Somebody interested by RTL/SDR ?

[Dzandaa]

Hi,

Somebody interested by RTL/SDR in Pascal?

https://www.rtl-sdr.com/about-rtl-sdr/

I have a skeleton program with RTL/SDR wrapping in Windows and Linux.

If somebody is interested to continue the development, I can share it.

B->

[Gigatron]

Hi

It looks very interesting, you do a good job, perfect.

[BlueIcaro]

Hello, I'm have interest as HamRadio Amateur.
But May be you can upload to a Github o Gitlab, and someone can fork it and continue you proyect
/BlueIcaro
P.D I have one sdr unit

[Dzandaa]

Hi,

I'm not in Github (Microsoft) nor Gitlab, but here is the code:

I'm confused with the Central Frequency and how to use it correctly with a FFT.

I can capture a buffer, set different parameters, do FFT, but I don't what to do with the position of the frequencies from related to central frequency.

Simple project for the fun.

B->

[Curt Carpenter]

It's been a few years since I was involved with learning about SDR, but one of the best and most educational ways I found to do it was using GNU Radio, web site here:  https://www.gnuradio.org/

[Dzandaa]

Hi,

Yes, I know GNU Radio, Gqrx, etc...

The idea was to have a Lazarus interface.

B->

P.S.: that version is Windows only.

[ALLIGATOR]

Hi, I've reworked your program a little bit, it's mainly to speed up the rendering/work done in the timer handler.
I also formatted the source code to my taste.
Also, it can now run under Linux

[Dzandaa]

Hi,

@ALLIGATOR:

Thank you very much, for the optimization and the porting to Linux.
My problem is to show the central frequency in the middle of the chart in relation to the buffer.

...And then to decode the data

To be continued...

B->

[ALLIGATOR]

My problem is to show the central frequency in the middle of the chart in relation to the buffer.

Please explain in more detail. Perhaps it would be easier to show with a picture?

...And then to decode the data

Do you have any ideas on how to do this?

[Laksen]

When you do a normal forward FFT the output will be an array of frequency bins.

E.g for a 1024 point FFT at a samplerate of Fs, index 0 will be 0 Hz, index 511 will be 511*Fs/1024, index 512 will be -512*Fs/1024, index 1023 will be -1*Fs/1024. Of course ignoring the center frequency that the RF transceiver LO is tuned to

So to fix it you essentially just switch the two halves of the FFT result (0..511 <-> 512..1023). Now index 0 will be -512*Fs/1024+Fcenter and index 1023 will be +511*Fs/1024+Fcenter

[Dzandaa]

Hi,

@Laksen:

Done

Thank you.

B->

[Laksen]

No problem

To demodulate it.. That's a big topic. What modulation is your signal using?

[Dzandaa]

Hi,
@Laksen:

Just FM Radio for the moment

B->

[Laksen]

Okay, that's a fun one. Lots of ways to do that