When looking for something else I came across the Becker ADF3502.
The general view has been that the only reliable ADF has been the King KR87, whose encapsulated antenna does not suffer from the moisture ingress problems which seem to kill the other products. But this Becker one can’t be that bad, since it is fitted as standard on the DA42 and they are heavily used in the FTO sphere, which as we know tends to fly a lot of NDB procedures.
However, the unit does seem to suffer from a lot of dip, which could be airframe/installation specific – here.
NDBs are gradually disappearing but that is a topic already heavily discussed 
The process is much slower than most had hoped for in years past.
The Becker unit is as if not slightly more reliable than the KR87 however Dip is an inherent problem with all ADF systems and cannot be eradicated.
Some of the problem is that at close ranges ( holding ) as the aircraft rolls the dip is compounded by quadrantial error, this error is largely a function of the conductive airframe and the mounting position of the loop antenna. This error can be minimised ( in the KR87 by adjustments in the antenna ).
I don’t see many people doing ADF loop swings but this can give very good results, I had a great deal of success with the PA28 that I once owned with the bearings being indicated forward and aft being very accurate and the same with the bearings at 090 & 270. The bearings between these points varied in accuracy but never by more than 5 degrees.
The problem with most ADF systems is that most owners don’t want to pay for two blokes to spend an hour or so driving the aircraft around in circles on the ground to get a system with and accuracy far better than most pilots can fly.
