Signal processing algorithms can pull out a signal from well below the noise floor these days. Even the small and nondirectional antennas on your phone are good enough to receive GPS signals even all the way down at -125 dBm, which is WAY less than your phone receives in interference from random radio stations and faulty LED bulbs nearby.
The tech used to receive Voyager signals is not really different, just more sensitive and sophisticated (and expensive).
I think that would fall under the "must accept interference" portion of FCC Part 15, my phone communicating back to the tower might raise some alarms if I tried amplifying it at all though!
Because their power supply is shitty and it's easy to transform the chopper that is used in the switching power supply to behave as an oscillator instead, which will start to emit harmonics (https://en.wikipedia.org/wiki/Switched-mode_power_supply)
Electromagnetic radiation power roughly equivalent to the amount of light they output. I wished I was kidding, some of them are so bad they should qualify as jammers.
The tech used to receive Voyager signals is not really different, just more sensitive and sophisticated (and expensive).