47
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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, ...
- 32.5k
10
votes
Accepted
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 ...
- 3,426
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 ...
- 15.4k
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-...
- 13.7k
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-...
- 32.5k
5
votes
Accepted
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 ...
- 2,710
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 ...
- 28.4k
4
votes
Accepted
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 ...
- 2,710
4
votes
Accepted
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 ...
- 269
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 ...
- 35.7k
4
votes
Accepted
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 ...
- 55k
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 ...
- 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 ...
- 1,802
2
votes
Accepted
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 $\cos(2\pi f_0t)-\cos(2\pi f_1t)$. ...
- 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 ...
- 24.8k
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 ...
- 32.5k
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 ...
- 92
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 ...
- 33
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 ...
- 3,042
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?...
- 20.9k
2
votes
Accepted
IQ Constelation Diagram of FSK signal
The OP is correct with the intuition that the IQ diagram for the FSK signal should remain on the unit circle. All forms of FSK are constant envelope signals, as we see clearly in the time domain plot ...
- 55k
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 ...
- 55k
1
vote
Why distance index between 2 frequencies in M-FSK has to be odd?
To me it seems that you are asking why there are an even number of frequencies centered around $f_c$ (Hopefully this UNICODE art renders OK):
...
- 13.7k
1
vote
How to decode a binary Signal in a wav file into binary - sent here from stackoverflow
What you are looking for is a format called SSTV, you can recognize it usually by its distinctive tone at the start, like in your audio file.
I haven't seen people decode it manually, in my (very ...
1
vote
Accepted
Why in FSK the phase shift is allowed?
My first question is, why should we allow the signals have different phases?
Counterquestion: Why should they not be allowed? Enforcing continuous phase can make systems more complex, without any ...
- 32.5k
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 ...
- 32.3k
1
vote
Accepted
Destructive interference on the Autocorrelation of the time signal of periodic CPFSK-signals.
After thinking for a while i came up with my own proof. I hope it is helpful to you and correct!
Definition: Frame-Structure
The frame structure used in the following is one of one-periodic signals, ...
- 189
1
vote
Accepted
Demodulation of FSK signal
For this specific waveform as described, the following would demodulate the signal from the Frequency Shift Modulated Input into a square wave output:
This works given the duration of the "0" symbol ...
- 55k
1
vote
Accepted
Methods for aligning FFT bins with an FSK signal
Before I address your question, I'll suggest that using a frequency domain technique (FFTs) to demodulate inherently time domain data (a time series of sequential data symbols) won't be very practical....
- 2,710
1
vote
Accepted
How to solve signal MFSK or FHSS question (received signal+ noise+jamming)
$$A\cos(2\pi f+\theta_1)+B\cos(2\pi f+\theta_2)=C\cos(2\pi f+\theta_3)$$
where
$$C=|u|\quad\textrm{and}\quad \theta_3=\arg\{u\}$$
with
$$u=Ae^{j\theta_1}+Be^{j\theta_2}$$
The constant $C$ can be ...
- 92.5k
Only top scored, non community-wiki answers of a minimum length are eligible