> can the government easily find out that the user they've noticed on the airwaves is located there and knock down your door?
Sadly, yes. A bunch of SDRs spread over the whole country with precise clocks or a scheme like the one used in ADS-B MLAT reception (that's based on using the internal SDR clocks without requiring precise clocks on the host) is enough to use multilateration to hone in on any kind of signal, even looking up in raw signals in the past.
If I were to guess, I'd assume that even in nominal democracies the secret agencies are already running such monitoring stations so it's probably already the case that, should need be, all communications can be triangulated.
The HF bands are all small enough to be sampled whole with a single cheap RTL-SDR each, a KiwiSDR can sample literally all of them at the same time, only the VHF/UHF bands need more dedicated equipment (e.g. a BladeRF) - all of that is inside the range that hobbyists can easily afford.
Sadly, yes. A bunch of SDRs spread over the whole country with precise clocks or a scheme like the one used in ADS-B MLAT reception (that's based on using the internal SDR clocks without requiring precise clocks on the host) is enough to use multilateration to hone in on any kind of signal, even looking up in raw signals in the past.
If I were to guess, I'd assume that even in nominal democracies the secret agencies are already running such monitoring stations so it's probably already the case that, should need be, all communications can be triangulated.
The HF bands are all small enough to be sampled whole with a single cheap RTL-SDR each, a KiwiSDR can sample literally all of them at the same time, only the VHF/UHF bands need more dedicated equipment (e.g. a BladeRF) - all of that is inside the range that hobbyists can easily afford.