Questions tagged [frequency-modulation]

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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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1answer
28 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 ...
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1answer
52 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?
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82 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: ...
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118 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: ...
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2answers
27 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 ...
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1answer
52 views

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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6 views

Find the total amount of frequency multiplication needed for an Armstrong indirect FM modulator, when frequency deviation is adjustable in a range

I am currently practicing for my college exams and in this question, they are asking us to find the total multiplication needed in the system. But I am stuck because I have no idea of how to make use ...
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1answer
24 views

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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113 views

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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23 views

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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1answer
38 views

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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43 views

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, ...
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66 views

Frequency modulation: which algorithm for discrete signals (Java, Swift, etc.)

I'm writing an audio app in Swift - and one task consists in frequency modulation of a given signal (microphone input or sound file) - thus I'm iterating through all frames of a buffer like ...
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47 views

FM modulation - recovering bits

I'm trying to complete one task: Download some FM modulated signals from page http://www.w1hkj.com/modes/index.htm. Calculate their spectrograms, i.e. short-time Fourier transform. Observe different ...
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2answers
342 views

Spectrum of FM signal?

If a carrier ($f_c$) is FM modulated by a single sine wave ($f_m$), its spectrum is composed of frequencies at $f_c + kf_m$ ($k \in \mathbb{Z}$) whose amplitudes are weighted by $J_n(\beta)$, the $k$-...
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48 views

Convert old computer cassette signal into binary

Completely new to this but keen to learn :) I have an old BBC Micro computer cassette which I've recorded into unsigned 8-bit pcm wav file format. The file comprises tracks separated by virtual ...
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148 views

Wideband FM bandwidth estimation

In the book Modern Digital and Analog Communication Systems by B. P Lathi, there is a section for the estimation of WBFM bandwidth. First, the staircase approximation of $m(t)$ is constructed by the ...
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2answers
139 views

Power of an angle-modulated wave

Let $$\phi(t) = A\cos(\omega_c t + km(t)) \tag{1}$$ be an angle-modulated wave(FM or PM). What's the power of $\phi(t)$? Intuitively, it seems that the answer is $$P = \frac{A^2}{2} \tag{2}$$ since ...
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What does the variable $\tau$ mean in frequency modulation?

Frequency modulation formula: $$ x_{FM}(t) = A_{c}\cos\left(2\pi f_{c} t+ 2\pi k_{f}\displaystyle\int_0^{t}m(\tau)d\tau+\phi_{0}\right) $$ Its change from $m(t)$ to $m(\tau)$. What is $\tau$? I wonder ...
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59 views

Non-coherent FSK and Orthogonality and square-law detectors

This is a basic figure that explains how Non-Coherent FSK actually works. The incoming signal $ r (t)=\sqrt{2 P}{Cos}(2 \pi t (\text{fc}+\text{fi})+\text{n(t)}$ where P denotes the signal power in ...
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Why can so little digital information be stored on a cassette tape?

I had heard that tape is still the best medium for storing large amounts of data. So I figured I can store a relatively large amount of data on a cassette tape. I was thinking of a little project to ...
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3answers
60 views

Can the intelligence message of an FM signal be cross-modulated to another center frequency due to non-linearities?

Can the intelligence message of an FM signal be cross-modulated to a a different frequency by non-linearities, but with the FM modulating message remaining (relatively) intact on the new frequency? ...
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56 views

Why does sampling chirp at peak frequency yield correct frequency response?

Followup; setting Fs = bandWidth in accepted answer's code yields the "correct" frequency response of an LFM chirp: constant magnitude, parabolic phase. ...
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1answer
28 views

Signal distortion under non-linear channel

The channel is given to have these characteristics, and its required to study the affect on Frequency Modulated signal and its demodulation. Since there are no sharp corners (like during clipping) ...
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44 views

Instantaneous frequency, PLLs, frequency mixing, cross-correlation and the cross-correlation matrix

This is as much a request for comment and critique as anything else. I am looking at tracking how a system perturbs an input that is a (real) sinoid of varying frequency. ...
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1answer
45 views

RF Downconversion using Heterodyne Principle

after a RF down-conversion using heterodyning principle, will there be an information loss? If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be ...
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1answer
294 views

How to demodulate PM modulation

I'm using a sin wave $s_{sc}(t) = d(t)\cos(\omega_{sc}t + \varphi_{sc})$ to modulate a carrier using phase modulation. I'm working on Matlab so I use the pmmod function to do so. It is not too ...
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124 views

DSP based FMCW radar

I have an SDR receiver I'm interested in making into a FMCW radar. The bandwidth is somewhat narrow as it only samples at 64 MSPS. There is a problem in that without a bunch of embedded programming ...
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1answer
428 views

How to generate WBFM from NBFM?

