I recently purchased RTL-SDR v3 dongle along with antenna kit. I used 60cm each length and built vertical dipole antenna with boom length of 58cm and listened to airband frequencies.The closest airport from where i listen to is almost 15kms away. The audio received is with a lot of noise. Hence i have decided to build an antenna for permanent installation almost 30ft above ground.
I think it would be better to ask the community that "what kind of (omnidirectional) antenna could I possibly build to hear more stations and with less noise on the given band?" There are a lot of constructions with different gains and directional patterns, and I'm sure you can imagine where the limiting factors are: time, money, available space and restrictions to erect masts, etc.
Concerning the noises, there can be more reasons of that: the signal level of the station you heard was too low, this can be improved by an antenna with higher gain placed higher above the ground, or there are electrical noises near to you, whose are harder to eliminate if possible, or there are powerful out-of-band signals near to you that may deteriorate your receiver's sensitivity. It is not sure that you only have to upgrade the antenna.
The AM (modulation) that is used traditionally on the airband fequencies is prone to pick up many kind of noises (compared to, let's say, the FM), but it is the best if more than one station is transmitting on the same frequency at the same time even occassionally - they will not render the others unintelligible.