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Questions tagged [frequency-modulation]

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1answer
73 views

How is frequency related to data rate?

How does (if it does) frequency affect/relates to Data Rate. Why for example using the same modulation, LoRa (in the physical layer), you get somewhere around 250kbps at 2.4Ghz and only 20kbps at ...
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1answer
84 views

FM synthesis algorithm is not very efficient

I have very little knowledge of DSP, I'm trying to implement an FM synthesis algorithm in code / software. So far I've successfully implemented a FM algorithm using the following: ...
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0answers
52 views

Best Way to Extract Frequency from Signal [closed]

I want to send signal that compound from 16 different frequency over GSM. The problem is the GSM network is very noisy and I have only 400-3400 hz frequency available for use. I try using fft ...
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1answer
60 views

How to estimate the frequency characteristics of a nonlinear chirp?

Given a partial time-domain recording of a noise-corrupted chirp that asymptotically approaches a frequency, and the function that determines the non-linearity, how can I accurately estimate the final ...
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1answer
123 views

How to generate IQ component for transmitting 2FSK

I am trying to generate IQ components for 2FSK modulation. I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
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1answer
61 views

Frequency Modulation to arbitrary Audio signals [closed]

I understand how FM synthesis works, but I was wondering how to FM arbitrary samples or part of samples. I.E any frame of audio samples. Further more the modulator can itself be an arbitrary frame of ...
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2answers
34 views

Homodyne and heterodyne detection

Very basic question here. I searched it on the net but cudn't get very convincing answers. Can anyone explain me Homodyne and Heterodyne detections in rf domain. Mathematically is much appreciated.
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1answer
85 views

What is the mixed numerology in OFDM

In order to meet the user requirements in the next generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
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1answer
54 views

Frequency modulation implementation without trig functions

https://dsp.stackexchange.com/a/1087 This answer suggests generating a sine wave using complex phasor multiplication. At each step the phasor is multiplied by another complex number (omega) to rotate ...
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1answer
164 views

How to convert sampled real audio signal to it's IQ components for IQ modulation?

So my question is this: How to convert sampled real audio signal to it's IQ components for IQ modulation? For instance: WHen I have my DSP or FPGA receive a audio signal through a ADC, which is just ...
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3answers
134 views

What is the algorithm to do frequency modulation?

I'm familiar with audio synthesis, oscillators etc. I'm now trying to implement my own software algorithm to do FM as described by https://en.wikipedia.org/wiki/Frequency_modulation. What I have ...
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2answers
109 views

Software to extract frequency spectrum data from an audio file

I've been trying to learn how computers recognize musical notes, and I found apps like spectrogram which shows the frequency spectrum of a sound, but what I need is the data which is plotted or the ...
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1answer
33 views

Can I alter audio recording frequency without altering the way it sounds? [duplicate]

Is there a way to increase frequency of an audio, for example (OK GOOGLE) recording of someone to inaudible range without change the way how it sounds? i.e >20000 KHz or <20 Hz. A simple increase ...
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1answer
83 views

About phase unwrapping

I am not too familiar with phase-related problems so I need some suggestions or corrections in a problem that might be an old but easy one. Here is my problem: given a complex signal: $$y(t) = e^{j\...
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4answers
74 views

How to isolate overlapping FM signals?

Analogue radio stations often have a range of frequencies that they can use. Different transmission towers will transmit on different carrier frequencies in this range, because the signal takes time ...
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1answer
82 views

What's the relationship between the parameters of this noise generator and the gaussian curve it produces in the frequency domain?

