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Questions tagged [frequency-modulation]

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Implementing signal processing techniques for consistent RSSI signal reception

I've tried to optimize the LoRa setup using Arduino IDE libraries to ensure accurate or acceptable RSSI measurements and for distance estimation between multiple nodes and a master in an outdoor ...
Ausen's user avatar
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NBFM and WBFM power spectral density

The power density of a general FM modulated signal(with modulation index close to 1) looks like this: By picking out the carrier frequency we can make the FM signal narrowband or wideband.Now ...
Root Groves's user avatar
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Why is modulation index called modulation index?

The phase of CPFSK is defined as in this, page 4 $$\phi(t;I) = \theta_n + 2 \pi h I_n q(t-nT)$$ for $nT \leq t \leq (n+1)T$, with $h$ defined $h=2 f_d T$ called modulation index. What does it mean by &...
Cath Maillon's user avatar
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Does MSK modulation maintain continous phase after spectrum spread?

I need to check if MSK modulation keeps the phase continuous after DS spectrum spread. My thinking is that since we're expanding the bandwidth, it likely involves abrupt frequency changes so it won't ...
Ketterle's user avatar
2 votes
2 answers
393 views

What does really Time Chirp contribute to Range and Doppler estimation in FMCW radar signal?

As I started researching FMCW radar signals, I discovered a popular reference code for FMCW simulation in Github. One of the most important things that I still don't understand is the parameters ...
Rayzain's user avatar
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USRP X310 not receiving anything but noise

I have been trying to receive different types of signals using a USRP X310 but all I can receive is noise. I tried different types of antennas and designed many different kinds of blocks but I get ...
Ahsan Yousaf's user avatar
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What is wrong with this FM synth implementation?

I'm trying to get an FM synth to work, the synth uses wavetable oscillators, I am adapting the formula for FM synthesis: $$ FM(t) = A \sin(\omega t + B \sin(\omega_m t))dt $$ To use wavetable ...
TiagoLr's user avatar
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1 answer
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Why is my FM synth getting out of phase?

I'm trying to create a software FM synth following the formula for frequency modulation: $$ y(t) = A \cdot f_c(t + I \cdot f_m(t)) $$ Where $A$ is amplitude, $f_c$ the carrier function, $f_m$ is the ...
TiagoLr's user avatar
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CFO Estimation in LoRa Chirp Signal (Preamble part)

I am trying to estimate CFO in LoRa chirp signal (preamble part). I have seen the discussion about CFO on this forum but it is mainly related to CFO estimation in OFDM. I want to estimate the CFO in a ...
Mogambo0001's user avatar
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How to Eliminate Clicking Sounds in WAV File Generated from NFM Demodulation using FFTW?

I am working on a Digital Signal Processing (DSP) project where I am processing signals received from an SDR (Software Defined Radio) device. I am using the SoapySDR library to interface with the SDR ...
SignalWhisperer's user avatar
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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 ...
Thanos's user avatar
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1 answer
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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 ...
Kunal Vaidya's user avatar
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1 answer
248 views

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 ...
Jim's user avatar
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3 answers
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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,...
pej's user avatar
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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 ...
Grag's user avatar
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2 answers
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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 ...
Volpina's user avatar
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4 votes
1 answer
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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 ...
LuckyPants's user avatar
3 votes
1 answer
170 views

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 ...
cooldanietje's user avatar
2 votes
0 answers
259 views

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 ...
Jordan's user avatar
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1 answer
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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(\...
unique's user avatar
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1 answer
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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: ...
Denis Kotov's user avatar
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1 answer
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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 ...
Pratheek's user avatar
1 vote
2 answers
798 views

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: <...
JonPC's user avatar
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0 answers
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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 ...
Moses Kim's user avatar
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5 votes
1 answer
1k views

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, $f_c$ ...
Moses Kim's user avatar
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1 vote
1 answer
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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 + ...
Chris Akridge's user avatar
0 votes
1 answer
238 views

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 ...
Moses Kim's user avatar
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1 vote
0 answers
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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 ...
Jacob's user avatar
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1 vote
1 answer
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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 ...
P. Egli's user avatar
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1 answer
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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 ...
Nick Elias's user avatar
0 votes
2 answers
652 views

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 ...
Hubert S. Cumberdale's user avatar
2 votes
1 answer
69 views

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 ...
user avatar
0 votes
1 answer
43 views

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 ...
sudheer's user avatar
2 votes
1 answer
609 views

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 ...
Logan's user avatar
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0 answers
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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 ...
vg8open's user avatar
1 vote
1 answer
254 views

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 ...
average_discrete_math_enjoyer's user avatar
1 vote
0 answers
70 views

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 ...
user674907's user avatar
2 votes
2 answers
923 views

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 ...
Nick Elias's user avatar
0 votes
1 answer
108 views

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. ...
Vrisk's user avatar
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1 vote
1 answer
478 views

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 ...
halomi's user avatar
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1 vote
2 answers
507 views

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 ...
halomi's user avatar
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0 votes
0 answers
345 views

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 ...
Robin Hellmers's user avatar
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1 answer
446 views

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) ...
Mathpdegeek497's user avatar
1 vote
0 answers
349 views

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 ...
Jonathan_the_seagull's user avatar
1 vote
0 answers
737 views

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 ...
boatradionerd's user avatar
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1 answer
177 views

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 ...
user3141592's user avatar
1 vote
1 answer
1k views

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?
Marcin Puchlik's user avatar
1 vote
1 answer
732 views

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: ...
yarin Cohen's user avatar
0 votes
3 answers
7k views

Python- FM Modulation

I am trying to Frequency modulate a sine signal using Python. I have written the following code that should do it: ...
yarin Cohen's user avatar
0 votes
2 answers
190 views

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 ...
Patrick's user avatar
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