The key it seems for me is to try to get away from the "residential" noise.
My Transoceanic seems to do a halfway decent job when lugged out into the soybean field.
Now I just have to rig up an antenna like WA8ZTZ has suggested
Easiest would be to strip the loopstick out of a junk AM radio, but If you are going to build your own, try getting a ferrite rod about 3-4" long and 3/8-1/2" diameter. Wind it with magnet wire... 26, 28, 30 awg whatever you got. #61 ferrite material works good, have also
had some luck with #43. None of these specs are super critical and you can always experiment if you wish.
Have also used spider web wound coils on plastic forms tuned with an air variable capacitor stripped out of an old AM
radio and inductively coupled it to the portable with good results. Lots to tinker with if you feel so inclined.
Don't forget the ground, that is half the circuit, your results won't be as good without it. If your field has good soil conductivity something as simple as a dog anchor screwed into the ground will work fine for a quick ultralight portable setup.
Wish there was a soybean field here for my portable setup... my QTH is in suburban RFI hell.