'm just playing around with cheap RTL based SDR dongle and I wanted to implement a simplistic FM radio receiver. I managed to capture by the dongle the IQ samples (raw data) that has what I have transmitted, so I want to do by matlab or whatever a simple reciever for detection what I have transmitted (RF communication signals)
My first approach was to detect peaks in power spectrum, however the result did not satisfy me as only a few channels were detected, much less than using a cheap standalone radio receiver. but that's didn't work well..
Then I approached the fact that what I'm looking for is frequency modulated signal and construct my won SDR RTL demodulator for recieving the required data from IQ SAMPLES(MODULATED SIGNAL) , but Im stuck in building that demodulator in matlab .... what I have done yet is two matched filters for detecting the signal at specific frequency that I transmit but still not succeeding to finish the demodulator successfully .. could anyone help me what could I do to implement demodulator by matched filters in matlab?
the input is the captured raw data (IQ samples ) that Im sampling by RTL SDR dongle ..


thanks alot for any assistance

 

Sounds very math intensive. Probably have to start with the mathematical description of an FM signal. https://en.wikipedia.org/wiki/Frequency_modulation. Way above my pay grade...

 

Your decoding FM you say, yet you also mention detecting amplitude, which is not FM.
you also mention decoding two tones, that is not FM.

Sounds what you have is AM.

If you want to decode a few tones, then Goertzel is your friend

https://en.wikipedia.org/wiki/Goertzel_algorithm


may be a bit / lot more info on how your constructing your transmission is in order.

 

Thanks guys, but about parameters deviations /symbol rate ..etc , where I can find a good explanation to understand digital signal processing ? could you hand me a link online for learning about RF frequency and how transmitter/receiver in digital processing works?

 

David, the most valuable source for information about RF design, at least for me, is the ARRL (Amateur Radio Relay League) Handbook. Covers theory and sample circuits.

 

David, the most valuable source for information about RF design, at least for me, is the ARRL (Amateur Radio Relay League) Handbook. Covers theory and sample circuits.

there's not online handbook pdf for it?

 

Hello,

The eye has a lot of RF related books in the electronic arhive:
https://the-eye.eu/public/Books/Electronic Archive/
There are also some ARRL books on that page.

Bertus

 

I have a hardcover (very thick) book for it from the 1980's when I did a lot of RF work. I just checked and there are now variations of it including an eBook.

 

Hello,

Also the following books might interest you.
RF Design Basics by the RSGB
https://www.box73.de/product_info.php?products_id=1463
Experimental Methods in RF Design, Classic Reprint Edition by the ARRL
https://www.box73.de/product_info.php?products_id=1966

Amazon also has a lot of ARRL books available:
https://www.amazon.com/s?k=arrl+han...s,236&ref=sr_nr_p_n_feature_nine_browse-bin_1

Bertus

 

APPRECIATED!