I do this at home, but I don't try to make absolute measurements.
You can easily use a dipole, just as the lab will do when they want an
accurate look at a specific spike. You'll need to do this outdoors, away
from emitters. For me that's a practical impossibility, as I'd have to cart
the equipment quite a ways to get to a quiet site.

What I did, is to build a shield enclosure from double-sided PCB material,
soldered together with brass reinforcements on the corners, and finger stock
to seal the lid. I use a small pickup loop to feed my spectrum analyzer, or
IC-R8500 receiver.

Use a small microwave tray to set your pcb up off the copper!

By itself, this will give you unreproducible and very frustrating results.
The next thing you need is some sheets of 3M Mosfoam. The stuff they ship
chips in.
Black, squishy, carbon loaded foam. This stuff absorbs RF quite nicely, and
you get double effect because what dosen't absorb is reflected by the copper
for another pass through the foam..
Line all the walls with this, and you'll be able to make repeatable relative
measurements.

Now, just find your highest spike, and kill it, repeat till it gets
difficult.

You can find some notes on this at www.dvanhorn.org