# Questions tagged [frequency-modulation]

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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 ...
1 vote
36 views

### 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 ...
65 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 ...
1 vote
100 views

### 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,...
1 vote
75 views

### Properly FM Demodulation & Display baseband FFT in QT using QTCustomPlots

I am having trouble trying to display the baseband signal because it looks incorrect. How do I properly display the baseband signal? Should I be doing a float to complex transformation? Am I doing ...
1 vote
129 views

### 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 ...
123 views

### 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 ...
53 views

### 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 ...
877 views

### 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 ...
116 views

117 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 ...
108 views

1 vote
252 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 ...
513 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 ...
114 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 ...
1 vote
669 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?
1 vote
421 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: ...
5k 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: ...
124 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 ...
223 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 ...
46 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 ...
834 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 ?
45 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 ...
230 views

### 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 ...