Over on his YouTube channel oh2ftg has uploaded two new RTL-SDR related videos. In the first video he does a tear down on the stock standard antennas that are supplied with most cheap RTL-SDR units. He finds that most are just a simple design, with the center conductor of the coax soldered to the whip, and the shield pinched between a metal plate and the base.
In his second video he measures the stock antennas on a Vector Network Analyzer (VNA). He places the antennas on a reasonably sized ground plane and finds that the antennas are as expected and pretuned to the DVB-T TV band at around 500 – 600 MHz.
Generally the included antennas are okay for receiving strong signals but we recommend getting yourself an outdoor discone antenna, or building a planar disk (pdf) for more serious scanning.