vlt.it is a good website. It's on my list for projects.

I have gear that I have used to receive signals at 25Khz. Though not
license by the FCC, the signal supposed comes from a Navy base in
Washington state. However, no such signals come from Area 51.  Here is
the loop near the TTR, nulling the XSD beacon:
http://www.lazygranch.com/images/radio/bigassant.jpg
This is my recording of the LAX travelers information system radio that
I recorded parked on the gravel near the ET Highway
http://www.lazygranch.com/sound/lax_530_etgravel.wav
Clearly, the equipment is sensitive. Other than the PYD beacon coming
from near Groom Lake, I have found nothing of interest from Groom Lake
down to about 10Khz (the bottom end of my gear).

I seriously doubt you will catch anti-gravity aircraft with VLF
equipment, mostly because such technology doesn't exist except in Bob
Lazar's imagination. However, it is possilbe you will catch noise from
ground sensors, though I will say that I haven't detected any what is
known as "energized loops" in the ground. I think the vehicle detection
is done with passive sensors (magnetometers).