive parameters for a triangular FMCW waveform such that the phase of the signal has consistency from one period to the next. Perhaps this is arbitrary and feel free to tell me so, ...