This algorithm produces a sequence $y$ having a magnitude spectrum that resembles a normal distribution, peaking at frequency $\omega$: $$b[n]=(1-\sigma)b[n-1]+\frac{\sigma}{\omega} C$$ $$p[n]=p[n-1]+...
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1answer
169 views

Carrier Recovery, Frequency and Phase offset in (CP)FSK

I wanted to ask what exactly is meant for phase recovery of signal (at least intuitively). I have a working example of an acoustic fsk modulation and demodulation software but i don't know how to ...
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1answer
339 views

FM demodulation with arctan

I am trying to demodulate a FM signal with a RTL-SDR and python using the arctan method. From here I know that $$ \frac{d}{dt}\arctan(\frac{q(t)}{i(t)}) = \frac{i(t)\frac{d}{dt}q(t)-q(t)\frac{d}{dt}i(...
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1answer
114 views

Frequency modulation of $m(t)$ in MATLAB

I have a message signal defined in the below interval $$ m(t)=\begin{cases}1&, 0\leq t < \frac{t_0}{3}\\[2ex] -2&, \frac{t_0}{3}\leq t <\frac{2t_0}{3}\\[2ex] 0&, \frac{2t_0}{3}\leq t ...
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1answer
74 views

Increase Radar Detection range using Modulation

I have been reading about pulse compression which helps with the range resolution. In my application I do not need to measure the range of the object however I am more interested in boosting the SNR ...
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1answer
46 views

Better way for fine-tuning to FM signal

I'm looking at fine tuning the frequency to a known FM broadcast automatically. (from complex signal) My beginner's idea is to either: lowpass filter to get ~2x the bandwidth visible do the frequency ...
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0answers
74 views

low-frequency amplitude with phase modulation of low Hz carrier

I am writing an FM/PM synthesizer, using Java. For the most part it works pretty well. What I am curious about is an attempt to use a low frequency tone as a carrier. By low frequency, I mean in the ...
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0answers
20 views

How training symbols in OFDM are used to estimate channel state information [duplicate]

I would like to know how the training symbols in HT-LTF preamble field is sent from Tx to Rx and used to calculate CSI (channel state) and create a matrix on the receiver.
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1answer
255 views

FM demodulation

I have a frequency modulated signal. My problem is the following: The sidebands are asymmetric. Meaning that the amplitudes of the sidebands left and right are not equal. Does anyone know what this ...
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0answers
50 views

Angle harmonic distortion in FM modulation

As you know the output form of FM modulator is something like this: $$s(t)=A_{C}\cos(2\pi F_{c}t+\beta \sin(2\pi F_{m}t))$$ where $\beta$ is the phase deviation. I want to know why in this book the ...
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2answers
279 views

FM signal detection

I'm just playing around with cheap RTL based SDR dongle and I wanted to implement a simplistic FM radio receiver. I managed to get mono sound with no problem, however I decided to implement automatic ...
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1answer
52 views

MATLAB produces too short output for frequency modulation

I have a voice data contained in a vector. Vector length is 118796 and sampling frequency is 8000 Hz. So it's around 15 seconds of voice data. When I doing frequency modulation with fmmod (Carrier ...
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2answers
538 views

How to Design a Pre-emphasis filter knowing the gain, a zero and a pole?

I am simulating an FM radio signal in order to use it as a waveform in passive radar; for this purpose I'm following an article: Analysis and Emulation of FM Radio Signals for Passive Radar In a ...
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1answer
121 views

FM modulation audio 50 Hz – 16 kHz MATLAB

I'm trying to modulate in FM an audio signal $x(t)$ coming from a microphone which works from 50 Hz to 16 kHz in MATLAB. But the problem is that I want a FM Bandwidth of 25 kHz at the output of ...
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0answers
90 views

Help identifying modulation type of unknown signal

I have a hard time figuring out what kind of modulation this is, mostly due to totally limited knowledge. It looks like dual sideband with carrier (DSB-FC) with FM modulation of the data, ...
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1answer
438 views

Hilbert Transform of an FM Signal

The Hilbert Transform of an Amplitude Modulated signal returns the envelope of the signal. What does the Hilbert transform of a Frequency Modulated signal return? How can I use the Hilbert Transform ...
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2answers
1k views

How does complex data of an FFT and IQ modulation differ?

If I have an arbitrary time domain signal (e.g. a simple cosine) i can sample it with an ADC and get a time discrete representation. I can perform an FFT on the samples and get a complex output. The ...
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1answer
70 views

How does the earphone cable in a mobile phone pick up the FM reception?

