Here's what you do.
Connect both loops to the same radio at the same time.
Tune into a station, say 1000khz, and peak loop A on that station.
Now, leave that alone and now just adjust loop B slowly to 1000khz. You should find a spot where you can phase that station into oblivion just by tuning loop B. If you can get a null, but not very deep, then try turning one or the other loop just a little.
The aim is to get the station at the same signal strength on both antennas (by rotating loops), but slightly out of phase from each other (by tuning).
You can also do this with a loop and a wire. The wire needs an RLC circuit that's resonant in the BC band (use a 365mmf cap and a loop stick antenna). Then you are tuning the loop, the LC tuner circuit, and adjusting the R (5k ohm potentiometer) to get the signal strengths the same.
All a lot easier if you have an S meter to watch.
Takes some practice but it WORKS! =:^]
(can do the same thing on FM BC with directional beams. Same principle)