The KR87, which I thought was state of the art
doesn't do 0.5kHz either.
To befair to the much maligned ADF, it is as accurate as a VOR, subject to certain conditions
- over a large expanse of open water or flat terrain
- a good distance from the beacon
- no significant "weather"
and of course it is great as you cross the beacon as the needle flips around.
The rest of the time it can be pretty awful.
Nevertheless I decided, back in 2002, to get the KI-229 RMI factory fitted because the basic indicator is basically unusable for real approaches. Sadly the KI-229 indicator is an even bigger piece of *&*& than the ADF, packing up several times. Usually the 400Hz inverter goes.
Nowadays I fly all NDB and VOR approaches using the GPS OBS mode, and check the RMI at the TOD, etc.