As I understand, the RF frequency-modulated signal centered in the range of $88-108\textrm{ MHz}$, is picked by the earphone antenna and is directly sampled by the sound card adc at $48\textrm{ kHz}$ ...
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2answers
397 views

Formula of frequency modulated sine wave from data points

I'm trying to determine the formula of a variable frequency sine wave based on the values of max1, max2, min1 and min2. y(0) isn't necessarily 0 and I can assume the frequency increases or decreases ...
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0answers
45 views

Is interpolation required when performing PSOLA?

As far as I understand it, PSOLA consists of simply taking 2 (windowed) periods, and overlapping them at a certain distance with another 2 periods. My question is, am I simply overlapping these ...
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1answer
945 views

difference between GMSK (Gaussian Minimum shift keying) and GFSK (Gaussain frequency shift keying) [closed]

I am unable to differentiate GMSK and GFSK. How do the modulation techniques differ in Tx? How do their receiving techniques differ..?
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1answer
117 views

How is multiplexing on FM signals performed? [closed]

How does multiplexing differ from FM signals to AM signals. If both FM and AM shift the message signal in frequency, then is there a difference between multiplexing for FM or AM signal?
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1answer
559 views

Impact of modulation index in FM

If I have the spectrum of a FM modulation, does the frequency of the carrier disappear when the modulation index is too big? Does the amplitude of any side band depend from the modulation index? And ...
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2answers
688 views

IQ FM Demodulation of Wow and Flutter Signal in Software

Background: I have a recording device that exhibits Wow and Flutter, or periodic frequency deviation. I use this device to record a calibrated 3.15kHz test tone from a tape film to generate a .wav ...
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2answers
422 views

How does the RaspberryPi radio hack convert digital GPIO signals to an FM signal?

After having looked at various explanation of how the RaspberryPi FM transmitter hack works, I realize there are some fundamental pieces missing. Most explanations talk about how to construct a ...
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1answer
156 views

What is the frequency response function for an input through a differentiator and mixer?

Through the differentiator, the frequency response will be $j \omega X(j\omega)$, but what about through a mixer with $\sin(\omega_ct)?$ Will it be $$\frac{1}{2j} j\omega\left[X(j(\omega-\omega_c))-...
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0answers
71 views

Determining SNR for cpfsk signals to be embedded in an antenna scenario

I'm trying to embed cpfsk signals, I myself modulated, into a scenario I've gotten from an antenna. Im using the the Carson Rule to determine the bandwidth of a cpfsk signal: Carson Rule: 2 times ...
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1answer
529 views

Combining 2 sinusoids of equal amplitude with different frequencies into 1 new “wave”

This question is about combining 2 sinusoids with frequencies $\omega_1$ and $\omega_2$ into 1 "wave shape", where the frequency linearly changes from $\omega_1$ to $\omega_2$, and where the wave ...
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1answer
172 views

Recommendation for good ressources on digital processing and D-QPSK

I've been a C++ developer for 10 years. Quite high level. And I am completely new to Digital Signal Processing. I am trying to implement a Software Defined Radio. Specifically I am trying to receive ...
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1answer
42 views

Noise floor of a FM duplex

If these 2 signals, that form this duplex, have ranges of 15-30 [kHz] and 30-45 [kHz] using: $NoiseFloor_{dBm} =10\log _{10}(k\times T_{0}\times 1000)+NF+10\log _{10}(BW)$ (formula from wikipedia) ...
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1answer
210 views

Biquad cookbook formula for broadcast FM de-emphasis?

Can a simple IIR biquad filter be used as an audio de-emphasis filter for broadcast FM radio? If so, how does one translate the filter requirements (50 uS time constant in the U.S.?) into parameters ...
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1answer
46 views

Please help me understand this FM carrier frequency inequality

The link of the statement is evidenced in this book: I don't understand how equation 85 come? I try to use Carson rule to see this inequality but turns out I have $2 \Delta f$ instead of $3 \Delta f$....
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2answers
4k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
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2answers
1k views

Quadrature modulation for FM and AM

This might be a naïve question, are these correct statements? Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and ...
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1answer
112 views

Receiving frequency modulated signal

I have two questions: If the FM radio at the receiver mixes with a another frequency to bring down the carrier frequency, wouldn't that affect the message signal? In today's digital world, why the ...