4
AntSDR E200 - Gigabit Ethernet connected SDR supports 70 MHz - 6 GHz range (Crowdfunding)
(www.cnx-software.com)
Practically no.
I have used an RTL-SDR scanner to analyze traffic and draw spectrograms.
In the software defined radio world, I could not tell "whether it's night or I pulled my hat too far down". :P