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47 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, ...
Marcus Müller's user avatar
10 votes
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FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy… Since you say you have matched filters, and you mention non-coherent detection, I think you're ...
Marcus Müller's user avatar
10 votes
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What is a $BT$ (Bandwidth-Time) product with reference to modulation?

The $BT$ product is the bandwidth-symbol time product where $B$ is the $-3\textrm{ dB}$(half-power) bandwidth of the pulse/filter and $T$ is the symbol duration. For different applications you will ...
Gilles's user avatar
  • 3,406
9 votes

Transmit data through sound between 2 computers (very close distance)

As you have realized, the hard part of doing digital communications is carrier, symbol and frame synchronization, and channel estimation/equalization. The bad news is that you can't get around these ...
MBaz's user avatar
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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-...
Olli Niemitalo's user avatar
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 ...
GordonFreeman's user avatar
5 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 ...
Fat32's user avatar
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5 votes
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FSK: non-integer vs integer rmodulation index, peculiar peaks

With integer modulation indices, each symbol is actually an integer number of full oscillations. You DFT that, and get a sharp, discrete spectrum of tones, convolved with the pulse shape. With non-...
Marcus Müller's user avatar
5 votes
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FSK modulation with python

The phase of your output signal is not continuous, because you have implemented the phase as the output of one of two independent frequency oscillators both starting at time $0$, so their phases are ...
Andy Walls's user avatar
  • 2,710
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 ...
Marcus Müller's user avatar
4 votes

The difference between MSK as CPFSK and OQPSK

The answer to your question is yes, these two representations are equivalent. The first important thing to note is that in your formula, $d_k$ must be either $1$ or $-1$, because the frequency ...
Matt L.'s user avatar
  • 90.6k
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 ...
hotpaw2's user avatar
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4 votes
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Mystery signal - FSK, BPSK?

After playing around in GNURadio, this waveform looks like 2 level ASK bursts (OOK bursts plus some residual carrier). The carrier appears to be at 12.4 kHz. At the 44.1 ksps sample rate, there ...
Andy Walls's user avatar
  • 2,710
4 votes
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Transmit data through sound between 2 computers (very close distance)

In the end, I used DTMF (Dual Tone Multi Frequency signaling). The original DTMF has 16 signals each using a combination of 2 frequencies. But here I only used "1"(697 Hz and 1209 Hz) and "0" (941Hz ...
Dang Manh Truong's user avatar
3 votes
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Decoding a PCM BFSK signal (Bell 103)

The frequency resolution is independent of the sampling rate. Consider that in the extreme of an infinite sampling rate (continuous time), the Fourier Transform of a single FSK symbol at either 1070 ...
Dan Boschen's user avatar
  • 52.8k
3 votes

Symbol Synchronization for GFSK/FSK signals in GNU Radio

The Symbol Synchronizer block is a PLL-based synchronizer that is trying to estimate the symbol clock period and symbol clock phase (aka timing offset) based on the samples coming in that represent ...
Andy Walls's user avatar
  • 2,710
3 votes

CMA Equaliser and FSK

The confusion comes from the fact that what is tagged as "transmitted" isn't the real transmitted waveform but its baseband representation, which are $\left\{+1,-1\right\}$ symbols in 1 dimension. For ...
SleuthEye's user avatar
  • 1,802
2 votes

Why does AFSK only trasmit in binary?

There's a time vs. frequency trade-off that can work against you. At a given signal-to-noise ratio, it takes longer (and often more compute power) to reliably determine which of two frequencies are ...
hotpaw2's user avatar
  • 35.5k
2 votes
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Why does AFSK only trasmit in binary?

The three main reasons appear to be these: 1) In AFSK, it's not just jumping back and forth between frequencies. The tones must also be continuous phase. In other words, when the tone changes, there ...
Be Cn's user avatar
  • 36
2 votes
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MFSK vs FSK: Why BER decreases increasing the symbols

(I assume maintaining the same symbol duration) nope! That is usually not the case, because it would be unfair – if you send the same number of symbols per second, you'd get twice as many bits per ...
Marcus Müller's user avatar
2 votes

Detecting frequency when frequency is not sufficiently greater than baud rate

You should read Wikipedia - Minimum Shift Keying. The minimum frequency distance between two FSK tones is half the baud rate. But even at 1X the baud rate, the tones look blurred together in the ...
cassman's user avatar
  • 90
2 votes
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FSK analysis: only ever find one frequency

You can make a very simple frequency discriminator by multiplying your received signal with a delayed version of itself, followed by a low pass filter. Adjust the delay to set the frequency range of ...
Dan Boschen's user avatar
  • 52.8k
2 votes
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Understanding BFSK Modulation (MATLAB/Simulink)

So, ignoring noise, the input into the receiver multiplier coming from the channel is either $\cos(2\pi f_0t)$ or $\cos(2\pi f_1t)$. The other multiplier input is $\cos(2\pi f_0t)-\cos(2\pi f_1t)$. ...
MBaz's user avatar
  • 15.4k
2 votes

How to determine the symbol rate of a 2-FSK signal?

One approach could be to perform an FM-detection step (e.g. an atan2() operation followed by a first-order difference) to transform the waveform to measurements of ...
Jason R's user avatar
  • 24.7k
2 votes

Avoiding DC spike while decoding FSK signal

That looks very nice: I don't 100% agree with your phrasing on this one: however, my quadrature demod is capturing large amounts of noise during the idle periods. Well, the quadrature demod ...
Marcus Müller's user avatar
2 votes
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Estimating the SNR of 2-FSK

I've used the first technique before. The idea is that you have some chunk of time domain samples where you know only noise is present and use that to get an estimate of the noise power, $P_n$. Then ...
Engineer's user avatar
  • 3,042
2 votes

Clock Recovery with FSK Demodulation in GNU radio

That extra 1 and 0 could come from different signals around 431MHz. Since you are not doing any lowpass filtering you'r demodulator gets whole 400kHz band (your USRP sample rate). I'd suggest putting ...
Aladins's user avatar
  • 33
2 votes

Why distance index between 2 frequencies in M-FSK has to be odd?

So, my question is: why can't do we use any value (even and odd, spaced by 1 fd), to reduce even more the bandwidth of our signal? Has it relation to interference between symbols in frequency spectrum?...
Dilip Sarwate's user avatar
2 votes

What causes sharp peaks in the spectrum of continuous phase BFSK with Manchester coding

Typically I have seen Manchester encoding done by multiplying the original data stream with a square wave at the same date rate of the signal (so in this case it would have been 40 Hz) such that if a ...
Dan Boschen's user avatar
  • 52.8k
1 vote

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

Despite the title of the question, a 2018 IEEE Spectrum article explains: Why the Future of Data Storage is (Still) Magnetic Tape Disk drives are reaching their limits, but magnetic tape just gets ...
Laurent Duval's user avatar

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