Signal Demodulation. Please Help!!!

[b0rman23]

I have recorded .wav file with modulated signal! Image file attached... Anyone knows what type of modulation is used to modulate that signal[/img]

 

[albbg]

It seems a simple AM.

 

[b0rman23]

Well, maybe you right...

I'm not an expert at DSP, I just started to read about it a month ago and need someone to point me in a right direction...

maybe my bandpass filter is not right... as you said it seems like AM but AM modulation has a smooth transition between peaks, mine doesn't look like that.

I can tell you one thing for sure that it's a binary data, but I can't figure out where is 0 and where is 1 and I don't know what kind of encoding is being used

sounds simple high peak 1 low peak 0, but also there is such thing as noise which can be mistaken for 0

too many buts and ifs...so "seems like a simple AM" ???

 

[karesz]

Hi,
If its a binary datasream, you must know: are the bit times of equivalent lenght?
Hier is a fifferent time volumen to find in both cases; as for 0s & 1s too...
Or you have very much disturband signals/spikes in/on your data lines & eventulell complett electronics?
Seems if your GND lines and bypassings atent OK:-(?
K.

 

[b0rman23]

looks little bit like DSB-SC (Double-sideband suppressed-carrier transmission)

https://en.wikipedia.org/wiki/Double-sideband_suppressed-carrier_transmission

but I'm not 100% sure... the thing is that my full time job kills me I have no time for experiments

I'm using USRP running on linux (GNU RADIO),(not familiar with matlab, I have it installed but once again no time to learn it)..that's why I need somebody to point in a right direction...someone who has experience... I'm trying to demodulate RF signal that I captured, I guess I have to use some more filters first to get a better looking output

 

[karesz]

Hi bOrmqn23,
Inpossible to be aDSB signal: these one has continous phases...
K.

 

[JoannesPaulus]

can you upload the waveform so that we can do some experiments?

 

[b0rman23]

the URL is below

anyway that signal is output from band pass filter, maybe the parameters of band pass filter are not set properly and I get deformed wave? or maybe I have to use more filters to get a better looking waveform..?

If you get a chance please look at it...

 

[karesz]

Oha,
this atachament is not complete_pls repair it!!
K.

Your uploading is to check or reload...

 

[b0rman23]

karesz I'm not a technical guy that signal was taken directly from antena, the signal has low noise ratio(at least it looks like that to me), I just don't know what filters to use to make it look like something that can be demodulated into 0 and 1's when I translate that signal to mathematical numbers I don't see that sequence in that waveform

Added after 52 seconds:

ok, one second let me see whats wrong with it...

Added after 10 minutes:

ok here is URL, I can't upload it to this forum, they won't allow it

https://b0rman23.angelfire.com/testsignal.wav

 

[karesz]

To upload an attachment:
you must write first a text, load it, than select from uploaded window "edit"/click it, you becomes your uploaded text to edit it_if you wishes, & you can attach some files, click on "add" to first & after completed reload it...
K.

 

[b0rman23]

I tried to do that, but this forum rejects attachments with .wav extension

 

[JoannesPaulus]

I am afraid I cannot figure it out (I am not a modulation expert) but here is the FFT...

 

[b0rman23]

Yes I can see exactly the same thing on my fft scope when I use band pass filter(depends on how i set low and high cutoff frequency), I just try to adjust it so the signal looks like something and not just random noise.. but I don't know if parameters are right, maybe it should look differently...

what filters should I use? I have many different options available in GNU Radio

Open that file in any Audio editor to see the signal that I captured(waveform) itself. I uploaded a picture above with a segment of that signal

 

[karesz]

Hi JoannesPaulus,
I dont tel it why so is, but for me tells your FFT as follows: the modulation is distorted, or a general AM? becouse both sidebands has same power as the carrier_its not rejected (to the sidebands) or are both sidebands & the carrier with same damping out from the modulator.
The modulation frequency=4KHz (in reality a sub carrier) then has in USB & LSB same, in both case another modulation? of ca 200Hz!?

WHAT IS IT pls?

@b0rman23: Where is the 200Hz from?
Then; why is a phase changing to see yet on your FFT scope & was not on the first picture from you?
K.

 

[b0rman23]

@b0rman23: Where is the 200Hz from?
Then; why is a phase changing to see yet on your FFT scope & was not on the first picture from you?
K.

you mean the wave on 'scope plot' that goes between +0.2 and -0.3?

that signal is generated by the device that I'm capturing data from, when the device is powered up it generates electromagnetic field on a specific frequency (mhz), tuning to that frequency produces 200hz wave, performing a function on that device produces 400hz wave(that I need to demodulate)



yes that a very interesting thing that I just noticed myself!!!

I'm a beginner and don't know much about signal processing...but...

phase on scope changing and on picture not because "I Think but not 100%" the signal is modulated using two techniques maybe PSK + Something(FSK??).. if you open .wav file you'll see that the signal divided in two parts...I have no other logical explanation...

that would explain why it's different....

open .wav file

 

[karesz]

Hello,
Im sorry, but I dint never some thing with signal processing & cannot open the ".wav"-file too...

The difference between two screan shots is maybe from a digitizing/sampling effect?
K.

 

[b0rman23]

yes i convert from analog to digital...if you have no way of opening .wav file I can convert everything into numbers... ( time and amplitude value)


https://b0rman23.angelfire.com/testsignal.dat

open it as text

Added after 4 hours 56 minutes:

ok...I read a little bit more about dsp....the signal that is 200-300hz is a carrier wave...data is modulated around that carrier..interval, amplitude...blah..blah...blah...different modulation techniques.... the thing is that I don't have the original signal so the signal that I'm capturing and passing through some filters(mathematical algorithms)...the result that I get I have nothing to compare it to....because I don't know how it suppose to look...That's why I need someone who is familiar with digital signal processing who can tell what modulation that signal is based on...My friend....everything is simple if you know how..ok I understand you can't open .wav format...I don't know what system you use...you tell me in which format you want it...give me the extension (unless you use hardware scope)

 

[annum]

it is fm modulated signal