The RadioInstigator: A $150 Signals Intelligence Platform • Hacker News Board

Re: The RadioInstigator: A $150 Signals Intelligence Platform

#21

Post by jcims » Sun, Jun 09, 2019, 1:20 PM UTC

cinquemb wrote: post #18

jcims wrote: post #16

Earlier quoted context omitted.

It's not RF snobbery, the point is that this approach to transmitting RF signal is shitting all over the spectrum with harmonics and potentially interfering with other legitimate activity.

Yeah, a completely insurmountable problem at hand there that totally ruins any utility anyone could get from something like this…

Sure, you can get shielding and bandpass filters, but by then you're back at $100 bucks and have terrible radio to boot. The Pluto and Lime Mini are very capable transceivers for ~$150.

The RPi isn't going to bring down airliners and start WWIII, but radio spectrum isn't going to work if people don't cooperate and be good neighbors.

Re: The RadioInstigator: A $150 Signals Intelligence Platform

#22

Post by crankylinuxuser » Sun, Jun 09, 2019, 8:46 PM UTC

extra88 wrote: post #5

amingilani wrote: post #2

Wait, an antenna connected to the GPIO pin on a RaspberryPi for transmissions? Correct me if I'm wrong, but doesn't the Pi output square waves, that would cause harmonics if transmitted?

Yes, the Pi only has digital pins. I didn't really watch the video but I assume any antenna is connected to another board and that board is controlled through the Pi pins. Actually, looking at the photo of the internals, it looks like the only thing connected to GPIO is the GPS board, all the radio hardware is connected to USB ports.

Hey! I'm the creator of the RadioInstigator.

Turns out, after reviewing the interference from a GPIO pin, is actually very low (about 5% non-target frequency). I do understand I still have to deal with a comb filter output, but is minuscule from my inspections.

Im working on building a programmable filter network with independent low and high bandpass filters. But nothing available for the amateur market is sufficient. There's some stuff for the Ka and Ku bands (high microwave bands 12GHz-40GHz) but nothing for 50MHz-1200MHz. Nobody except for SigInt really cares about such a broad set of frequencies.

Re: The RadioInstigator: A $150 Signals Intelligence Platform

#23

Post by crankylinuxuser » Sun, Jun 09, 2019, 8:55 PM UTC

amingilani wrote: post #6

extra88 wrote: post #5

Earlier quoted context omitted.

Yes, the Pi only has digital pins. I didn't really watch the video but I assume any antenna is connected to another board and that board is controlled through the Pi pins. Actually, looking at the photo of the internals, it looks like the only thing connected to GPIO is the GPS board, all the radio hardware is connected to USB ports.

He says he uses the GPIO 4 pin[0], and recommends using a bandpass filter [0]: https://youtu.be/Hyq6_IZ-2fE?t=1197

Thats why I need to make a programmable filter network...

The antennas for Tx/Rx are rated for 50MHz-1200MHz. The Rtlsdr is capable of 24MHz-1.7GHz, and the Rpitx is capable of 100KHz-1.5GHz.

Using a generic bandpass from 50MHz-1200MHz would allow combing down the powers of said frequency. Whereas a proper filter network could selectively notch out a few MHz window to prevent spurious transmissions. That device would also be very useful for things like the HackRF, PLUTO, and LimeSDR. As much as they claim they generate clean signals, they still have problems with harmonics, sometimes at weird powers (as in fractional exponents, not wattage).