When i put wlan0 in monitor mode it is hit and miss if i capture anything with airodump-ng

i have used the following commands

airmon-ng start wlan0

found 2 processes that could cause trouble.
PID Name
957 dhclient3
1462 dhclient3
process with pid 1462 (dhclient3) is running on inteface wlan0

interface chipset driver
wlan0 Ralink 2573 USB rt73usb - [phy0]
(monitor mode enabled on mon0)

airodump-ng mon0

sometimes i get no results, other times it works

is there anything i'm missing for setting this adaptor?