[chemeris]

USB3 can pump up to 900mA @ 5V = 4.5W, which is pretty good. But each device has its own specs - e.g. LimeSDR has only 10dBm output power, because it doesn't have a built-in amplifier. So if you (1) don't attach a large antenna to it, (2) you operate in your basement, (3) you choose an unused ARFCn and (4) you operate in closed mode, you should be fine form technical perspective. That said, legality of this is up to you - check your local spectrum rules.

[dogma1138]

It also seems to have an option for an external power supply so you could potentially add more power to it.

I don't know what the specs for it are, but 1000mW is 20dBM which gives you a very nice coverage range on it's own and it's definitely possible to power that of USB alone.