This is an old revision of the document!
“Buy a $10 radio and a $100 antenna” - Old ham radio saying.
The stock antenna supplied with the dongles is pretty hopeless. It is strongly recommended that a purpose built or purchased antenna is used and placed outside and as up high as possible.
Discone antennas are good omni directional broadband antennas. As the RTLSDR is very broadband (60MHz to 1700MHz) the broader the better.
The RTLSDR dongle is a digital TV receiver so the following antennas will work if you are stuck in the short term.