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FSK or Frequency-Shift Keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of carrier waves.

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2FSK decoder - resampling

I am developing a 2FSK decoder and this is my first endeavour in DSP. The purpose is to conned to a popular SDRs(rtl-sdr, Airspy) and decode RTTY transmission from High Altitude Balloons (HAMs hobby). ...
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1answer
41 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
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29 views

Beeping two tones in ALSA

I am trying to make a FSK modulation tool in C. Here is my test code: ...
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1answer
90 views

Why are the mark and space tones of these FSK signals reversed?

I'm working on a project involving FSK-modulated signals. I'm trying to reverse-engineer these signals to determine the preamble pattern used, because the protocol is proprietary. Shown below is a ...
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2answers
155 views

Mystery signal - FSK, BPSK?

I have a mystery audio signal that I need to decode, it's from a discontinued product. Inspecting the object code shows a module called decodeFSK so that suggests ...
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13 views

How to compensate when nsamp is not integer with Matlab

I'm trying to demodulate some FSK signals I got using Matlab. I understand how the fskdemod function works, but I don't know how to compensate the data obtained if <...
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3answers
999 views

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

I'm writing an example on transmitting data through sound betwwen 2 computers. Some requirements: The distance is very close , i.e the 2 computers are basically adjacent to each other Very little ...
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31 views

Correlation of FSK modulated PRBS - confused!

I'm trying to use SIMULINK to investigate the auto-correlation of a PRBS sequence when 2-FSK modulated. The correlation results I am getting don't make sense to me. I expected the auto-correlation to ...
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1answer
88 views

Destructive interference on the Autocorrelation of the time signal of periodic CPFSK-signals.

An FSK-signal with a frequency-shift $\Delta F$, a symbol-stream $x$, $x(n) \in {\{-1,1}\} $ and symbol duration $T$ has the complex envelope: $$f[x](t)=\exp\left(2 \pi i \Delta F T \left(\sum_{l=0}^{...
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0answers
42 views

How does bandwidth affect a modulated digital signal? [duplicate]

I'm currently reading up on how the lower layers of the ISO/OSI model work and I don't quite understand how broadband communication works yet. Suppose I want to send some data from point A to point B ...
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1answer
167 views

FSK: non-integer vs integer rmodulation index, peculiar peaks

I've been experimenting with frequency shift keying (FSK) and found a peculiar pattern I cannot explain. I noticed that there is a significant change to the shape of the power spectral density of the ...
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1answer
360 views

Understanding BFSK Modulation (MATLAB/Simulink)

Could someone explain to me BFSK Modulation on the Simulink model below? The simulation above simulates a binary FSK system with a correlation (or matched filter) receiver. I have to understand the ...
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1answer
432 views

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

Let's say that I have a 2-FSK signal recorded so that the SNR is around 20 dB and the noise seems to be more or less white. The distance between tones is greater than the minimum distance needed for ...
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1answer
518 views

Avoiding DC spike while decoding FSK signal

I am using the Quadrature Demod module in GNU Radio to decode an FSK signal, but the signal is appearing quite noisy. It has two distinct peaks centered around the advertised frequency, but they are ...
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2answers
396 views

CMA Equaliser and FSK

I'm looking into equalisation for FSK over HF channels for Digital Voice applications. As a starting point, I am trying to understand the CMA algorithm. I found a nice CMA Matlab example for BPSK in ...
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1answer
46 views

Defending Continuous values using Error Correction Codes

Say I'd like to transmit, using FSK modulation, a 100-bit packet which has a continuous field. I'd like to protect this value with an error correction code but an error in the MSB of this value is ...
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2answers
91 views

Why does AFSK only trasmit in binary?

According to Wikipedia, audio frequency-shift keying (AFSK) is done by using binary FSK, i.e. 2 tones of different frequencies, a tone for the 1 bit and a tone for the 0 bit. But isn't it possible ...
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1answer
732 views

MFSK vs FSK: Why BER decreases increasing the symbols

My question is related to the performance of 2-FSK modulation scheme against M-FSK (M > 2). From the SNR vs BER curve it seems that as the number of tones (frequencies) increases the BER decrease for ...
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2answers
3k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
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1answer
1k views

The difference between MSK as CPFSK and OQPSK

I am working on MSK simulation. I have read the Chapter 5 of book entitled Digital Modulation Techniques by Fuqin Xiong. It is said that MSK can be viewed as a Sinusoidal Weighted OQPSK or CPFSK. If ...
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1answer
199 views

Detecting frequency when frequency is not sufficiently greater than baud rate

I'm writing software this software for decoding audio samples of FSK data back to bits (ASCII, etc). The software is working really well at this point for decoding FSK when the mark and space ...
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1answer
448 views

FSK analysis: only ever find one frequency

I've trying to write this software as part of my amateur radio and SDR hobby for analyzing various two-level FSK signals. I'm very new to DSP but have been having a lot of fun so far learning more ...
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1answer
3k views

FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy so any help about the bit timing recovery would be very appreciated. Currently I implemented the ...
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2answers
4k views

What is a $BT$ (Bandwidth-Time) product with reference to modulation?

I would like to know what does Bandwidth-Time product mean. I understand that Bandwidth ($B$) = 1/Symbol Time ($T$), hence $BT = 1$. But how can it vary? What is its significance? e.g. When we say ...
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1answer
2k views

Demodulating FSK audio in Python

I am trying to write a Python script that can demodulate an FSK modulated audio file and return the data encoded in the audio. The data being transmitted is GPS NMEA strings which are embedded as the ...
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238 views

FSK audio spectrum for demodulation

I am working on Python script to demodulate FSK audio signals. The audio signal contains GPS NMEA strings. I am a beginner in DSP, but trying to work my way through this problem. I think this is a ...
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255 views

FSK demodulator by integration if the samples per symbols is 2

Say I have a binary FSK with +f and -f frequencies and I have two samples per symbol. Let's consider the "1) multiply with <...
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1answer
92 views

How to do base-band simulation of coherent detection of M-ary orthogonal signals?

