Use demodulated signals with electronics, off-pc

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JelleFlies
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Use demodulated signals with electronics, off-pc

Post by JelleFlies » Mon Apr 15, 2019 8:23 pm

Is there a way to use SDR received and demodulated signals outside of the PC, connect it to electronics?
I guess setting up the audio output (using GNURadio) would be a possibility, but you are restricted to AC signals and may loose bandwidth.

Anyone have any experience with this?

rtlsdrblog
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Re: Use demodulated signals with electronics, off-pc

Post by rtlsdrblog » Tue Apr 16, 2019 9:51 am

What do you mean by connecting it to electronics?

If you have a TX capable SDR you can simply restransmit the signal being received, but I don't understand what the point of that would be, unless you're doing some DSP to the signal in software first.

JelleFlies
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Re: Use demodulated signals with electronics, off-pc

Post by JelleFlies » Tue Apr 16, 2019 10:24 am

I mean connecting the received baseband signal to an external microprocessor, like PIC, AVR or even FPGA's.
So that you could use a received bit-stream to control robotics, light systems, domotica, etc.

Does that clear things for you?

hotpaw2
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Re: Use demodulated signals with electronics, off-pc

Post by hotpaw2 » Tue Apr 16, 2019 6:11 pm

Depends what you mean by a PC.

I plug my RTL-SDR directly into a Raspberry Pi 3 B. A Raspberry has enough USB bandwidth and enough processing speed to demodulate the raw IQ data from an RTL-SDR, and to detect many types of signals. A Raspberry Pi also has digital IO pins, similar to an Arduino, to control external hardware widgets.

An AVR-based Arduino has too slow a processor to decode the IQ signals, and an ARM based Arduino likely does not have enough USB bandwidth for the lowest RTL-SDR sample rates. Whereas a Pi probably has at least 10X more compute power than a PC of 20 years ago, and runs a more sophisticated operating system. But since it's about the same size as the original Arduino Uno, do you call it a PC?

JelleFlies
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Re: Use demodulated signals with electronics, off-pc

Post by JelleFlies » Tue Apr 16, 2019 8:10 pm

That may be a good solution, I think I will be able to write the demodulated signal to one of the GPIO pins, using Python. I could even use that signal to modulate another transmitter, but that is a different story.

Thanks for thinking with me!

rtlsdrblog
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Re: Use demodulated signals with electronics, off-pc

Post by rtlsdrblog » Wed Apr 17, 2019 2:27 am

JelleFlies wrote:
Tue Apr 16, 2019 10:24 am
I mean connecting the received baseband signal to an external microprocessor, like PIC, AVR or even FPGA's.
So that you could use a received bit-stream to control robotics, light systems, domotica, etc.

Does that clear things for you?
The simplest way would be run the SDR on a Pi 3, and demodulate the signal in software there. Do whatever you need to do to extract the data + whatever logic you need, and then control the electronic devices via GPIO/I2C/WiFi/BT etc. I don't see any reason to output the demodulated audio signal to the electronic devices. The Pi3 should be powerful enough to handle everything.

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