gr-tempest VS gnuradio

GR-Tempest

https://www.youtube.com/watch?v=8Bx1R_y5xSk & https://github.com/git-artes/gr-tempest

> gr-tempest, a GNU Radio-based implementation of TEMPEST, is an on-going project whose objective is to emulate and extend TempestSDR functionalities, while enabling simpler experimentation and taking advantage of GNU Radio’s functionalities and support. In this talk, I will describe the mathematical principles behind the TEMPEST attack and present how gr-tempest works. Furthermore, I will show several real-world examples including both VGA and HDMI, and the fundamental differences between both types of signals.

Its worth noting that prior to the growth of cable/satellite TV channels and the introduction of Digital TV broadcasting... the "TV Detector" was actually a real workable process. Regardless of how often their enforcement actually used them or how diligently they used them (and thus false positives). The fact the "evidence" from the vans was never used in court does not mean they could not or did not work.

"TV Detection" was actually just a civilian use of Radiation Intelligence, the kind of RF emanation that the USA has the entire TEMPEST hardening requirements https://en.wikipedia.org/wiki/Tempest_(codename) in order to prevent nation state attackers from being able to snoop data from their electronic equipment. This is a very real security principle and plenty of demonstrations out there to show how much information can be leaked from unshielded systems. You can check out gr-tempest which uses modern software defined radio hardware https://github.com/git-artes/gr-tempest. You can see pretty good demo of it here https://old.reddit.com/r/RTLSDR/comments/q59ofn/i_was_finall...

The basic truth is that over time it got harder and harder to build "simple" detectors to work out if people were using their TVs to watch the BBC (and this is the tricky part, a valid argument is "I don't watch the BBC", so they need to detect BBC channels being displayed on the TV and not detect other channels) and so it gradually became a less and less directly useful tool for the license enforcement teams to use, so it has sort of transformed from a genuine relatively accurate tool, into a sort of mythical boogeyman that gets used to scare people into paying for the license. The wikipedia article is actually pretty good for explaining how the older detection mechanisms worked https://en.wikipedia.org/wiki/TV_detector_van#Detection_tech...

In gr-dtv transmitter examples for Gnuradio, I see some times people use a resampler block before the RF hardware sink. Say our sampling rate is ~9.14Msps which satisfies the Nyquist criterion because our samples are complex numbers.

2.1. Thanks for that tip, I forgot that I was able to check the source code of the WBFM Receive block. As you have said, there are mostly the same. There are some differences between how values are picked. The WBFM Receive block would be a synonym of Quadrature demod => Fir Filter (decimation => Low pass filter) => FM Deemphasis. 2.3. My question there is why 10 and not 20 or 100. I understand that the idea is to reduce the sample rate asap, but what I don't understand is why those values were picked and how can I understand what would be the "correct" or "best" value. 2.4. I'm not fully understanding what you said. If I check the WB FM recieve source code the values that are supplied as the cutoff freq and transition width of the Low pass filter differ from the one of the example. The webfm would apply a sample rate / decimation / 2 - sample rate / decimation / 32 as a cutoff freq and a sample rate / decimation / 32 as a transition transition width. Calculating those values would end up in different that the ones supplied in this second example. Again, is there a rule of thumb to pick these values?.

Gaussian filter is used only on the tx side, so specifying bt in the receiver makes no sense. Take a look at gfsk mod/demod blocks implementation: https://github.com/gnuradio/gnuradio/blob/master/gr-digital/python/digital/gfsk.py

GNU Radio

Here's the filter coefficients used for the GNU-Radio interpolator block to get you started. This is a 7th order interpolator (i.e., 8 FIR taps) with very good performance. Each "row" of the array sets the delay in steps of sample_time / 128.

From their README: “open-source software development toolkit that provides signal processing blocks to implement software radios.” https://github.com/gnuradio/gnuradio