I currently have a complex base-band simulator for non-coherent detection of M-ary orthogonal waveforms (such as M-FSK). I run the noisy signal through M correlators at lag=0, compute the magnitude ...
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0answers
1k views

Minimum bandwidth condition in FSK

I know that FSK occupies a larger bandwidth compared other keying schemes, $$ BW= f_1 -f_2 +2R_b $$ where $f_1$ and $f_2$ are carrier frequencies and $R_b$ is the bit rate. For achieving a ...
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0answers
361 views

How do I decode(demodulation) and get original data from audio sample data

Here I'm talking about the less-than-ideal situations, in other words, the audio sample data may have burrs or error bits in it. Encode and decode theory: I am using FSK to encode my original binary ...
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1answer
313 views

Gray code and M-FSK

Does using a gray code mapping with M-FSK improve the BER performance vs no mapping? I know it helps QAM, and it makes intuitive sense. Doesn't seem as clear cut for M-FSK.
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305 views

BFSK modulation what signal the transmitter actually sends?

I am trying to understand how modulation with carriers works(transmission part). I will express my question in terms of BFSK for simplicity. Let us condiser BFSK modulation with symbols {1,2}. Then ...
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1answer
729 views

Detecting FSK near real time with c#

I try to detect some FSK signals made by audio in near real time. I know that I will get some latency. In the start I try to detect some tones of 10Khz in a duration of 75ms. That is achieved by a ...
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1answer
90 views

Bandwidth of a trimmed sinus wave

I generate a sinus which duration is 15ms and frequeuncy of 13KHz. Is its bandwidth is (1/15ms) ? Or in other words, BW = 66.6Hz? I ask that because I have two freqs in my system: 13K & 13.1K. I ...
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54 views

Changes of phase in high frequency makes the speaker “clicks”

I modulate some data over sound in a 17.7Khz and 17.8Khz. It works like an FSK with a pulse duration of 0.015sec. When playing a string the speaker gives a very strange noise that it seems to be the ...
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372 views

Detection of an FSK Signal

This is probably as basic a question as it gets, but still the answer eludes me. I have a function from a library that I can use to both modulate, and demodulate an FSK encoded piece of data. For the ...
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2answers
52 views

SigLib FSk Function: SDA_FskModulate

I would like to implement the example code from SigLib's example "fsk.c". The defines are below #define SAMPLE_LENGTH ((SLArrayIndex_t)512) #define NUMBER_OF_LOOPS ...
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0answers
261 views

Detect FSK high/low bits in presence of noise with only simple processing

I'm currently in the process of writing DSP code, based on the amazing RTLSDR project, and using this as a vehicle to teach myself the basics of DSP (I have an extensive background in software ...
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1answer
825 views

Spectral effects of multiplying a signal by itself?

This has to do with creating the synchronization circuit for MSK in a DSP as described in "Minimum Shift Keying" by Subbarayan Pasupathy published in IEEE Communications Magazine. At the beginning of ...
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2answers
225 views

Noise from CPFSK

I am programmatically generating a CPFSK encoding, and between shifting from two frequencies, there is extra noise generated by my speaker. For instance, going from 18375hz to 18900hz, there is extra ...
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1answer
6k views

Orthogonality of FSK modulation for non-coherent detection

For an FSK modulation with coherent detection, in order to ensure orthogonality, the frequency separation between symbols is $ \Delta f=f_2 - f_1 =1/2T$. However, in case of non-coherent demodulation, ...
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198 views

Finding BER, using FSK at GSM network

I would like to ask, cuz I don't know much from that, how we can find the BER at a GSM network (uplink & downlink separately of course), while we are using FSK modulation? I mean the equations ...
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1answer
190 views

How should I modulate a $16$ bit input using FSK?

I need to graph a $16$ bits binary sequence, assuming that it'll be a FM analog signal I need to apply FSK to it. So, I think I should use the formula $A \cos(2\pi f_1 t)$ for binary $1$'s $A \cos(...
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2answers
3k views

Why is Frequency Shift Keying more immune to noise than ASK?

Is it because noise manifests itself in the transmitted signal's amplitude?
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2answers
5k views

PC-to-PC data communication over Sound FSK / PSK / DSSS

For fun and work I've to implement a java based application that can Encode text or data to sound and transmit using PC's speaker and on the receiving side is a microphone with decoder software. I ...
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0answers
2k views

Demodulation of noisy AFSK signal

I'm trying to implement a software audio modem with FSK to transmit and receive short digital data between two devices (e.g. a PC and an iPhone) so I'm simulating simple cases study using Scilab/...
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0answers
271 views

AFSK clock recovery in noise

What algorithms are available for optimizing estimated bit clock recovery of an audio FSK modulated signal over an extremely low S/N ratio channel? (e.g. barely audible due to high ambient noise and ...
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3answers
12k views

How to demodulate an AFSK signal in software

I am trying to transmit binary data from one device to another over an audio channel (speaker/mic). I use AFSK (Audio Frequency Shift Keying) as in Packet Radio, with $1200 \text{ Baud}$ and two ...
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2answers
4k views

Spectrum of FSK signal

I have implemented a simple V.23-like FSK modem in C here. The peculiarity of the chosen modulation is such that 0's and 1's are sent as tones of two different frequencies (2100 Hz and 1300 Hz ...