46 votes
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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. well, "best" is always a reduction to a single set of optimization parameters (e.g. cost per bit, ...
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11 votes
Accepted

Why do we integrate the modulating function in FM?

You need to integrate the modulating signal because frequency is the time derivative of phase. Therefore, the typical relationship from introductory calculus holds: $$ \phi_i(t) = \int_{-\infty}^{t} \...
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  • 23.6k
8 votes

Why can so little digital information be stored on a cassette tape?

High-capacity tape formats use helical scanning. Here I look at why that gives a higher capacity than linear recording with four tracks (one stereo track on each side) like in a compact cassette (C-...
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8 votes

I'm missing something when it comes to understanding FM

In addition to the perspective offered in @Ash's answer, Claude Shannon touches on FM in his paper "Communications in the Presence of Noise" (Proceedings of the IRE, January 1949). He ...
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  • 8,121
7 votes

FSK and IQ modulation

What is the advantage of performing the FSK using IQ modulation? You only need one RF oscillator operating at a single frequency, instead of having 2 (or more in the case of M-ary FSK) oscillators ...
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6 votes
Accepted

Simulation of a Frequency ramp

I waited a bit to see if someone else takes the challenge, but since there are no answers yet, I'm providing mine now.
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  • 79.2k
6 votes
Accepted

Difference between FFSK and FSK modulation schemes

Fast FSK is just another term for minimum-shift keying (MSK). In the modern literature, the term fast FSK has been almost completely replaced by MSK. There is a very good tutorial paper on MSK by S. ...
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  • 79.2k
5 votes
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Recommendation for good ressources on digital processing and D-QPSK

Wow, I'm honored by Matt L. doing what I'm often doing: Referring people to GNU Radio. The project actually has a list of recommended literature, but I don't know how well that'd fit you. It's ...
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5 votes

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

First, the answer to why you do not see a negative voltage is that the output being digital will range from 0 to the maximum digital voltage at the output (+Vs). This will have a DC offset of +Vs/2 ...
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  • 36.1k
5 votes
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Quadrature modulation for FM and AM

Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and receive radio signals. This question is ill-defined – a signal ...
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5 votes

What is the mixed numerology in OFDM

In general, it means several waveforms will coexist in 5G ecosystem. In the context of LTE-based 5G (up to now), several subcarrier spacings (hence CP) coexist. The first and foremost motivation for ...
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  • 5,720
5 votes

I'm missing something when it comes to understanding FM

Large modulation indexes are preferred because the signal-to-noise ratio has a cubic dependence on modulation index ($\beta$). $$SNR_{FM}=3\beta^2(\beta+1) CNR$$ Where CNR is the carrier-to-noise ...
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  • 642
4 votes
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Simplified equations for FM (frequency modulation) synthesis and PM (phase modulation)?

If $t$ is time, $s(t)$ is the (appropriately scaled) signal, $\omega_0$ is the angular frequency, and $\phi_0$ is a phase offset, then phase modulation is $$ t \mapsto \sin(\omega_0 t + \phi_0 + s(t)) ...
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4 votes

FSK and IQ modulation

There are many ways of demodulating the FSK signal Indeed! What is the advantage of performing the FSK using IQ modulation? Depends. Generally, IQ is the only shape you have your signal in, so ...
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4 votes
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How to estimate the frequency characteristics of a nonlinear chirp?

How about just using $\dfrac{d\phi}{dt}$ to compute the instantaneous frequency? GNU Octave code (I just made up a sample rate of 2 Msps): ...
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  • 2,390
4 votes
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Positive slope of BER with a greater frequency deviation?

This could happen as discriminator gain is increased with a filter discriminator approach since in many of those approaches the gain would be maximum and linear for small signals only and then the ...
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  • 36.1k
4 votes

Why can so little digital information be stored on a cassette tape?

Typical cheap cassette tape recorders and players in the 1970's used audio circuitry that did not have a completely flat frequency response and added a lot of phase distortion (mostly inaudible to ...
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  • 33.8k
4 votes

Why can so little digital information be stored on a cassette tape?

You have already selected your answer, but I would like to put a few more lines. First of all, objecting to Marcus, I think that your first assumption is correct! We can store one hour of almost CD ...
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  • 26.6k
3 votes
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How does the RaspberryPi radio hack convert digital GPIO signals to an FM signal?

I just skimmed https://github.com/SaucySoliton/PiFmRds/blob/master/src/pi_fm_rds.c#L454 and from what that code looks like, it initializes a clock generator to run at an adjustable clock. Then, it ...
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3 votes

Impact of modulation index in FM

Assuming an FM modulation of a sine wave of frequency $f_m$. Theoretically, the modulated signal is an infinite sum of cosines at the frequencies $f_c + nf_m$ ($n\in \mathbb{Z}$) which the amplitudes ...
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  • 168
3 votes

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

With GMSK, the frequency modulation index is 0.5. With GFSK, the frequency modulation index is larger than 0.5 (the signaling tones are farther apart). The receiving techniques used for GMSK as an FSK ...
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  • 2,390
3 votes
Accepted

Frequency modulation of $m(t)$ in MATLAB

Integration was incorrect. I was integrating it with $dx= 1$. Doing m(j)*1/Fsoperation in the for loop, I have made $dx= 1/Fs$ now. As can be seen, frequency ...
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3 votes

How to isolate overlapping FM signals?

What if they did all use the same carrier? What you're describing is a single-frequency network (SFN). These are in common use for things that are not stupid FM broadcast. The whole truth is that ...
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3 votes
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How to convert sampled real audio signal to it's IQ components for IQ modulation?

I’ll answer the question I think you’re asking here: If you have a real valued signal that came right out of an A/D and you’d like to recover signal phase, you can use the Hilbert transform to ...
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3 votes

Homodyne and heterodyne detection

I'll assume AM DSB modulation for simplicity, but the same idea applies to quadrature modulation. I'll assume that the received signal has been properly bandpass filtered. I'll also ignore noise and ...
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  • 13.5k
3 votes

How is frequency related to data rate?

There's simply no inherent relation between carrier frequency and data rate. I assume a classical comms engineering education here, but since that most often introduces the concept of equivalent ...
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3 votes
Accepted

IQ signal FM descrimination using phase derivative

I simply use unwrapped atan2(IQ(i)) - atan2(IQ(i-1)) to estimate a discrete derivative, then low pass filter to below 15 kHz. Although with a shallow slope, the 1st order approximation to atan() ...
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  • 33.8k
3 votes

Why do we integrate the modulating function in FM?

Frequency by definition is the derivative of phase with respect to time (a change in phase divided by the change in time is frequency). You see this with the radian expression for frequency given by $...
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  • 36.1k
3 votes
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FM: Do rational ratios of carrier to modulator signals really produce harmonic spectra?

That paper (1973) is about more natural, simple and rich audio synthesis using FM (which later became Yamaha's very populer FM synthesis audio chips). In that respect, the carrier frequency is taken ...
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  • 26.6k
3 votes
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Doubt in Frequency Modulation code

When generating the sine wave, the code uses a sampling frequency to establish discrete points in the time domain. It is not continuous. This means the wave is broken up into bins that are exactly 1/...
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  • 316

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