An FM signal is given by $$ s_{FM}(t) = A_c \cos [\omega_C t +k_f \int _{-\infty}^t m(\alpha)d \alpha] $$ Let $ \int _{-\infty}^t m(\alpha)d \alpha] = a(t) $ Therefore, $ s_{FM}(t) = A_c \cos [\...
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1answer
140 views

How to generate WBFM from NBFM

A narrowband FM is approximately given by: $ x(t)= A[\cos w_ct - k_f a(t)\sin w_ct] $ where $ a(t)= \int _{ -\infty } ^t m(\alpha) d\alpha$ How does frequency multiplying $x(t)$ by a desired ...
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73 views

What is the Fourier Transform of $\DeclareMathOperator{\rect}{rect} \rect(2Bt)\cos[{\omega}_Ct + k_fm(t_k)t] $?

What is the Fourier Transform of $\rect(2Bt)\cos[{\omega}_Ct + k_fm(t_k)t] $? I got the following as the solution: $$\DeclareMathOperator{\sinc}{sinc} \frac{1}{2} \frac{1}{2B} \sinc(\frac{\omega+{\...
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28 views

Doubt in Frequency Modulation code

While searching for something FM, I came across this code. I am not able to understand a particular line of code. I have written a comment against that line of code. ...
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2answers
231 views

Frequency modulation in MATLAB

I am trying to frequency modulate a cosine signal(for assignment). I have written the following code but not getting the required output. ...
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1answer
41 views

FM: Do rational ratios of carrier to modulator signals really produce harmonic spectra?

I've read that in FM, all rational ratios of the carrier frequency to the modulator frequency produce harmonic spectrum in the FM signal. Link to what I read. I don't understand why this is. If for ...
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1answer
187 views

Frequency response of FM modulation/demodulation chain with phase derivative demodulation

Frequency modulating a carrier by white noise and then demodulating the complex signal using discrete derivative of phase it appears that the discriminator is acting as a low-pass filter. How do I ...
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862 views

Why do we integrate the modulating function in FM?

I've been reading about FM and I keep coming to an expression, where the instantaneous phase $$\Theta=2\pi f_it+\phi\text, \tag1$$ where $$f_i=f_c+k_fm(t)\text,\tag2$$ ($f_c$ being the base carrier ...
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2answers
255 views

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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1answer
408 views

Demodulating wideband FM signal in Octave from recorded baseband IQ samples

Assuming I have a baseband recording of 8 bit IQ samples at 2.4MSps centered on an FM station is it correct to say that after low pass-filtering the complex signal to 240KHz, taking discrete ...
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1answer
88 views

Positive slope of BER with a greater frequency deviation?

I am trying to implement a frequency-modulated communication channel on MatLab. However, there is something I don't understand about the sensitivity of the frequency modulator (or the frequency ...
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1answer
568 views

Digital FM Demodulation

I have created a Common Lisp Library to receive samples of an FM signal from BladeRF1 SDR. I want to write a subroutine to implement FM demodulation. The input should be in the format of IQ data. ...
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1answer
283 views

Question about FMCW range-velocity plot

I am working on plotting range-velocity heatmap of the receiving FMCW signal. I actually have already plotted. However, I do not really understand the mapping relationship between Doppler FFT bin and ...
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154 views

Which equipment to use for testing performance of AM, FM, and DAB

I want to test the performance of AM, FM and DAB radio in RTL-SDR. I want to measure sensitivity, adjacent channel selectivity, cross-modulation/blocking, and third-order intermodulation to be some of ...
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1answer
288 views

Equation of wave in Linear frequency modulation?

We know that we have the following equation for wave. $$g(t)=A\cos(\omega t+\theta_0)=A\cos(2\pi ft+\theta_0)$$ The equation of frequency with respect to time will be: $$f(t)=\frac{Bt}{\tau}+f_c-\...
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44 views

Help in identifying low speed image transmission protocol over RF

In the seventies I worked for Muirhead on press fax machines that used to transmit pictures over radio and landline as I recall two FM systems were used a carrier 800 Hz modulated +- 150 Hz and 1900Hz ...
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25 views

Is there a software/application that shows the FM base stations nearby us?

I want to collect a list of FM base stations near me. I have found apps/software for finding LTE base station but found no success in finding an app for FM base station.
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1answer
167 views

Fourier transform of frequency division

I need a mathematical description of what happens to the spectrum of a signal when that signal is processed to divide its frequency. As an example, construct an input signal as the sum of two sine ...
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1answer
255 views

Frequency modulation audio synthesis: clicks/pops when changing modulator frequency dynamically

I'm very new to DSP and working on a FM VST. It's mostly up and running, or at least it generates FM-like sounds. I want to be able to change various parameters dynamically while audio is generated, ...
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579 views

Spectrum of WBFM signal for triangular message signal spectrum

We Know: Frequency Modulated signal is given by: $$s_{FM} (t)=A_{c} \sin \{ w_c t + 2 \pi k_f \int m(t) \, dt \}$$ Now, if $ \quad m(t)= A_m \cos(w_m t)$ , i.e, its spectrum $M(f)$: then, $$s_{FM} (t)...