I have an ICF-7600 and can test one with a good loop. I seldom use
it, but as I recall its AM section was really good. Not as good as
an SR3, but good. I think even a two foot loop would really boost
its AM up.
As far as copper tubing loops, some very careful, controlled
experimentation I have done in a Faraday cage with reference
antennas and an Agilent network analyzer has shown that the Q of the
loop has no relationship to the sensitivity. So copper tubing is a
needless expense unless you are going for a lot of Q. The crystal
radio people have very low resistance wire - 600 46 guage strand or
110 44 guage strand - that will beat copper tubing by a mile for
high Q tuned loops. So if your problem is separating stations, I
can get you some contacts. The wire isn't cheap, though. You are
dealing with garage crystal radio hobbyists who buy a reel, and then
charge through the nose for lengths of it.
