Questions tagged [frequency-modulation]

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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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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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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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Range-Azimuth Heat map (FFT)

I have a question regarding performing a 2D complex FFT on a 2D array of frequency information in one dimension and azimuthal change in degrees in the other dimension. That is, I ran a test with an ...
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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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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, ...
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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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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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2 answers
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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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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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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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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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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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28 votes
6 answers
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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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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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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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1 answer
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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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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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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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1 answer
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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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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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-1 votes
1 answer
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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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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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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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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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2 answers
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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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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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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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7 votes
3 answers
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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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