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Questions tagged [frequency-modulation]

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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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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 ...
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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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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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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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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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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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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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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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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 ...
good_omen92's user avatar
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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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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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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)...
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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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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 ...
John Jin's user avatar
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Calculating amplitudes of FM Sidebands

How are the amplitudes of FM sidebands calculated? E.g. when negative frequencies are reflected back and their amplitudes added to any existing positive frequencies at that band, how are the ...
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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 &...
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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
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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 ...
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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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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 ...
Ryan's user avatar
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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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2 answers
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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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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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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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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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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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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 ...
Ulrich Vormbrock's user avatar
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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 ...
cherryBom's user avatar
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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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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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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.
rider99's user avatar
-1 votes
1 answer
162 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 ...
fredyeah's user avatar
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1 answer
105 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 ...
viraptor's user avatar