Use demodulated signals with electronics, off-pc

[JelleFlies]

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]

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]

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]

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]

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]

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.

[LB6MI]

For a AVR; you would likely want to run a downconverter from the R820T output, in order to get a even lower frequency.

I have seen projects using a analog switch as a quadrature demodulator,
and if you add some low-pass filters you may get it slow enough to be viable.

You have quite limited ADC speed and CPU speed on those AVR8 chips.

I have gone over the math before, and you would want slow sample-rate, or there is no way you would have time to deal with the data.